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    • Research Progress on Accumulation, Turnover and Stabilization of Microbial Residues in Soil

      ZHANG Bin, CHEN Qi, DING Xueli, HE Hongbo, ZHANG Xudong

      2022,59(6):1479-1491, DOI: 10.11766/trxb202012270705

      Abstract:

      Microorganisms are the engine driving the biogeochemical cycling of soil elements and play an important role in the transformation of soil organic matter (SOM). They decompose SOM and release CO2 into the atmosphere through mineralization on the one hand and transform SOM into their cell components through assimilation on the other hand. These cell components can be accumulated in the soil as microbial residues after their death. There is increasing recognition that microbial residues are important precursors of SOM formation and contribute significantly to long-term SOM stabilization. Therefore, this paper calls for scientists to pay more attention and study the role of microbial residues in the accumulation, turnover and stabilization of SOM, and possible underlying mechanisms. To achieve this objective, this paper first explains the processes of how microorganisms continuously produce microbial residues in soils via assimilation and emphasizes the extent to which microbial residues contribute to soil stable carbon (C) pool. Subsequently, this paper introduces the (i) quantification of microbial residues using amino sugar analysis, (ii) conversion of amino sugar data into microbial residue C data to account for the proportion of microbial-derived C in soil organic C and (iii) distinction of original- and newly-formed microbial residues with isotopic labelling techniques to indicate the turnover of microbial residues in soil. Furthermore, this paper summarizes the key external factors influencing the accumulation and turnover of microbial residues. These factors include: (1) nutrition management that can directly influence substrate availability for soil microorganisms and consequently the production and accumulation of microbial residues, even though soil fungi and bacteria may respond differently to substrate addition; (2) tillage practices which generally reduce the accumulation of microbial residues through the destruction of fungal hyphae and breakdown of soil aggregates; (3) land-use change that can permanently impact the contribution of microbial-derived C to soil organic C; and (4) climate change factors which include temperature elevation, elevated CO2 concentration and nitrogen deposition. The fourth section of this paper summarizes the potential stabilization mechanisms of microbial residues in soil, which include chemical protection by attaching to soil mineral surfaces, physical protection by occluding in soil aggregates and delayed decomposition due to the chemical structure of microbial residues. In the last section, some perspectives are provided for the scientific issues that need to be further studied regarding microbial residue contribution to SOM: (a) combine microbial residues with living microbial communities to link with the processes of microbial assimilation from both instantaneous and continuous perspectives; (b) explore the distribution process and stabilization mechanism of microbial residues with soil minerals; (c) investigate the accumulation and turnover of microbial residues in subsurface soils as soil physicochemical properties and microbial community composition change substantially with increase in depth. These discussions will provide a clue to clarify the role of microbial anabolism driving and involving SOM formation and stabilization as well as the underlying relationship between SOM turnover and microbial process in terrestrial ecosystem.

    • Research on Soil Microbial Invasion Based on Knowledge Graph Analysis and Its Development Trend

      CHEN Min, QIN Hua, CHANG Jianwei, XU Jianming, XING Jiajia

      2022,59(6):1492-1503, DOI: 10.11766/trxb202108260457

      Abstract:

      Objective The rapid development of the agricultural economy and animal disturbance can cause exogenous microorganism-wide transmission via food chains and environmental media. This can disturb the soil native community which might trigger microbial invasion and pollution.Method Based on the core collection database of the Web of Science, we conducted a bibliometric analysis to explore the research progress of microbial invasion by using the CiteSpace knowledge map analysis tool, VOSviewer visual analysis software and HistCite citation analysis tool.Result The results described as follows: (1) During the period between 2000 and 2021, the number of research articles addressing the topic of microbial invasion increased, and attracted increasing attention; (2) The United States, China, Germany, India, and Australia were the main contributors of academic articles in the field, and also established close collaboration with each other in recent years; (3) The co-occurrence analysis of keywords showed that microbiome and metagenomic were the top two research hotspots in this field in recent 20 years; (4) "Soil Biology & Biochemistry", "Frontiers in Microbiology", "PLoS One", "Plant and Soil" and "Applied Soil Ecology" were the top five journals in this field. Among the top 10 important papers on microbial invasion, keywords of papers were clustered into 3 parts: interaction between invasive microbes and indigenous microbial communities (Cluster 1); soil microbial invasion mechanism and influencing factors (Cluster 2); impact of soil microbial invasion on the plant (crop) phenotype and disease prevention and control mechanisms(Cluster 3); (5) The rapid development of high-throughput sequencing and metagenomics made the microbial invasion a research focus; (6) The future research in microbial invasion mainly focused on the interaction between microbial invader and specific resident species, and exploration of suppression mechanism to prevent and control pathogenic microbes.Conclusion This study demonstrates the various functional exogenous microbes with the potential to disturb the balance of native communities based on bibliometric analysis. The knowledge of soil native communities and exogenous invasive microbes have been widely explored due to the rapid development of high-throughput sequencing technology. Most researchers focused on the pathogenic microbes invading the soil ecosystem rather than beneficial microbes. This is because beneficial microbial invasion can effectively prevent soil-borne diseases, promote plant growth and remediate soil pollution, while pathogenic microbial invasion can cause a decline in crop yield, and even threaten animals' health through the food chain. Thus, this study draws attention to microbial invasion; both of artificially defined beneficial and pathogenic microbes, to enhance the understanding of soil microbial balance and health and to provide important support for soil health and green agricultural production.

    Research Articles
    • Dynamics and Prediction of Soil Salinization Parameters under the Amelioration of Heavy Coastal Saline-alkali Land

      XIE Xuefeng, PU Lijie, SHEN Hongyun, WU Tao, ZHU Ming, HUANG Sihua

      2022,59(6):1504-1516, DOI: 10.11766/trxb202101240043

      Abstract:

      Objective Soil salinization is one of the main types of land degradation, which seriously inhibits the improvement of soil quality and the growth and grain yield of crops. Reclamation of coastal land is increasingly being used as a means of raising agricultural productivity and improving food security in China. Determining the importance of potential influencing factors of soil salinization parameters and thus predicting their concentrations are important for formulating targeted control measures to improve soil quality and crop yield in tidal flat reclamation areas.Method In this study, six treatments including control (CK), organic manure (OM), polyacrylamide plus organic manure (PAM+OM), straw mulching plus organic manure (SM+OM), buried straw plus organic manure (BS+OM), and bio-organic manure plus organic manure (BM+OM) were applied to explore the effect of different reclamation treatments on different soil parameters. The effect of all treatments on soil salt content (SSC), pH, sodium adsorption ratio (SAR), and exchange sodium percentage (ESP) was analyzed and the main factors affecting the degree of soil salinization were identified. Thereafter, the multi-linear regression model (MLR), BP artificial neural network model (BP-ANN), and random forest model (RF) were conducted to predict the soil salinization parameters (SSC, pH, SAR, and ESP)using covariates, such as air temperature, precipitation, evaporation, wind speed, soil water content, soil temperature, and soil bulk density.Result The results indicated that the concentration of SSC, SAR, and ESP gradually increased, while the pH gradually decreased during the oat growing stage. All reclamation treatments effectively reduced the level of surface soil salinization. Among them, SM+OM treatment had the best inhibition effect on SSC, whereas BM+OM treatment had the best inhibition effect on soil pH, SAR and ESP. Besides, both meteorological parameters and soil properties had a significant impact on the level of surface soil salinization during the amelioration of coastal saline-alkali land. Additionally, the RF model performed much better than BP-ANN and MLR as it revealed a much higher coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE), and lower root mean square error (RMSE) than BP-ANN and MLR model.Conclusion The above results indicate that the reclamation treatments can effectively inhibit soil evaporation, improve soil structure, increase soil water holding capacity, and thus reduce the salinization level of surface soil. Our results also suggest that the RF model is a more powerful modeling approach in predicting soil salinization dynamics of coastal saline-alkali land due to its advantages in handling the nonlinear and hierarchical relationships between soil salinization parameters and covariates, and insensitivity to overfitting and the presence of noise in the data. Thus, our findings could provide a reference for predicting the soil salinization parameters in areas with similar environmental conditions.

    • A Study on Silty Soil Shear Strength and Its Influencing Factors in Different Vegetation Types in Benggang Erosion Area of Southern Jiangxi

      WEN Hui, NI Shimin, WANG Yitong, WANG Junguang, CAI Chongfa

      2022,59(6):1517-1526, DOI: 10.11766/trxb202012240707

      Abstract:

      Objective This study was designed to explore the distribution of soil shear strength under different vegetation restorations types in the erosion area of Benggang in southern Jiangxi, and to clarify the influence of soil basic properties on shear strength after restoration.Method The surface soil of various parts of the Benggang under three different vegetation types was used as our research object. We analyzed and studied the changes in soil basic properties and the change characteristics of shear strength parameters and their influencing factors using Path analysis and principal component analysis.Result The results showed that the shear strength from high to low was forest > arboreal forest > scrubland > grassland > erosion area, and the soil shear strength of arboreal forest was 29.74% higher than that of scrubland. As the terrain decreases, the capillary pores were increasing, and the proportion of fine particles such as clay particles and powder particles was also increased and converged under the lower slope. Moreover, the soil nutrient content was gradually increased as the recovery time increased. The cohesion of Benggang soil showed an increasing trend as the recovery period increased while the internal friction angle showed a slowly decreasing trend, and reached the maximum on the upper slope. Importantly, the cohesive force had a very significant correlation with organic matter and saturated hydraulic conductivity, and the internal friction angle also had a significant correlation with water content and bulk density. The total pores, capillary pores, clay content and soil saturated hydraulic conductivity were selected to characterize the shear strength of the soil undersaturation and a prediction equation (R2 = 0.80, RMSE = 5.95) was established, and it showed high reliability in prediction accuracy.Conclusion The research results reveal the control factors of shear strength under different vegetation types, which can provide a certain reference for soil restoration processes in the southern Benggang eroded area.

    • Effects of Maize and Soybean Roots on Topsoil Shear Strength of Red Clay on Sloping Farmland in Central Yunnan

      ZHANG Liyun, DUAN Qingsong, FAN Maopan, YANG Yali, CHENG Weiwei, LI Yongmei

      2022,59(6):1527-1539, DOI: 10.11766/trxb202012140689

      Abstract:

      Objective The area of sloping farmland in central Yunnan accounts for 61.14% of the total arable land area, and its sustainability is affected by serious soil erosion. Thus, it is urgent to study the positive effects of the rational allocation of vegetation on the sloping land space on improving soil erosion and maintaining sustainable agricultural production. About 89.4% of the sloping farmland utilization in the province is for planting crops, and maize and soybean are the main crops in summer. Previous studies have shown that the soil-fixing capacity of vegetation roots plays a significant role in soil and water conservation. This study was conducted to explore the soil-fixing effect of corn and soybean roots and to provide a basis for the calculation of the soil-fixing ability of crop roots.Method In this study, a field experiment was designed to have three treatments and a total of 9 experimental plots; i.e. CK (Bare land), MM (mono-maize) and SS (mono-soybean). The unconfined compression tests were used to determine the shear strength and stress-strain characteristics of rootless soil and root-soil composites of maize (Zea mays L.) and soybean (Glycine max L.) at the mature stage. The WinRHIZO (Pro.2019) system was employed to analyze the root distribution and configuration characteristics. And then the relationship between shear strength and root parameters was studied.Result The results indicated that: (1) Compared with rootless soil, the roots of maize and soybean significantly enhance the shear strength of root-soil composite (P < 0.01), and the strength of the root-soil composites was increased by 117.65% and 71.91%, respectively; (2) The cohesion of two crop root-soil composites were significantly positively correlated with root length density, root surface area density, root volume density, and root weight density (P < 0.01). Also, the contribution of fine roots with D ≤ 1 mm to the cohesive force increment was greater than that of other diameter-level roots; (3) In the different root architecture traits, the number of root branches of maize was 45.44% higher than that of soybeans, and the root distribution of each diameter class was more even. The corn root-soil complex showed weak strain-hardening characteristics when the root content was increased. Also, the crack propagation slowed down and the lateral deformation decreased.Conclusion The root systems of the two crops could enhance the shear strength of the soil. However, the different root structure types demonstrated different effects on the mechanical properties of the soil. The maize root system with more fine roots and more branches can effectively enhance the strength and restrain the deformation. Thus, fibrous root maize is better than taproot soybeans in holding the surface soil. In the use of sloping farmland, it is possible to prevent soil erosion by rationally arranging fibrous root crops. This study provides a reference for the rational layout of crop planting to prevent soil erosion on slope farmland.

    • Effect of Reduced Nitrogen Fertilization on Nitrogen Runoff Loss and Apparent Balance on Red-soil Dry Slope Peanut Land

      ZHENG Wenqi, TAN Wenfeng, LIU Zhao, WANG Lingyun, ZHENG Haijin

      2022,59(6):1540-1550, DOI: 10.11766/trxb202104070019

      Abstract:

      Objective Severe soil erosion and water leakage on dry slopes of red soils are a common phenomenon that results in significant nitrogen loss. These occurrences cause nitrogen imbalance and subsequent yield losses. This study aimed to explore the effects of different levels of reduced nitrogen fertilization on crop yield and nitrogen loss characteristics.Method Randomized field trials comprising of five nitrogen treatments in three replicates were set up in peanut fields located in the dry slopes of northern Jiangxi characterized by red soils. The five treatments were 100% nitrogen application rate (N100%, pure nitrogen application of 180 kg·hm–2), 1/6(N1/6), 1/3(N1/3), 1/2(N1/2), and zero (N0) nitrogen application rates.Result The peanut yield and plant nitrogen uptake of N1/2 and N1/6 treatments were insignificantly lower than those of the N100% treatment (P > 0.05). Besides, N1/6 and N1/2 treatments had no significant differences in agronomic characteristics such as the main stem length, plant height, crown width, number of full fruits, and the number of original branches (P > 0.05). N1/6, N1/3, N1/2, and N0 treatments significantly reduced the average total nitrogen (TN) concentration in the surface runoff by 14.36%, 26.35%, 14.01%, and 21.34%, respectively, compared to the N100% treatment (P < 0.05). Also, N1/3, N1/2, and N0 treatments reduced the average TN concentration in the leakage compared to the N100% treatment. However, the average increase in TN leakage concentration in the N1/6 treatment was not significantly different from that of the N100% treatment (P > 0.05). The nitrogen output from the peanut planting system ranged between 34.95 and 93.98 kg·hm–2. Nitrogen losses from runoff and leakage ranged between 38.31% and 70.50%, while other apparent nitrogen losses such as gaseous losses ranged between 29.50% and 60.63%.Conclusion This finding affirmed the significance of nitrogen loss through runoff and leakage. Non-nitrogen treatment on newly reclaimed land reduced the soil inorganic nitrogen while reduced-nitrogen fertilization increased the soil inorganic nitrogen by up to 18.66%-31.44%. Thus, reduced nitrogen fertilization could maintain a constant soil fertility level. Based on the comprehensive production goals, environmental impacts, and soil fertility, 90 kg·hm–2 is the recommended nitrogen application rate for peanuts planted in dry slope land with red soils.

    • Effects of Loose Soil Samples, Repacked Soil Columns and Compactness on Soil Organic Carbon Mineralization

      RONG Hui, FANG Huan, JIANG Yuji, ZHAO Xu, PENG Xinhua, SUN Bo, ZHOU Hu

      2022,59(6):1551-1560, DOI: 10.11766/trxb202104100187

      Abstract:

      Objective Soil organic carbon (SOC) mineralization is generally measured by laboratory incubation of loose soil samples. However, the structure of loose soil samples is of great difference from that of bulk soil samples. The relationship between SOC mineralization of loose soil samples and bulk soil samples is not clear. Soil samples close to field conditions can be obtained by repacking soil columns. Nevertheless, compactness can affect soil pore structure and may influence SOC mineralization. Therefore, this study aimed to evaluate whether it is accurate to represent SOC mineralization in the field by incubating loose soil samples and how compactness influences soil pore structure or SOC mineralization in repacked soil columns.Method Soil samples were collected from a long-term field experimental site with treatments receiving different amount of pig manure. In our first incubation experiment, all of these soils were selected and two treatments were set up in each soil: loose soil samples and repacked soil columns. In the second incubation experiment, only one soil was used, and the soil was repacked into columns with four bulk densities, which were 1.1(BD1.1), 1.3(BD1.3), 1.5(BD1.5) and 1.7(BD1.7) g·cm–3. The samples of these two experiments were incubated for 57 d and 28 d, respectively. SOC mineralization was measured during incubation, and soil pore structure was quantified using X-Ray micro-computed tomography (μ CT) imaging.Result At the end of incubation(57 d), the cumulative amount of SOC mineralization was significantly different between loose soil samples and repacked soil columns. The cumulative amount of SOC mineralization in the loose soil samples was about 4 times that of the repacked soil columns. In the second experiment, the total porosity decreased by 12.9%, 14.8% and 17.4%, respectively under BD1.3, BD1.5 and BD1.7 compared with BD1.1. In relative to BD1.1, the increase of compactness decreased macro-porosity by 19.0%, 65.5% and 88.5%, respectively under BD1.3, BD1.5 and BD1.7. In addition, the water-filled pore space (WFPS) increased from 36.4% to 91.8% and air-filled pore space (AFPS) decreased from 63.6% to 8.2%. At the end of incubation(28 d), the cumulative amount of SOC mineralization generally increased as bulk density increased up to 1.5 gžcm–3, after which there was a decrease. The regression analysis showed that there was a significant nonlinear relationship between the cumulative amount of SOC mineralization and total porosity, macro-porosity, WFPS and AFPS. The cumulative amount of SOC mineralization increased with increasing total porosity and macro-porosity until a level of 46% and 3.7% was respectively reached, afterwards it began to decline. Also, the relationship between the cumulative amount of SOC mineralization and WFPS and AFPS showed the same trend. The cumulative amount of SOC mineralization was the highest when WFPS was 66% or AFPS was 34%.Conclusion Laboratory incubation using loose soil samples will overestimate the potential of SOC mineralization in the field, while a change of compactness will modify soil pore structure and subsequently affect SOC mineralization. There is a significant nonlinear relationship between the cumulative amount of SOC mineralization and porosity.

    • Estimation of Soil Environmental Carrying Capacity and Its Application in the Determination of Remediation Target in Contaminated Sites

      DING Shoukang, WANG Meie, WANG Yujun, LI Xiaonuo, CHEN Weiping

      2022,59(6):1561-1573, DOI: 10.11766/trxb202102090088

      Abstract:

      Objective It is important to study the soil environmental carrying capacity for soil pollution prevention and control in "The Action Plan for Prevention and Treatment of Soil Pollution". Application of the estimation model of soil environmental carrying capacity could greatly improve the science content of the method of remediation target determination.Method Taking an abandoned chemical site in Jiangsu Province as a case study, the spatial distribution and health risk assessment of three target pollutants (i.e. mercury, hexachlorobenzene, and chlorobenzene) were analyzed based on soil sampling and investigation in the site. The environmental carrying capacities and remediation target values for the pollutants were estimated using the soil environmental carrying capacity model.Result The results revealed that more than half of the sites had soil mercury and hexachlorobenzene excessing their risk screening values, with about 17% for chlorobenzene. The spatial distributions of all three pollutants were mainly dependent on the distribution of the sources and manufacturing processes. Importantly, a serious non-carcinogenic risk is suggested for mercury and chlorobenzene, while a serious carcinogenic risk for hexachlorobenzene. Results of the soil environmental carrying capacity estimation suggested that, under a normal scenario and taking the risk screening value as soil quality standard, there were areas in the site having an environmental carrying capacity for all three pollutants less than zero. This indicated that the contamination of those areas excessed the soil environmental carrying capacities. Under an optimistic scenario and taking the risk controlling value as soil quality standard, the whole site had environmental carrying capacities for all three pollutants greater than zero. This suggested that the site can contain more pollutants.Conclusion The remediation target values calculated by the soil carrying capacity estimation model were 1.8 to 1.9 times higher than the corresponding risk screening and control values. This was due to the coefficient calibration during the processes of risk emergence, soil adsorption, and fixation of pollutants in the carrying capacity model. The results in this study can provide scientific and technical support for the development and application of soil environmental carrying capacity.

    • Research on Anaerobic Microbial Degradation of Polycyclic Aromatic Hydrocarbons Under Different Reducing Conditions: Analysis Based on Bibliometrics

      ZHU Yanjie, HE Yan, XU Jianming

      2022,59(6):1574-1582, DOI: 10.11766/trxb202102060081

      Abstract:

      Objective Polycyclic aromatic hydrocarbons (PAHs) are a kind of persistent organic pollutants that exist widely in various environmental media. As one of the most important ways to eliminate PAHs pollution in the environment, microbial degradation has been widely studied in the past few decades. Many of the polluted environmental media may undergo anaerobic states or remain in anaerobic states, e.g. paddy soils, bottom soils, wetlands, sediments, water. However, existing studies mainly focused on the aerobic environment and paid less attention to the anaerobic environment. Considering the current situation, this study systematically and comprehensively illustrates the research status of anaerobic microbial degradation of PAHs.Method The core collection database of Web of Science was used as the data source to conduct a bibliometric analysis of published literature in this field, with the aid of two pieces of software, VOSviewer and CiteSpace. The main contents of the bibliometric analysis included the year of publication, disciplines, keywords frequencies, keywords co-occurrence and most cited papers. In addition, by classifying different electron acceptors based on their reducing sequence, this paper discussed the research progress regarding anaerobic microbial degradation of PAHs in denitrification, metal ion reducing, sulfate reducing and methanogenesis conditions, respectively, with a focus on typical degrading microbes and mechanisms. On this basis, the existing theoretical gaps and future development trends in the field of PAHs anaerobic microbial degradation in the soil were discussed emphatically.Result The results showed that since 1991, the number of studies in this field showed the trend of fluctuating growth but was still relatively small on the whole, and most of them only focused on low-ring PAHs, especially naphthalene. Among the four different reducing systems, denitrification and sulfate reducing systems were studied more extensively, while less attention was paid to metal ion reducing and methanogenesis systems. Most significantly, the majority of mechanical studies remained at a relatively superficial level, without exposing the biological mechanisms of PAHs anaerobic microbial degradation and the interactions between functional microbes. Emerging technologies have not been commonly used in this field. Most studies were based on pure culture or environmental media such as water and sediment, but few were based on soil system.Conclusion As a result, there are still many theoretical gaps in the understanding of anaerobic microbial degradation of PAHs in the soil at present. Soil is the main site for the confluence and accumulation of PAHs in the environment. In the future, researchers should try to combine Compound-specific Stable Isotope Analysis (CSIA), DNA-stable isotope probing(DNA-SIP), Omics and other emerging technologies with traditional research methods to explore the mechanisms of PAHs anaerobic microbial degradation in the soil from a variety of different aspects, and verify the applicability of existing theories and experience to the soil, so as to fill the current theoretical gaps and promote the microbial remediation of PAHs pollution in anaerobic soil.

    • Interfacial Reactions between As (Ⅴ) and Cd (Ⅱ) Co-adsorption onto Various Mineral Surfaces

      HUANG Minxue, GUAN Yufeng, SU Zixian, TAO Liang

      2022,59(6):1583-1593, DOI: 10.11766/trxb202101140027

      Abstract:

      Objective pH is the most important environmental factor influencing the reactivity of heavy metals on mineral surfaces. The purpose of this study was to investigate the interfacial reactions between As(Ⅴ) and Cd(Ⅱ) adsorption/co-adsorption onto different mineral surface excluding the interference of pH.Method Three different minerals: Al2O3, TiO2, and kaolin, were chosen and passed through 100-mesh sieve. The experiments for As(Ⅴ) and Cd(Ⅱ) adsorption onto the different minerals were conducted in serum bottles (Effective volume = 2 mL) at pH 6.0. The bottles containing 0.02-1 mmol·L–1 As(Ⅴ), 0.02-1 mmol·L–1 Cd(Ⅱ), 28 mmol·L–1 4-Morpholineethanesulfonic acid sodium salt (MES), 100 mmol·L–1 NaCl and 2.0 mg of mineral powders were placed on a rotator at 200 r·min–1 and 25 oC. Batch studies were conducted to assess the adsorption kinetics, adsorption isotherm and the influence of molar ratio of As(Ⅴ) and Cd(Ⅱ) on the extent of As(Ⅴ) and Cd(Ⅱ) adsorption.Result The adsorption kinetics showed that As(Ⅴ) and Cd(Ⅱ) adsorbed onto different mineral interfaces followed the pseudo-second-order kinetics model, and chemical adsorption was the rate-controlling steps. Furthermore, the normalized adsorption capacities of Cd(Ⅱ) and As(Ⅴ) were ranked as TiO2 > Al2O3 > kaolin. The adsorption abilities of As(Ⅴ) and Cd(Ⅱ) were enhanced by the co-existing Cd(Ⅱ) and As(Ⅴ). Specifically, the addition of As(Ⅴ) promoted the adsorption of Cd(Ⅱ) onto Al2O3, while the addition of Cd(Ⅱ) enhanced As(Ⅴ) adsorption onto TiO2. The synergistic effect of As(Ⅴ) and Cd(Ⅱ) co-adsorption was mainly controlled by the electrostatic adsorption and the ternary complex formation. Moreover, with the increase of Cd(Ⅱ)/As(Ⅴ) concentration ratio, the regulation mechanism of Cd(Ⅱ) adsorption gradually changed from the electrostatic adsorption to the synergy of the formation of interfacial - As(Ⅴ)- Cd(Ⅱ) ternary complex and electrostatic adsorption, and then changed to the formation of surface precipitate. Importantly, with the increase of As(Ⅴ)/Cd(Ⅱ) concentration ratio, the key regulation mechanism changed from adsorption controlling to surface precipitation controlling.Conclusion Electrostatic adsorption, formation of interfacial - As(Ⅴ)- Cd(Ⅱ) ternary complex, and surface precipitation were the critical mechanisms controlling the interfacial reactions between As(Ⅴ) and Cd(Ⅱ) adsorption onto various mineral surfaces at various ratios.

    • A Coupled Amidation - Liquid Chromatography Technique for Detecting Low Molecular Monocarboxylic Acid in Pedosphere Samples with High Sensitivity

      CHEN Hong, TANG Haoye, ZHONG Ming, LIU Xiaodong, WANG Ruhai, YU Yuanchun

      2022,59(6):1594-1605, DOI: 10.11766/trxb202103080130

      Abstract:

      Objective Formic, acetic, propionic and butyric acid exist widely in the natural ecological environment, but their contents are usually low. Thus, their accurate qualitative and quantitative determination is often hindered by impurities in the sample matrix.Method Using the coupling amidation method, low molecular monocarboxylic acids (LMMAs) can form new derivatives with high sensitivity to ultraviolet (UV) light. This was achieved by incorporating the indole group into LMMAs' structure, which made it possible for the low-level LMMAs to be detected by high-performance liquid chromatography with diode array detector (HPLC-DAD) under a specific wavelength UV light with high response. As a result, we observed the accurate determination of LMMAs. Through experimentations, we propose the following steps: first, a suitable amount of sample and MES (2-Morpholinoethanesulfonic Acid) aqueous solution were added into a small bottle with the reaction system adjusted to about pH≈5.5. This was followed by the addition of EDC (1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) aqueous solution. After 20 minutes of cross-linking reaction, a suitable amount of NHS (N-Hydroxy succinimide) aqueous solution was added to promote coupling reactions. After an appropriate period, a tryptamine aqueous solution (containing acetonitrile) was added into the reaction system for amidation overnight. This was followed by the addition of ultrapure water to a certain volume and prepared for determination.Result The experimental results showed that for an optimized observation, the mole ratio of MES: EDC: NHS: tryptamine: carboxylic acid should be maintained at about 10 : 7 : 3 : 7 : 1 around and after 45 minutes of coupled reaction and the addition of tryptamine aqueous solution for amidation. The detection limit for the four organic acids in this method was from 0.008 to 0.046 mg·L–1, and the linear determinate coefficient R2 of the standard working curve was around 0.991~0.998. The average recovery rate range was 85.9%~123%, and the precision of the method ranged between 1.69%~8.41%, which meets the requirements of organic analysis.Conclusion The actual sample test results showed that the data of the derivation method and the direct method were the same. However, compared with the HPLC direct detection method, the derivation-HPLC method could correct the positive error caused by the impurities in complex samples, and improve the detection rates of low concentration monocarboxylic acid samples. So the qualitative and quantitative results of the derivation-HPLC method were more reliable.

    • Mechanisms in Plant Growth Promotion by Novel Bio-organic Fertilizer Containing Sorbitol

      FANG Dan, ZHU Mingzhu, WEI Mengyu, YANG Yuting, XUE Chao, SHEN Qirong

      2022,59(6):1606-1615, DOI: 10.11766/trxb202012040672

      Abstract:

      Objective In this study, a novel bio-organic fertilizer was designed by adding sorbitol, which is one of the preferred carbon sources for the functional strain Bacillus amyloliquefaciens SQR9, to the normal bio-organic fertilizer rich in strain SQR9(2×108 CFU·g–1). The plant growth promotion effect was evaluated. The mechanism for elevation of plant growth promotion effect of the normal bio-organic fertilizer by sorbitol addition was studied.Method The effect of this novel bio-organic fertilizer on cucumber growth, soil biological and chemical properties was evaluated by pot experiments. The effect of sorbitol on plant growth promotion and stimulating IAA (indole-3-acetic acid) production by strain SQR9-gfp was investigated by culturing experiment using Arabidopsis.Result The pot experiment showed that the application of this novel bio-organic fertilizer could promote cucumber growth by increasing the soil nutrient availability and the colonization of strain SQR9-gfp. The addition of sorbitol could promote IAA production by strain SQR9-gfp. Comparing to the wild type Arabidopsis, the plant growth promotion effect of sorbitol addition vanished on the IAA insensitive mutant Arabidopsis pin2.Conclusion These results suggest that the application of this novel bio-organic fertilizer can promote plant growth. The addition of sorbitol can promote IAA production by SQR9-gfp and this is one of the mechanisms through which the novel bio-organic fertilizer boosted plant growth.

    • Several Problems about Dynamic Chamber Technique in Determining Ammonia Volatilization from Rice Fields

      TIAN Yuhua, YIN Bin, ZENG Ke, ZHAO Xu

      2022,59(6):1616-1625, DOI: 10.11766/trxb202012310721

      Abstract:

      Objective Ammonia emitted from agricultural fields has led to significant adverse effects on air, soil and water environment. To evaluate the fate of applied nitrogen fertilizers, guide the rational application of nitrogen (N) fertilizers and eliminate the adverse environmental effects caused by ammonia volatilization (AV), it is important to measure AV in field conditions. The dynamic chamber method is commonly used in determining AV from rice fields. However, there are still some drawbacks associated with this method. These limitations lead to the incomparability between different research results and thus affect the systematic analysis and assessment of regional ammonia emissions from farmland.Method In this study, the effects of the air exchange rate, time of the measurement, characteristics of the dynamic chamber, types of air-washing device, and the difference between vacuum pumping and natural wind environment on AV were studied.Result Results showed that AV increased with the increase of air exchange rate. Overall, there were three stages during the increase of AV which was linearly correlated with the logarithm of the air exchange rate. The diurnal variation of AV was different between the period of rapid hydrolysis of the applied urea and the period after rapid hydrolysis of urea. As for the types of air-washing device, AV values measured with the spherical porous and straight through types were 25.6% and 8.5% lower than that measured with disk porous type, respectively. The larger the inner diameter and the lower the height of the gas phase of the dynamic chamber are, the lower the ammonia volatilization is. Volatilized ammonia absorbed by two gas washing bottles in series is only 88.6% of that absorbed by the single gas washing bottle. The evaporation within the dynamic chamber increased with the air exchange rate. Although the amount of surface water loss within the container which was ventilated via vacuum pumping was similar to that under the natural ventilation environment, AV of the former container is relatively low. This indicates that the process of AV is affected to some extent by the vacuum pump and air-washing system.Conclusion It is obvious that the influencing factors such as air exchange rate, measurement period during the rapid hydrolysis of applied urea, characteristics of the dynamic chamber, and the air-washing device should all be considered in measuring AV. The transparent dynamic chamber (diameter 15 cm) connected with a separate flowmeter and only one gas-washing bottle, containing gas-washing holes on the side of the disk or the end side of the straight rod, airflow rate of 15-20 L·min–1, and the gas phase height of 5-8 cm are recommended to be employed in measuring ammonia volatilization from rice fields.

    • Long-term Fate and Availability of Residual Fertilizer Nitrogen in Rice-Wheat Cropping System in Taihu Lake Region of China

      WANG Yingying, XIA Longlong, CAI Siyuan, ZHAO Xu, YAN Xiaoyuan, XING Guangxi

      2022,59(6):1626-1639, DOI: 10.11766/trxb202203180119

      Abstract:

      Objective The high chemical nitrogen (N) fertilizer input in cropland soils of China has caused a large accumulation of residual fertilizer N in the soil in the current-season. This soil-residual fertilizer N can either be absorbed by subsequent season crops or lost to the environment through gaseous and hydrological pathways. The rice-wheat rotation is a dominant vital cropping system in the middle and lower reaches of the Yangtze River agricultural region in China. However, the residual effects and fate of the soil-residual fertilizer N in this cropping system remain unclear.Method In this study, a 15N tracer long-term in-situ experiment was used to continuously monitor the fate and the residual effect of soil-residual fertilizer N in the following 17 years under non-fertilizer N application in a rice-wheat cropping system. The experiment had two N fertilizer treatments, with 100 (N100) and 250 (N250) kg·hm–2 of labelled urea (30 atom%) applied in the first wheat season, and no N fertilizer was added in the subsequent 17 years of the rice-wheat rotation.Result The results suggested that 34.5%-37.9% of the applied fertilizer N was taken up by the first wheat crop, and then the amount of residual N uptake by the rice and wheat decreased exponentially in the following rice-wheat rotation years. Over the following 17 years, 12.2%-15.8% of the applied fertilizer N was taken up by the subsequent crops (9.2%-11.8% for rice and 3.3%-4.0% for wheat), leading to the accumulative crop N recovery of 50.1%-50.3%, which was significantly higher than the in-season N use efficiency. We found that 22.9%-33.5% of the applied fertilizer N remained in the 0-20 cm soil after in-season wheat was harvested, which was then gradually decreased to 7.8%-9.8% after 17 years, but still accounted for 73.5%-78.5% of the total residual N in the 0-100 cm soil layer (9.9%-13.4%). The cumulative total loss of fertilizer N over the observation period estimated from the isotope mass balance was 36.3%-39.9%, which was close to the total loss of fertilizer N of 32.0%-39.2% calculated based on the N fertilizer use efficiency and the residual rate of 0-20 cm soil in the current season. The 15N abundance of crop grain, straw and soil all decayed exponentially with time during the observation period, which predicted that it would still take 28-37 years for the crop to decrease to the natural 15N abundance background value without N application.Conclusion Overall, fertilizer N losses in the rice-wheat cropping system mainly occurred in the current-season, and the residual effects of fertilizer N in soil lasted for a long time, but a negligible amount of this residual N can be lost to the environment. The keyways to optimal N fertilizer management in rice-wheat rotation are effectively reducing in-season fertilizer N losses and better utilizing soil-residual fertilizer N.

    • Soil Phosphorus Pool Evolution and Environmental Risk Prediction of Paddy Soil in the Taihu Lake Region

      WANG Yu, YUAN Jiahui, CHEN Hao, CHEN Guanglei, ZHAO Hongmeng, XU Lingying, ZHAO Xu, WANG Shenqiang

      2022,59(6):1640-1649, DOI: 10.11766/trxb202012160696

      Abstract:

      Objective Agricultural sustainable development and aquatic ecological environment security are faced with numerous challenges. As a non-renewable resource, phosphorus (P) is an essential element for crop growth, but has the potential to cause water eutrophication. Disparities in P management such as fertilizer or manure and the harvested crop P removal result in a massive variation of P imbalances in agricultural systems. Phosphorus loss is mainly affected by the form and availability of soil P.Method Therefore, in this paper, considering strong spatial differentiation characteristics of soil P pools and availability, the soils of typical flood and drought rotation farmlands were selected. The farmlands were located in the Taihu Lake Region in the lower reaches of the Yangtze River. In detail, 319 farmland soil samples and 83 wheat samples were collected based on the systematic random point distribution method. The spatial differences of soil phosphorus fractionations and crop P uptake were analyzed.Result Compared with the results of the second national soil survey and the survey in 2009, soil total P (TP) and available P(Olsen-P)increased significantly in the Taihu Lake Region. Soil Olsen-P concentration in Changshu and Yixing city ranged between 2.19-112.5 mg·kg–1 and 5.21-109.7 mg·kg–1, respectively. The average concentration was 37.6 mg·kg–1 and 29.8 mg·kg–1, which increased by 24.6 mg·kg–1 and 7.9 mg·kg–1 --in contrast to 2009. The concentration of available P exceeded 10 mg·kg–1 of 93.1% of soil samples, and 65.2% of the total soil samples had more than 20 mg·kg–1, which indicated that most of the paddy soil P pool was in surplus. Furthermore, we analyzed soil P availability using the biologically-based P (BBP) method, and found that CaCl2-P, Citrate-P, Enzyme -P and HCl-P had a significant positive correlation with Olsen-P (P < 0.001). This indicates that those four P forms were all available sources of soil P. We also found a notable relationship between soil TP and Olsen-P (P < 0.001) or crop TP (P < 0.01) concentration. Meanwhile, the correlation analysis of CaCl2-P and Olsen-P indicated the breakpoint of environmental risk, which was 30 mg·kg–1.Conclusion In view of the strong spatial differences of soil phosphorus pools in this region, it is suggested to focus on the efficient utilization of soil phosphorus in the regional nutrient management and environmental protection. The results are expected to provide basic data support for increasing P use efficiency as well as agricultural non-point source pollution control in the Taihu Lake Region.

    • The Soil Microbial Legacy Effects of Long-term Gradient P Fertilization Based on the Analysis of Plant Growth, Nutrient Absorption, Soil Enzyme Activity and Mycorrhizal Characteristics

      LANG Ming, ZHANG Chunyan, ZHANG Junling

      2022,59(6):1650-1659, DOI: 10.11766/trxb202104300231

      Abstract:

      Objective Long-term excessive phosphorus (P) application in intensive agro-ecosystem leads to P accumulation in soil. Whether there was a legacy effect on accumulated P in soil.Method This study was based on a long-term experiment (started in 2007) in North China Plain. The microorganisms with different P supply levels (from P2O5 0, 75, 300 kg·hm–2, P0, P75, P300, respectively) in calcareous soil was selected as the research object. Pot microbial inoculation experiment was conducted to explore the soil microorganisms training with gradient P fertilization on plant growth, nutrition absorption, soil enzyme activities and mycorrhizal characteristics under two substrate P supply levels (0 mg·kg–1, 30 mg·kg–1, no P, + P, respectively).Result The type of inoculants (original inoculants, sterilization treatment) significantly affected the aboveground biomass and phosphorus uptake of plants. Inoculating original inoculants (P0, P75 and P300) significantly increased the aboveground biomass and P uptake of clover compared with sterilized inoculants under the condition of two substrate P levels, but there was no significant difference among the three original inoculants. The aboveground biomass of maize inoculated with original inoculants P300 was significantly higher than that in the treatments of P0 and P75. At the same time, the inoculant and substrate P supply level co-affected soil enzyme activities. Compared with P0 and P75 inoculants, P300 inoculant significantly decreased the peroxidase activities in the soil of clover under no P and + P conditions, and significantly increased the peroxidase and chitinase activities in the soil of maize under no P conditions. Also, compared with inoculating in original P0 and P300 inoculants, P75 inoculant significantly increased the activities of acid and alkaline phosphatase in maize soil under no P condition. In addition, the mycorrhizal colonization differed due to plant species. Compared with P0 and P75 inoculants, the colonization rate of arbuscular mycorrhizal fungi in clover root significantly reduced after inoculating with P300, but there was no significant difference among the three original inoculants in maize root.Conclusion The substrate P supply and plant species co-affect microorganisms training by accumulated P, suggesting that plant-microbial characteristics need to be considered in P fertilizer management.

    • Characteristics of Enhanced Microbial Thermogenic Functions in Hyperthermophilic Composting

      CUI Peng, AI Chaofan, LIAO Hanpeng, ZHOU Shungui

      2022,59(6):1660-1669, DOI: 10.11766/trxb202102050077

      Abstract:

      Objective Hyperthermophilic composting (hTC) exhibits significant advantages during organic solid waste treatment such as nitrous oxide mitigation, nitrogen retention, antibiotic resistance genes removal compared with those of conventional composting (cTC). Such advantages are closely linked with hyperthermophilic temperatures However, the reason for extremely high composting temperature remains unclear.Method Here, by using PICRUSt (physiological investigation of communities by reconstruction of unobserved states), the variations in microbial function during hTC and cTC using chicken manure were studied. The reason for the extremely high composting temperature in hTC was explored.Result Results show that the composting temperature could reach up to 80℃ and last for more than 5 days in hTC. hTC exhibited significant differences in both the composition of the microbial community and their metabolic pathways abundance during the hyperthermophilic stage. The abundances of thermogenesis related metabolic pathways (such as energy metabolism, carbohydrate metabolism) and aerobic respiration chain-related genes (such as NADH dehydrogenase gene, succinate dehydrogenase gene) were significantly increased during the hyperthermophilic stage (P < 0.05). Furthermore, the abundance of the enriched metabolic pathways and functional genes was significantly correlated with the temperature variation of hTC (P < 0.05). Random forest regression models comparing the predicted to actual composting temperatures found strong correlations in both treatments (for hTC, adjusted R2 =0.96; for cTC, adjusted R2 =0.97). The model indicated that the abundances of K03943(NADH dehydrogenase flavoprotein 2), k15862 (cytochrome c oxidase cbb3-type subunit I/II) and k05580 (NADH-quinone oxidoreductase subunit I) were the most important factors affecting the composting temperature in hTC. By comparison, the highest composting temperature of cTC was below 70℃, and the abundance of metabolic pathways and functional genes related to heat production was significantly negatively correlated with compost temperature (P < 0.05).Conclusion Our results suggest that the hTC community might metabolize organic matter more rapidly by significantly increasing the abundance of functional genes related to the aerobic respiration chain, thus increasing the rate of ATP synthesis and generating more metabolic heat.

    • The Relationship between Soil Microbial Population Asynchrony and Crop Yield in Rice-Wheat Rotation with Gradient Nitrogen Inputs

      LI Minghui, FENG Xumeng, GUO Junjie, GUO Shiwei, SHEN Qirong, LING Ning

      2022,59(6):1670-1682, DOI: 10.11766/trxb202106250131

      Abstract:

      Objective The object of this study was to explore the effect of nitrogen addition rate on the relationship between soil microbial diversity and asynchrony in rice-wheat rotation.Method We collected soil samples at key growth stages in rice-wheat rotation under different nitrogen addition rates in a long-term experiment and used high-throughput sequencing technology to analyze the effect of nitrogen addition rate on soil microbial diversity. Also, we explored the effects of nitrogen addition rates on yield by altering soil microbial asynchrony. The gradient N addition rates in field experiment were 0, 50, 100, 200, 300 kg·hm–2 for wheat and 0, 90, 180, 270, 360 kg·hm–2 for rice. The key growth stages when soil samples were collected include: fallow before wheat planting, jointing, booting, flowering, and maturing during the wheat season, and fallow before rice planting, max-tillering, shooting, flowering, and maturing during rice season.Result N addition rates impacted soil microbial diversity and composition in each growth stage, and the N addition rate could significantly account for about 12% variations of microbial richness in the rice period. When the N addition rates were 100 or 180 kg·hm–2, soil microbial diversity in the wheat or rice seasons, respectively, was maintained at a relatively high level across all plant developmental stages. Also, the N addition rate could significantly account for 9%-11% variations in microbial community composition in the wheat and rice period. With the increase of N addition rate, the asynchrony of some microbial populations was significantly increased during the wheat (e.g. Phenylobacterium, Sphingomonas, Cyanobacteria GpI, Desulfovirga, Lacibacter, Terrimonas) and rice seasons (e.g. Desulfovirga, Spartobacteria genera incertae sedis, Ohtaekwangia, Acidobacteria Gp7, Arenimonas, Niastella). Importantly, the wheat and rice yields showed positive relationships with the asynchronies of Phenylobacterium and Desulfovirga and with the asynchronies of Desulfovirga, Spartobacteria genera incertae sedis, Ohtaekwangia and Arenimonas, respectively.Conclusion Nitrogen addition rate has a constant impact on soil microbial diversity in rice-wheat rotation during plant development, which changes microbial population asynchrony, and then improves certain functional complementation to increase crop yield. The results of this study can provide a scientific basis and practical guidance for regulating soil microbial communities to maintain high crop yield.

    • The Effect of Iron Oxides on Mineralization, Transformation and Priming Effect of Acetate in Anoxic Paddy Soils

      WANG Yunqiu, LI Yuhong, ZHU Zhenke, WU Jinshui, GE Tida

      2022,59(6):1683-1694, DOI: 10.11766/trxb202105270277

      Abstract:

      Objective Acetate is an important substrate for methane production, and its mineralization and transformation are key to the carbon cycle, carbon sequestration, and greenhouse gas mitigation in paddy soils. In long-term flooded paddy soils, iron, an important valence-variable metal, may influence the mineralization and transformation of acetate.Method Therefore, 13C-acetate, ferrihydrite and goethite were added into paddy soil and the CO2 and CH4 emissions were monitored. Also, the changes in paddy soil properties during anaerobic incubation (100 days) were analyzed. Additionally, we analyzed the characteristics of mineralization and transformation of acetate and its priming effect on CO2 and CH4 to reveal the roles of different types of iron oxides.Result The results showed that in the acetate treatment after incubation, 33% and 36% of acetate was mineralized to CH4 and CO2, respectively, while 0.12%, 2% and 28% were transformed to dissolved organic carbon (DOC), microbial biomass carbon (MBC) and soil organic carbon (SOC), respectively. Acetate caused a negative CO2 priming effect and a positive CH4 priming effect. The ratio of CO2 to CH4 sourced from soil organic carbon was changed from 3.46: 1 to 1.83: 1 by acetate addition. Goethite addition significantly increased acetate derived cumulative CO2 emission, while ferrihydrite showed no significant effect. Ferrihydrite and goethite significantly decreased SOC derived CO2 emission and strengthened the negative CO2 priming effect of acetate. Also, ferrihydrite and goethite significantly decreased acetate derived CH4 emission and showed no significant effect on SOC derived CH4 emission. The proportions of acetate transformed to MBC and SOC were significantly increased in the presence of ferrihydrite and goethite.Conclusion The mineralization and transformation of acetate influenced CO2 and CH4 emission from native SOC. Ferrihydrite and goethite, different in crystallinity, have different effects on mineralization, transformation and priming effect of acetate. Thus, this study can provide theoretical and technical support for carbon sequestration and greenhouse gas mitigation in paddy soils.

    • Response of Paddy Soil Anammox Bacteria to Rice Straw Returning and Different Tillage Practices

      SUN Mei, NIE San'an, LONG Zedong, LI Chao, WANG Hua, XIAO Xiaoping, LUO Zunchang, SUN Geng

      2022,59(6):1695-1703, DOI: 10.11766/trxb202109010267

      Abstract:

      Objective This study was carried out to evaluate the response of paddy soil anammox bacterial activity, abundance and community structure to rice straw returning and different tillage practices.Method Three different till treatments (conventional till, rotary till and no-till) + rice straw returning were set up, with conventional till and no rice straw returning as control. The potential activity, functional gene (hzsB) abundance and community structure of anammox bacteria were analyzed by 15N tracing, fluorescent quantitative PCR and Illumina sequencing, respectively.Result Anammox activity showed a significant difference and the values ranked as no-till > rotary till > conventional till(P < 0.05), while no significant difference was observed between control and rotary tillage+rice straw. Also, no significant difference was detected in the copy number of hzsB among treatments. Two known anammox bacteria (Kuenenia and Scalindua) and some unidentified genera were identified by Illumina sequencing, and the relative abundance of Kuenenia and Scalindua showed a negative correlation (P < 0.05). Pearson correlation analysis showed that anammox activity was significantly correlated with denitrification activity, but not with hzsB abundance and community composition.Conclusion We conclude that anammox activity and community composition but not the functional gene abundance respond to long term straw returning and different tillage practices. Rice straw returning + conventional till in rice field may inhibit N loss to some extent, while rice straw returning + no-tillage increased soil N loss. This study may provide a scientific basis for nitrogen (N) management in paddy fields.

    • Soil Microbial Diversity is Higher in Pure Stands of Moso Bamboo than in Pure Stands of Chinese Fir

      YAN Shuxian, LIU Ming, LIU Caixia, ZHAO Mengli, QIU Wei, GU Jiayue, FENG Gelin, GAO Jing, CAI Lingxiao, XU Qiufang

      2022,59(6):1704-1717, DOI: 10.11766/trxb202107190169

      Abstract:

      Objective It is a common phenomenon for most of the artificial Chinese Fir Forests (CF) to have continuous cropping obstacles, while the Moso bamboo forest (MB) rarely does. As an important indicator of soil health, soil fertility has a non-negligible effect on microorganisms.Method Our study used high-throughput sequencing to analyze the soil bacterial and fungal communities in three different forest stands.Result The results showed that both the Shannon index and Invsimpson index of soil bacteria and fungi in MB were significantly higher than those of CF and even higher than that of Broadleaf forest (BL); while the Berger-Parker index in CF was significantly higher than that in MB. The relative abundances of Actinobacteria and Basidiomycotawas in MB were higher than that in BL and CF, while the relative abundances of Chloroflexi and Mortierellomycota in CF were significantly higher than that of MB and BL.Conclusion Combined with the analysis of soil physicochemical properties, it was shown observed that the nutrient content of the studied soils played a very significant role in influencing the microbial community structure, Moreover, MB had a conductive environment for the formation of a good microbial community structure compared to the other soils. It was concluded that the soil bacterial and fungal characteristics and soil physicochemical properties of MB stands were more similar to those of broadleaf than to those of CF.

    • Microbial Community Structure and Environmental Response of Desert Soil in Hexi Corridor

      LI Shanjia, WANG Fuxiang, Cong Wenqian, Wei Ming, Wang Junqiang, CUI Lijuan, Wang Zihao

      2022,59(6):1718-1728, DOI: 10.11766/trxb202110120235

      Abstract:

      Objective The survival and adaptation mechanisms of microorganisms in desert soils and their ecosystem functions are of great significance for revealing the process of material transformation in arid areas.Method In this study, 16 transects were set up along the gradient of natural precipitation from the southeast to northwest of the Hexi Corridor. High-throughput sequencing technology was used to explore the characteristics of soil bacterial and fungal community diversity, revealing microbial diversity, dominant flora and soil mechanical composition, and nutrients relationship.Result The results showed that Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the dominant communities in the desert soil bacteria of the Hexi Corridor. The abundance of Firmicutes is up to 85%. Ascomycota and Basidiomycota are the dominant fungi communities, and their relative abundances are both greater than > 5%. Correlation analysis showed that: coarse powder particles (0.05-0.02 mm), fine powder particles (0.25-0.10 mm), clay particles (< 0.002 mm), available phosphorus(AP)and alkalization nitrogen (AN) have a great influence on bacterial diversity Significantly, fine powder (0.25-0.10 mm), clay (< 0.002 mm), available phosphorus (AP) and alkalization nitrogen (AN) have a significant impact on fungal diversity (P < 0.01). Redundant analysis showed that fine powder (0.25-0.10 mm), available phosphorus (AP) and soil organic carbon (SOC) had significant effects on bacterial communities, while clay particles (< 0.002mm) and available phosphorus (AP) had significant effects on fungal communities (P < 0.05).Conclusion The results of this study explored the composition, changes and influencing factors of the desert soil microbial community structure in the Hexi Corridor, explained the influence of the soil environment on the distribution of microbes and the role of microbes on the development of the soil ecosystem, and served to protect biodiversity and desert ecosystem Provide theoretical reference.

    Communications and Comments
    • Analyses and Corrections of Formula Errors in Soil Soluble Salt and Its Components Calculation

      YUAN Jinhua, QIAO Wandekua, E Shengzhe, CHE Zongxian

      2022,59(6):1729-1746, DOI: 10.11766/trxb202102180101

      Abstract:

      Objective There are many errors in soil soluble salt and its component formula in published professional books. However, this has not attracted enough attention and no corrections have been made. Such published data may induce wrong results in soil soluble salt and its components calculation and subsequently wrong judgments in the classification or grading of saline-alkali soils.Method 12 professional books published during 2000~2020 and containing 9 indexes (soil soluble salt, CO32–, HCO3, SO42–, Cl, K+, Na+, Ca2+, Mg2+) were selected for use in deriving their formulas based on related concepts, theoretical basis, experimental principles and experimental methods.Result Results suggested that there were 68 total errors using the 9 indexes. Among the 9 indexes, HCO3 recorded the highest frequency of errors, i.e. 11 times and accounted for 16.2%. It is followed by Ca2+ which recorded 10 times in total and accounted for 14.7% while soil soluble salt and Cl recorded the lowest, i.e. 4 times in total (5.88%). Based on analyses of the characteristics of errors with the 9 indexes, the errors were found to occur as five different aspects categorized as coefficient 2, conversion coefficient, formula, reference and formula unstandard. Out of the five categories, conversion coefficient recorded the highest frequency of errors, i.e. 31 times in total (45.6%); followed by formula at 13 times (19.1%) and the coefficient 2 with the lowest of 4 times (5.88%).Conclusion Errors in soil soluble salt and its component formula were discovered in published data and corrective measures were applied accordingly. The characteristics and causes of errors in calculating the formula of soil soluble salt and its components were suggested. Also, our results suggest reference values for the corrections of relevant formula.

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      • Effects of Potassium Addition on Physiological Characteristics and Grain Yield Under Drought Stress Condition in Different Growth Stages of Rice

        XIONG Zhihao, YANG Cheng, ZHANG Geng, LI Xuchun, LI Xiaokun

        DOI: 10.11766/trxb202205230267

        Abstract:

        【Objective】As one of the most important food crops in China, rice (Oryza sativa L.) is the staple food for more than half of the country""s population. With the development trend of global warming and frequent occurrence of extreme weather such as sustained high temperature, drought on farmland is becoming a more frequent and urgent problem. Thus, this study seeks to clarify the effects of drought stress on rice at different growth stages, the regulation of potassium on drought stress and its mechanism, and to provide a theoretical basis for the management of potassium and efficient water use in rice.【Method】A two-factor pot experiment of K and water treatments at different periods was carried out in 2021. Potassium management was two levels of 0.15 (+K) and 0 (?K) g?kg?1 soil(calculated as K2O), moisture management was four levels of drought stress at the tillering stage (TD), drought stress at booting stage (BD), drought stress at milking stage (MD) and well-watered treatment (WW), to explore the effects of K fertilizer on rice yield and physiological characters under drought stress at different growth stages. 【Result】Results showed that drought stress significantly decreased rice yield. Compared with the WW treatment, TD, BD and MD treatments decreased rice yields by 53.9%, 45.2%, and 7.6% under K deficient conditions, respectively, while under K sufficient conditions, rice yields reduced by 28.3%, 16.5% and 5.9%, respectively. The degree of influence of drought stress on yield in different growth stages was: TD > BD > MD, and K deficiency aggravated the negative impact of water deficit on rice yields. Similarly, drought stress also caused a decrease in canopy transpiration rate, leaf water potential, leaf net photosynthetic rate, and limited dry matter accumulation. Compared to the WW treatment corresponding to the same period, TD and BD treatments reduced leaf biomass by an average of 42.9% and 31.2%, respectively. The stem sheath biomass decreased by 43.8% and 38.0%, respectively, and the effect of water deficiency on biomass in different growth stages was: TD > BD. Potassium deficiency resulted in a reduction in net photosynthetic rate, leaf area and chlorophyll content, which restricted the ability of plants to receive light radiation and produce dry matter. Compared with the K-sufficient treatment, the leaf biomass of the TD and BD and WW treatments at the same stages decreased by 52.6%, 32.7%, 42.1%, and 31.2%, respectively. Also, under potassium deficient conditions, stem sheath biomass decreased by 55.3%, 63.6%, 52.2%, and 28.0%, respectively. Drought stress exacerbated the negative effects of potassium deficiency. 【Conclusion】Our results indicated that drought stress could limit the net photosynthetic rate and leaf water potential, resulting in the reduction of rice yield, which affects the tillering stage and booting stage more than the milking stage. Potash application significantly increased leaf area, increased chlorophyll content, enhanced the ability of rice to intercept light radiation, improved rice photosynthetic efficiency, and increased rice dry matter accumulation, while reducing canopy transpiration rate, improving water use efficiency, alleviating the decline of leaf water potential, thereby enhancing the drought resistance of crops.

      • Influencing Mechanisms of Humic Acid and pH on the Migration Behavior of Typical Tire Wear Particles

        LI Kun, KONG Deyue, CHEN Xingyue, PENG Yonghong, XIU Xiaojia, SU Han, PAN Minyu

        DOI: 10.11766/trxb202206200329

        Abstract:

        【Objective】Tire wear particles (TWPs), as one of the important types of microplastics (MPs), have received a lot of attention from ecologists for their ecological risk in recent times. Usually, the environmental behavioral processes of particulate pollutants are important influencing factors of their ecological risk. However, the migration process and influencing mechanisms of TWPs in porous media such as soil have not been reported so far. 【Method】In this paper, C-TWPs prepared by freezing crushing and R-TWPs (rolling friction) and S-TWPs (sliding friction) produced by road wear were selected as typical research objects, and quartz sand columns were used to simulate and study the migration behavior of TWPs in environmental porous media such as soil, and to investigate the effects of natural organic matter humic acid (HA) and different pH (4, 7 and 10) environments on the migration behavior of the above three types of TWPs.【Result】The results showed that HA (50 mg?L-1) significantly enhanced the mobility of the three types of TWPs, and the migration behavior of TWPs was differently affected by different pH (4, 7 and 10) environmental conditions in the presence of HA (50 mg?L-1), with the medium-alkaline environment (pH = 7/10) being more favorable for the migration of TWPs. This was mainly due to an increase in the negative zeta potentials of the surfaces of TWPs and quartz sand particles in the presence of HA and/or the medium alkaline environment (simultaneously). Also, the dispersion of TWPs was improved for smaller particle size distribution while the electrostatic repulsion between TWPs and quartz sand particles was increased, which contributed to the migration of TWPs. It is worth noting that the migration of C-TWPs prepared by low-temperature crushing was stronger than that of R-TWPs and S-TWPs in the presence of HA and under different environmental pH conditions. This was mainly attributed to the fact that C-TWPs carried a larger negative charge, smaller isoelectric point and stronger hydrophobicity, and these properties also contributed to the adsorption of more HA, thus enhancing their electronegativity. Nevertheless, R-TWPs and S-TWPs had less electronegativity on the surface due to the adhesion of road minerals, metal salts or dust that reduced the magnitude of the mentioned properties.【Conclusion】These results reveal the variability of the geochemical transport behavior of different types of TWPs in nature and suggest the necessity of studying the source properties (discharge mode) to determine the inherent differences in environmental behaviors and ecological risks of microplastics of the same material.

      • Effect of Exogenous Rice Straw on Water Dispersible Colloidal Metals in Polluted Soil Under Redox Change

        ZHANG Yu, WANG Jiajia, XIA Bing, LUO Xueting, HU Pengjie†, WU Longhua, LUO Yongming

        DOI: 10.11766/trxb202204110168

        Abstract:

        【Objective】Soil colloids, especially water-dispersible colloids (WDC), as pollutant carriers, play important roles in heavy metal adsorption, migration, and biological absorption. The purpose of this study was to explore the effect of exogenous rice straw and redox change on the distribution of heavy metals in the aqueous phase of the soil and water-dispersible colloids. 【Method】In this study, soil microcosm experiments were conducted for 70 days, in which 0-40 days was the reduction period, and 41-70 days was the oxidation period. The experiment comprised two treatments: (i) no straw added (CK), (ii) rice straw added (1% of the soil weight, S). The different chemical parameters in the aqueous phase of the soil were comprehensively compared, and the particle size classification and elemental composition of WDC during the redox process were characterized by asymmetrical flow field-flow fractionation (AF4) coupled to UV and ICP-MS (AF4-UV-ICP-MS) method. 【Result】The results showed that in anaerobic conditions, exogenous rice straw increased aqueous concentrations of dissolved organic carbon (DOC), arsenic (As), iron (Fe), manganese (Mn), calcium (Ca), potassium (K), silicon (Si), aluminum (Al), and magnesium (Mg), while it decreased aqueous redox potential (Eh) and the concentrations of copper (Cu) and lead (Pb). In aerobic conditions, exogenous rice straw increased aqueous concentrations of Pb. Results from AF4-UV-ICP-MS indicated that the size of WDC was mainly distributed at three size ranges, 0.3-3 kDa, 3-40 kDa, and 130 kDa-450 nm with different complexes of organic matters, inorganic clay minerals, and ferriferous minerals. A significant proportion of heavy metals in the aqueous phase were bound to WDC particles, which indicated that WDC played an important role in the environmental behavior of these pollutants. WDC with different particle sizes tended to combine different kinds of heavy metals. Exogenous rice straw affected the distribution of heavy metals in WDC particles and this effect was related to the nature of the elements. Also, exogenous rice straw promoted the transformation of Fe and As from WDC state to the dissolved state, while promoting the transformation of cadmium (Cd) and Cu from dissolved state to the WDC state. 【Conclusion】Water-dispersible colloids were important carriers for heavy metals in the aqueous phase of the soil. Exogenous rice straw and redox change affected the behavior of WDC associated heavy metals related to the nature of elements. This study is important as it reveals the interface mechanism of how agricultural activities affect the migration, transformation, and bioavailability of heavy metals.

      • Effects of long-term different tillage practices on chitin degrading microbial communities and chitinase activity in farmland black soil

        Sui Pengxiang, Luo Yang, Li Ruiping, Zheng Hongbing, Yuan Ye, Zheng Jinyu, Wang Hao, Liu Wuren

        DOI: 10.11766/trxb202203180120

        Abstract:

        【Objective】This study aimed to illustrate the impacts of different tillage practices on chitin degrading microbial communities and chitinase activity in farmland black soil, and to explore the main environmental factors in driving a change in chitin degrading microbial communities and chitinase activity. 【Method】Based on the long-term positioning platform of different tillage practices in black soil and the combination of fluorescence quantification and high throughput sequencing technology, this research intends to study the effects of long-term different tillage practices (Conventional tillage, No-tillage, Sub-soiling tillage, Moldboard plowing tillage) on chitin degrading bacteria harboring chiA gene abundance, microbial communities and chitinase activity in 0~40 cm soil layers. 【Result】Results showed that no-tillage increased chiA gene abundance in the 0~20 cm soil layer. Lower chiA gene abundance, alpha diversity and proteobacteria relative abundance, and higher actinobacteria relative abundance in the 20~40 cm soil layer of no-tillage than other tillage practices. The abundance of chiA gene and microbial community structure was significantly affected by soil pH, mean weight diameter and nutrients. Compared with conventional tillage, the chitinase activity increased in 0~20 cm soil layer under no-tillage, and the chitinase activity was enhanced in 0~40 cm soil layer under sub-soiling tillage and moldboard plowing tillage. The simulation result of the structural equation modeling showed that chitinase activity was directly affected by the tillage practice, soil depth, mean weight diameter, organic carbon, total nitrogen, total phosphorus, chiA gene abundance, and actinobacteria relative abundance. 【Conclusion】These results provide a theoretical basis for understanding the effect of different tillage practices on soil chitin degradation in black soil areas.

      • Remediation of Lead-contaminated Soil by Superparamagnetic Micro-nano MFH Functional Materials

        li jie, wang qiang, luo meng, jiang xiang ting, sun yuan peng, zhang li zhi

        DOI: 10.11766/trxb202204290220

        Abstract:

        【Objective】This study aimed to effectively, rapidly , and cost-effectively purify wastewater and repair soil from lead pollution. 【Method】The remediation effect of a lead-remediation material (superparamagnetic micro nano Fe3O4@Ca10(PO4)6(OH)2 functional material, MFH) on Pb2+ in wastewater and polluted soil was studied in terms of dosage, initial concentration of Pb2+, adsorption time, pH, ionic strength and organic matter concentration. 【Result】The results showed that the adsorption of Pb2+ in solution by MFH satisfies the pseudo-second-order kinetic model. The adsorption equilibrium was reached in about 10 min, and the maximum adsorption capacity was 181.6 mg·g-1; at pH 2.00~5.00. Also, the removal rate of Pb2+ in the pH range decreased with the increase of pH while an increase in ionic strength of the solution inhibited the removal rate of Pb2+ by MFH. Nevertheless, an increase in the organic matter content in the reaction system effectively improved the removal rate of Pb2+ by MFH. MFH showed a good lead-removal effect when applied to lead-contaminated soils in farmland and industrial parks. The addition of heavy metal activator EDTA can significantly improve the removal effect of MFH on lead in soil. In slightly lead-contaminated farmland soil, the total amount of lead removed was 102.74 μg·g-1. After experimentation, the recovery rate of MFH from soil was over 88% by using a magnetic rod, while the recovery rate of MFH regeneration performance was 89.49%. Importantly, the magnetic properties and specific surface area of the regenerated MFH recovered well, suggesting that MFH had a good recovery and regeneration ability. 【Conclusion】Therefore, MFH is a good material for the decontamination of lead-contaminated wastewater and soils and its usage is promising given that it can easily be recovered with its basic properties intact.

      • Effect of Manure with Biomass Carbon on Forms of Nutrients and Nitrogen in Rhizosphere / Non-Rhizosphere Soils

        LI Yue, WANG Ying, XIONG Zi-yi, XIE Jun, WANG Zi-fang, GAO Ming

        DOI: 10.11766/trxb202206200331

        Abstract:

        【Objective】To clarify the effects of fertilizer and organic fertilizer combined with biochar on the forms of nutrients and nitrogen in rhizosphere / non rhizosphere soil, which is helpful for the efficient utilization and scientific management of farmland nitrogen .【Methods】Taking the pot experiment of lemon as the research object, this paper set up six treatments: no fertilizer (CK), chemical fertilizer (CF), manure (M), chemical fertilizer with biochar (CFB), manure with biochar (MB) and fresh manure with biochar (FMB). By measuring the changes of nutrient content in rhizosphere and non rhizosphere soil and the transformation of soil nitrogen storage forms, the effects of organic fertilizer combined with biochar on the forms of soil nutrients and nitrogen in rhizosphere and non rhizosphere were studied. 【Result】The results showed that compared with CK treatment, MB treatment increased non rhizosphere and Rhizosphere Soil pH by 0.32 and 0.28 units, and FMB treatment increased rhizosphere soil pH by 0.63 units; MB and FMB treatments increased the content of organic matter in rhizosphere soil by 25.37% and 84.88% respectively, and significantly increase the total nitrogen content of Rhizosphere Soil by 25.42% and 50.93%. Combined application of biochar (CFB, MB and FMB) could promote the transformation of soil non convertible nitrogen (NTF-N) to two more active nitrogen forms, iron manganese oxide bound nitrogen (IMOF-N) and organic sulfide bound nitrogen (OSF-N). IMOF-N and OSF-N accounted for 35.85%~61.72% and 26.65%~46.56% of convertible nitrogen, respectively, and were the main components of rhizosphere and non rhizosphere soil convertible nitrogen (TF-N). Therefore, manure combined with biochar is the most effective way to improve nutrients and regulate nitrogen transformation in rhizosphere and non rhizosphere soil.

      • Effects of the Deposition of Atmospheric Particulate Matter on the properties of Urban Soils: Evidence from Magnetic Susceptibility of Road Dusts

        WANG Xindong, HU Xuefeng†, ZHANG Yanshuo, CUI Lei, LIU Rui, LAN Wenchong, LI Mei, WANG Jiayuan

        DOI: 10.11766/trxb202206060235

        Abstract:

        To study the effects of deposition of atmospheric particulate matter (APM) on the properties of urban soils, the values of magnetic susceptibility (χlf) and heavy metals in the topsoils and road dust in the industrial, traffic, residential and agricultural areas of Baoshan District, Shanghai, were analyzed. The topsoils in the different functional areas of Baoshan District, Shanghai, commonly have significantly enhanced magnetic strength (χlf = 130.7×10-8 m3?kg-1 on average) of about 86.2% higher than the local magnetic background. χlf of the road dusts nearby the topsoils in the different functional areas was even more significantly enhanced, which was 903.3×10-8 m3?kg-1 on average. Likewise, heavy metal contents in the road dust were significantly higher than those in the nearby topsoils in the different functional areas. The contents of Cu, Zn, Pb, Cd, Ni, Cr, Co, Mn and Fe in the road dust were 3.4, 2.4, 4.7, 22, 1.5, 2.8, 1.2, 1.4 and 1.6 times of those in the topsoils on average, respectively. Moreover, χlf of the topsoils in the Baoshan District was extremely significantly correlated with the contents of Cu, Zn, Cd, Ni, Cr and Mn (P < 0.01), and also significantly correlated with Pb and Fe (P < 0.05). Likewise, χlf of the road dust was also significantly correlated with the content of Zn, Ni, Cr, Co, Mn and Fe (P < 0.01), and with Cu (P < 0.05). Nevertheless, such correlations in the different functional areas of the district are highly different. Those in the agricultural topsoils are not significant. The distinctive characteristics of the road dust in the studied areas suggested that the APM under the urban environment contain a certain amount of anthropogenic magnetic particles enriched in heavy metals. The long-term and continuous deposition of such magnetic pollutants has led to the enhancement of magnetic signals and heavy metal contents in urban topsoils synchronously, and also adversely impacted the properties of urban soils significantly.

      • Functions of Plant Growth-Promoting Bacteria and Their Application in Sustainable Agriculture

        MA Ying, CAO Mengyuan, SHI Xiaojun, LI Zhenlun, LUO Yongming

        DOI: 10.11766/trxb202203160112

        Abstract:

        Global climate change and population growth exacerbate various biotic (e.g., infection of pathogens) and abiotic (e.g., drought, salinity, high temperature, etc.) stress in agricultural production, which impede plant growth, development and productivity by affecting plant morphology, physiological and biochemical characteristics as well as metabolic functions. Consequently, this affects crop yield and quality and seriously threatens agricultural sustainability. With the vigorous development of modern agriculture, beneficial microorganisms have attracted much attention due to their ability to improve soil quality and fertility, stress tolerance in crops, and their yield and quality. Besides, the proper use of microbial inoculum in agricultural production can achieve the effects of reducing the amounts of agrochemicals, reducing production costs, improving the quality of agricultural products, and protecting the ecological environment, which is also in line with the agricultural production goal of harmonious coexistence between humans and nature. In this review, the types and application effects of plant growth-promoting bacteria (PGPB) were briefly summarized, with emphasis on the analysis of PGPB""s ability to produce phytohormone, fix nitrogen, facilitate the absorption and utilization of nutrients (phosphate and potassium solubilization and siderophore production), alleviate biotic and abiotic stress, regulate plant root architecture and rhizosphere microbial community structure. Moreover, the frontier science and technology of PGPB inoculum preparation and application methods in modern agriculture in recent years were systematically explored, and the application prospect and research direction of PGPB in future agricultural production were further discussed.

      • Rapid Diagnosis and Assessment of Heavy Metal Pollution in Greenhouse Vegetable Production Soils Based on Portable X-ray Fluorescence Spectroscopy

        DENG Yuan, FAN Yanan, WU Qiumei, HU Wenyou, YU Yueming, WANG Hua, ZHU Chunwu, LI Xun, TIAN Kang, HUANG Biao

        DOI: 10.11766/trxb202206130187

        Abstract:

        【Objective】Guangdong is a major province of vegetable production and consumption in China, and is also an important vegetable production base for Hong Kong, Macao, and the "Southern Vegetables and Northern Transportation". Therefore, rapid diagnosis and assessment of soil heavy metal pollution is the premise of soil pollution prevention and control and risk management. This study aimed to investigate the applicability of in situ and ex situ portable X-ray fluorescence spectroscopy (PXRF) for rapid detection of heavy metals in greenhouse vegetable production soils of Guangdong Province and to diagnose and evaluate heavy metal pollution in greenhouse vegetable production soils based on portable X-ray fluorescence spectroscopy. 【Method】A total of 110 greenhouse vegetable production soil sampling sites and 26 open-field soil sampling sites were set up in the study area. PXRF was used in situ to rapidly detect soil heavy metal contents (Cd, Cu, Cr, Pb, Zn, As, Ni and Hg). The accuracy of the PXRF method was verified by analyzing the correlation between the values of soil heavy metals measured by the PXRF and the traditional laboratory analysis and based on this, the soil heavy metal pollution status was quickly diagnosed. The risk of soil heavy metal pollution was evaluated by the single factor pollution index and the Nemerow composite pollution index method. 【Result】The results indicated that: (1) the concentrations of Cd, Cu, Cr, Pb, Zn, As and Ni detected by the ex situ PXRF method were significantly correlated with those determined by traditional laboratory methods (P < 0.01), and the R2 were 0.69, 0.50, 0.56, 0.58, 0.47, 0.54 and 0.62, respectively. Also, the results of in situ determination of Pb and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R2 were 0.73 and 0.74, respectively. (2) When the soil moisture content was 150 g?kg-1-200 g?kg-1, the results of in situ determination of Cr, Pb, Zn and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R2 were 0.77, 0.94, 0.72 and 0.93, respectively. (3) Soil Cd and Cu pollutions were prominent in greenhouse vegetable production soils of Guangdong Province. The point exceeding rates were 20.9% and 10.0%, respectively, according to the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). In addition, the average content of Cd in greenhouse vegetable production soil was 0.21 mg?kg-1, which was 1.2 times greater than that in open-field soil. The contents of Cd, Cu, Cr, Pb, Zn, As and Ni in the greenhouse vegetable production soil in the Pearl River Delta were generally higher than those in other areas. (4) The single pollution index of Cd, Cu, Cr, Pb, Zn, As, Ni and Hg were all less than 1, and the order was Cd > Cu > Pb > Zn > Cr > As > Ni > Hg. The mean value of the Nemerow comprehensive pollution index was 0.69. From the overall average, the degree of soil heavy metal pollution was at a clean level.【Conclusion】In summary, PXRF is an effective method for the rapid diagnosis of heavy metal pollution in greenhouse vegetable production soils in Guangdong Province. Furthermore, Cd and Cu can be quickly identified as the primary pollution elements with high risk in greenhouse vegetable production soils of Guangdong Province. The results of this study will serve as a reference for the evaluation of soil environmental quality and sustainable development of greenhouse agriculture.

      • Progress and Prospect of Research on Constructed Technosols

        ZHENG Ruilun, ZHU Yongguan, SUN Guoxin

        DOI: 10.11766/trxb20226200209

        Abstract:

        Urban green infrastructure is an effective way to solve many environmental issues caused by urbanization. As urban soils are generally not suitable for vegetation growth, a lot of soil resources needed for urban green infrastructure construction can only be excavated and transported from the exurban farmland and/or natural topsoil to urban areas, or in another way, urban soils are planted vegetation after fertilized with organic waste. These methods tend to be costly, destructive to arable land, induce large carbon emissions, and/or have a high cumulative risk of pollution. The huge amount of soil resources needed for the construction of urban green infrastructure is very scarce and this has to be addressed urgently. Constructed Technosols (CT) is a new soil created by using organic and inorganic solid wastes (including artefacts and also seminatural sediment and excavated deep soil-like things) for growing plants, which can be adjusted to meet the requirements of various vegetation types, land uses, site conditions (roof, balcony, street, etc.) in physicochemical properties and pollutant limit standards, and finally returned to the city for green infrastructure construction. CT can simultaneously alleviate the pressure of disposal of urban solid waste and solve the issue of soil shortage in urban green infrastructure construction. It features low carbon, low cost and low eco-impact, and can also produce economic benefits. In this paper, firstly, it was briefly stated the definition, classification and construction techniques of CT. And, the research status and advances mainly in terms of roles in plant growth, carbon capture, biodiversity protection, runoff pollutant removal, and artificial biological intervention of CT were presented. Then, it was briefly described the production of solid waste in China, and according to the current research and application situation, it was proposed the application potential (such as ornamental plant breeding and cultivation, sod production and urban farming etc. in addition to the park, green buffers, green roof and brownfield remediation like things) and advantages of CT. Finally, based on comprehensive research progress, some problems in CT research were pointed out and some insights and suggestions were put forward. Meaningful research on the ecological risk of pollutants in CT, biochar (hydrochar or pyrochar) application to CT, soil heterogeneity design for plant diversity, biological regulation of CT good for human health, promotion of environmental function for CT, and role of carbon sequestration by CT were proposed and supposed. It was aimed that comprehensive reutilization of urban solid waste and more eco-friendly low-carbon development of urban green infrastructure will be able to be promoted, urban carbon sequestration will increase, and urban ecological environment and people""s health and well-being will be improved.

      • The Progress and Prospect of Soil Compaction by Agricultural Machinery in Arable Land: A Review

        REN Lidong, WANG Li, LIN Lin, ZHANG Bin

        DOI: 10.11766/trxb202110270582

        Abstract:

        Soil compaction by agricultural machinery has become one of the most serious soil degradation problems in the world. This paper reviewed the research progress of soil compaction from four aspects: detection, impact, alleviation and prevention of soil compaction. It shows that new detecting methods are urgently needed for field soil compaction detection. The impact of soil compaction is mostly focused on the top cultivated soil layer, but the effects of subsoil compaction and its potential ecological services in addressing climate change have been overlooked. Reasonable agricultural management strategies such as crop and tillage rotation methods could be applied to alleviate soil compaction. Overall, subsoil compaction is difficult to alleviate in a short period and prevention should be the top priority although there is still a lack of practical prevention methods. Agricultural mechanization in China is still in the early development stage, and effective preventive measures should be taken to avoid soil compaction like that in developed countries.

      • Effect of the Acidification Environment on Exchangeable Cations and Acid Buffering Capacity of Weathering Products of Purple Parent Rock

        LI Chunpei, LI Xue, WANG Xuan, LIU Gangcai, ZHAO Jixia, XIONG Junfen

        DOI: 10.11766/trxb202203200121

        Abstract:

        【Objectives】This study aimed to analyze the influence of the acidification environment on weathering products of the typical purple parent rock. The weathering products of purple parent rocks from the Suining Group (J3s), Shaximiao Group (J2s), and Penglaizhen Group (J3p) were investigated under different acidification environments in the laboratory. 【Method】 The acid solutions used for acidification of purple parent rock samples were used to cycle soaking and simulate leaching experiment tests at pHs of 2.5, 3.5, 4.5, and 5.6. In addition, deionized water (pH = 7.0) was set as a control treatment (CK). 【Result】 The results showed that the exchangeable cations and content of total exchangeable cations of weathering products of these purple parent rocks decreased as the acidity of the acidifying solutions increased. The acid buffering capacity of weathering products had an extremely significant correlation with the content of the exchangeable K+, Na+, Ca2+, and Mg2+ and the content total of exchangeable cations (P < 0.01). Compared with the value at pH = 7.0 (CK), the total content of exchangeable cations of the weathering products of purple parent rock of the groups J3s, J3p, and J2s in cycle soaking experiment tests decreased by 8.75%-18.21%,10.83%-23.18%, and 5.85%-18.41%, respectively. When the amount of simulated rainfall at 24 times was compared with that at 12 times, the total content of exchangeable cations in J3s, J3p, and J2s decreased by 1.77%-24.85%, 8.99%-25.75%, and 8.05%-25.66%, respectively. In addition, the exchangeable cations characteristics of the weathering products were Ca2+> Mg2+> Na+ > K+ under the same acidity treatment. 【Conclusion】The acid buffer capacity, exchangeable salt ions, and total salt of weathering products under the soaking treatment in this experiment were lower than under the leaching treatment. It can be seen that the transport of minerals or nutrients on the slopes of hilly areas is dominated by leaching, while the transport of minerals or nutrients on the plains is dominated by leaching. Therefore, acid deposition may accelerate the occurrence of soil erosion on slopes to some extent, which in turn leads to an acceleration of the plain side process.

      • Research and Practice on Sustainable and Safe Utilization of Soil in Agricultural Land -- A Case Study of Cadmium Contaminated Farmland in Zhejiang Province

        WANG Jie, ZHU Youwei†, YANG Xiaoe, GUO Bin, WANG Yulei

        DOI: 10.11766/trxb202205120170

        Abstract:

        【Objective】The sustainable and safe utilization of agricultural soil is of great significance to effectively improve the quality of the agricultural soil environment, and to ensure the quality and safety of agricultural products and human health.【Method】Taking Zhejiang Province, one of the most developed areas in the Yangtze River Delta, as an example, the main problems and development trends of agricultural land soil environment were analyzed, and the theory and method of sustainable and safe utilization of agricultural land soil were studied. During the 13th Five-year Plan period, based on the survey results of agricultural land soil pollution in Zhejiang Province at a scale of 1:50 000 over the years, provincial pilot demonstrations focusing on the control of heavy metal cadmium pollution in agricultural land were carried out in Wenling City and Tonglu County. The methods of pollution source analysis and prevention, multi-dimensional agricultural safety utilization technology screening and application, and safe disposal of over-standard crop straws were comprehensively adopted to form a batch of agricultural land soil pollution comprehensive treatment technology models with significant regional characteristics, high-efficiency control effects, and independent intellectual property rights, which are suitable for mild to moderate and moderate to severe cadmium pollution.【Result】The main results were as follows: (1) Atmospheric deposition source is one of the main external input sources of Cd in the agricultural land ecosystem, accounting for about 24%-59% of the total input. (2) 58 varieties with low accumulation (mainly Yongyou 538) were screened out, 20 passivation materials with calcareous substances as the main, and 10 leaf resistance control materials with silicon and selenium as the main were selected. (3) The safe utilization technology mode of rice/wheat rotation, which is suitable for light and moderate Cd polluted agricultural land can effectively reduce the available state of Cd in soil by more than 20%-50%. The production and remediation technology mode which is suitable for moderate and severe Cd polluted agricultural land, mainly with hyperaccumulators, can effectively reduce the total amount of Cd in soil by more than 30% and the available state of Cd in soil by more than 50%.【Conclusion】This paper innovatively puts forward the general idea and technical route of sustainable and safe utilization of heavy metal polluted agricultural land soil. It also summarizes the experience and strategy of sustainable and safe utilization of heavy metal polluted agricultural land soil, to provide a demonstration model and technical reference for the safe utilization of contaminated agricultural land soil in China.

      • Retention Capacity and Release Potential of Soil Phosphorus in Paddy Red Soil Pedogenic Horizons with Different Planting Years

        NIU Ben, WANG Yanling

        DOI: 10.11766/trxb202205160257

        Abstract:

        【Objective】This study aimed to analyze the change of phosphorus fixation capacity and release potential in different occurrence layers of red paddy soil, to clarify the release mechanism of fixed phosphorus(P), and to evaluate the loss risk of P in red paddy soil with different planting years.【Method】Soil samples were collected from the bottom to the top of three typical red paddy fields in Yingtan, Jiangxi Province. These paddies included a mid-phase paddy field (MP), a new paddy field (NP) and an old paddy field (OP). Based on the adsorption-desorption experiment and structural equation model, the variation differences and influencing factors of phosphorus retention capacity (PSI), maximum capacity of soil fixed phosphorus (MCSP) and the release potential of the soil were analyzed.【Result】With the increase of pedogenic horizons depth, PSI and MCSP of red paddy soil gradually increased, and the order of their changes were: MP > NP > OP and NP > MP > OP. The desorption capacity of electrostatically adsorbed state P (CaCl2-P) of OP, MP and NP profiles and the desorption capacity of specific adsorbed state P (EDTA-P) in the OP profile gradually decreased with the increasing profile depth. Also, the EDTA-P in MP (except Ap1 layer) and NP profiles and residual P (Red-P) in soil pedogenic horizons followed an opposite trend. With the increase of profile depth, the CaCl2-P/EDTA-P in the pedogenic horizons of the OP profile increased, which was significantly higher than that in the MP and NP profiles. The adsorption-desorption capacity of phosphorus in red paddy soil is mainly affected by SOM (soil organic matter), TP (total phosphorus), pH and iron-aluminum oxides. The interaction between SOM, TP, pH and iron-aluminum oxides jointly regulates the number of phosphorus adsorption sites and the strength of adsorption-desorption capacity in red paddy soil.【Conclusion】In this research, it was found that the Ap layer of red paddy soils was characterized by the weak capacity of the soil P sorption and strong capacity of P desorption and a high risk of soil P loss. Meanwhile, Br and C layers showed a stronger soil P sorption capacity and a weaker P desorption capacity, and a higher soil P fixation capacity than the Ap layer. Compared with the profile of OP, the exogenous P adsorbed in pedogenic horizons of NP and MP was more easily converted to the specialized adsorption state and residual state P, thus, resulting in a reduced risk of soil P loss. The risk of P loss in the OP profile was relatively higher than its counterparts, and timely regulatory measures are needed.

      • Composition Structure and Phosphorus Entrapment Capacities of Periphytic Biofilms in Paddy Fields in Different Regions in Eastern China

        LU Wen-yuan, SUN Peng-fei, XU Ying, LIU Jun-zhuo, WU Yong-hong

        DOI: 10.11766/trxb202203220002

        Abstract:

        【Objective】The periphytic biofilms widely distributed between the water-soil interface are key hot areas and necessary places for material migration and energy exchange in the paddy ecosystem. However, few studies have paid attention to the community characteristics and regulatory functions of the paddy periphytic biofilm. 【Method】In order to further understand the function of periphytic biofilm biological phosphorus capture, this study selects the periphytic biofilms in the main rice areas in China, covering three rice planting areas in the South China, the middle and lower reaches of the Yangtze River, and the Northeast. The composition and structure of periphytic biofilms communities are analyzed using high-throughput sequencing technology, combined with PLS-PM and regression analysis to reveal factors affecting the capture of phosphorus by periphytic biofilms around the paddy field. 【Result】There are significant differences in soil physical and chemical properties in different paddy regions (P < 0.05). The phosphorus capture capacity of the periphytic biofilms in main rice regions in China showed an increasing trend from north to south and west to east. There are significant differences in the composition of the periphytic biofilms community of paddy fields in different regions (P < 0.05). At the genus level, the periphytic biofilms in South China are dominated by prokaryotic microorganisms such as Acinetobacter and Proteiniclasticum and eukaryotic microorganisms such as Gregarina and Adriamonas. The periphytic biofilms in the middle and lower reaches of the Yangtze River are mainly prokaryotic microorganisms such as Bacillus and Cloacibacterium and eukaryotic microorganisms such as Gregarina and Vermamoeba. In the Northeast, periphytic biofilms are composed of prokaryotic microorganisms dominated by Flavisolibacter and Anaerolinea and eukaryotic microorganisms dominated by Adriamonas and Vermamoeba. It was found that the physical and chemical properties of soil (especially soil organic carbon and pH of floodwater) correlated with the diversity of the periphytic biofilms community. The microalgae in the periphytic biofilms in South China play a certain role in promoting the capture of phosphorus, while the phosphorus accumulating bacteria in the periphytic biofilms in the northeast have a positive effect on the capture of phosphorus. 【Conclusion】This study provides deep insight into the understanding of the composition and structure of the periphytic biofilms and their regulation in the phosphorus cycle in paddy fields through analysis of the phosphorus capture capacity of periphytic biofilms in paddy fields in different regions of China. Also, this study provides a theoretical basis for the future development of biotechnology to recycle surplus phosphorous in paddy fields.

      • Effects of Nitrogen and Phosphorus Addition on Organic Carbon Mineralization and Priming Effect in a Moso Bamboo Plantation Soil

        Yao Yihan, Zhang Shaobo, Zhou Jiashu, Liu Juan, Cai Yanjiang, Li Yongfu

        DOI: 10.11766/trxb202205060034

        Abstract:

        Abstract: 【Objective】Nutrients addition to soil have a significant effect on soil organic carbon mineralization. However, the response of soil organic carbon priming effect (PE) to the addition of different nutrients and its mechanism is still not clear.【Method】Urea and sodium dihydrogen phosphate were selected as exogenous nutrients and the effects of nitrogen addition, phosphorus addition and nitrogen combined phosphorus addition on soil organic carbon (SOC) mineralization, (PE), microbial function and soil physicochemical properties in a Moso bamboo plantation soil were investigated through an 80-day incubation experiment. 【Result】Nitrogen, phosphorus and their interaction significantly increased the cumulative CO2 emissions of native SOC mineralization (by 91.33%, 19.18% and 94.88%, respectively), resulting in a cumulative positive PE. The magnitude of positive PE induced by nitrogen and nitrogen combined with phosphorus was greater than that induced by phosphorus alone. The above three nutrient addition treatments all significantly increased soil pH, labile organic carbon pool (microbial biomass carbon, dissolved organic carbon and O-alkyl C), carbon-degrading enzyme (?-glucosidase and invertase) activities and cbhI and GH48 functional gene abundance, but inhibited the activity of polyphenol oxidase and RubisCO enzymes. Also, soil inorganic nitrogen content (NH4+-N and NO3--N) was enhanced under nitrogen and nitrogen combined phosphorus treatments but reduced under phosphorus treatment. Results of Spearman correlation analysis showed significant positive relationships between cumulative PE and soil pH, labile organic carbon, inorganic nitrogen content, carbon-degrading enzyme activities, cbhI and GH48 functional gene abundances, whereas the activities of polyphenol oxidase and RubisCO enzyme were negatively related to cumulative PE. 【Conclusion】The addition of nitrogen and phosphorus nutrients may have enhanced the rate of native SOC mineralization by affecting soil pH, the content of labile carbon and nitrogen, and stimulating the activity and function of microorganisms.

      • Advances in the Indicator and Assessment Approaches of Medium-low Yield Fields

        Bai Xueyuan, Zhang Jie, Cui Zhenling, Wang Guangjin, Lu Yujiao, Zhang Fusuo

        DOI: 10.11766/trxb202204070045

        Abstract:

        China’s medium-low yield fields are widely distributed and have great potential for land productivity improvement. Improving the land productivity of medium-low yield fields is of great significant for ensuring food security and achieving sustainable development goals (SDGs). Assessing the quality and spatial distribution of medium-low yield fields is the prerequisite and basis for land improvement. This paper systematically reviewed the concept, evaluation indicators, and main evaluation methods of medium-low yield fields. Based on the research status of medium-low yield fields, this paper discusses the main problems and development trends of the assessing of medium-low yield fields in China. The existing concepts of medium-low yield fields focus on the area and quality of medium-low yield fields, and there are few studies on ecological aspect and sustainable development abilities. Furthermore, the indicators system and evaluation methods for medium-low yield fields are not uniform. In the future, the medium-low yield fields assessment should consider quantity, quality, and ecology aspects. The medium-low yield fields assessment should be focused on the multi-scale assessment indices system construction and multi-source data fusion assessment methods innovation. Analyzing the spatial and temporal pattern of medium-low yield fields in different scales is helpful to explore ways to increase the productivity of green, high-yield, and efficient agricultural production, ensure food security, and promote the realization of SDGs

      • Distribution Patterns of Nitrifiers within Soil Aggregates under Different Cropping Systems

        Xia Weiwei, Li Yikun, Zhang Meng, Sun Xiangxin, Wang Yufang, Jia Zhongjun

        DOI: 10.11766/trxb202203220126

        Abstract:

        Abstract: 【Objective】 Nitrifiers play an important role in the process of farmland soil nitrogen transformation. A study on the distribution of nitrifying microorganisms in aggregates will help to reveal the interaction mechanism between soil structure, microorganisms and soil nutrient cycling. 【Method】The changes in soil aggregate properties and nitrification potential (NP) in maize monoculture (M-M) and maize peanut rotation (M-P) were compared, and the abundance and community composition of different nitrifying functional genes in soil aggregates were evaluated by quantitative PCR and high-throughput sequencing. 【Result】Compared with M-M, M-P significantly increased pH, NH4+ and total carbon (TC) in soil aggregates. M-P also significantly enhanced NP, but the aggregate size had no significant effect on NP. The abundance of the AOB amoA gene was higher in M-P and also more abundant in smaller aggregates. The distribution pattern of AOA and comammox amoA genes was opposite to that of AOB, indicating that AOB can better adapt to the micro-environment of smaller aggregates, while AOA and comammox tended to dominate in larger aggregates. In addition, compared with M-M, the difference in AOA/AOB and comammox/AOB ratio between M-P aggregates decreased, indicating that rotation promoted an even distribution of soil nitrifiers among different aggregate sizes. By further analysis of the nitrifying community based on the 16S rRNA gene sequencing, the results showed M-P increased the proportion of Nitrolancea-like NOB and Candidatus Nitrosocosmicus-like AOA, decreased the proportion of Nitrospira-like NOB, and had no significant effect on AOB compositions. The aggregate size only had a significant effect on the proportion of Nitrosospira-like AOB. NH4+ content and pH were the main factors affecting soil NP and the nitrifying microbial community structure among soil aggregates. NP was positively correlated with AOB amoA gene abundance and negatively correlated with AOA amoA gene abundance. However, in terms of community composition, Nitrosospira-like AOB, Candidatus Nitrosocosmicus-like AOA and Nitrospira-like NOB all showed positive correlations with NP.【Conclusion】Soil aggregate size and cropping system can greatly affect the distribution of nitrifying microorganisms in soil aggregates. However, nitrifying microorganisms have different adaptation mechanisms among aggregates. This study provides a theoretical support for improving the ecological adaptation mechanism of soil nitrifying microorganisms in the micro-environments under Gramineae-Legume rotation.

      • Correlation Between the Stability and Function of Soil Microbial Community Driven by Reductive Soil Disinfestation

        Zhaojun, Zhangjingqing, Linyulan, Wangbaoying, Huangxinqi, Zhangjinbo, Caizucong

        DOI: 10.11766/trxb202205150254

        Abstract:

        【Objective】Reductive soil disinfestation (RSD) is an effective agriculture practice to conquer continuous cropping obstacles by the elimination of soil-borne pathogens, degradation of allelochemicals, improvement of soil microbial community structure, and restoration of soil microbial functions. However, the effects of RSD practice on the stability of the mono-cropped soil microbial community are still unknown. Moreover, the relationship between soil microbial community stability and functions also needs to be studied. Therefore, this study was oriented to explore the relationship between the stability and function of soil microbial communities driven by reductive soil disinfestation. 【Method】A field experiment, designed to have four treatments, i.e. CK (control without soil treatment); SB (RSD incorporated with 15 t·hm-2 organic substrate with C/N ratio of 122); BD (RSD incorporated with 15 t·hm-2 organic substrate with C/N ratio of 19); and SB+BD (RSD incorporated with 15 t·hm-2 organic substrates containing both high and low C/N ratios with equal mass), was carried out in a lisianthus mono-cropped soils in Shiping County, Yunnan Province. Biolog microplate method, quantitative real-time PCR, and high-throughput sequencing were used to analyze the microbial community stability, microbial metabolic activity and function diversity, and the abundance of nitrogen-related functional genes. 【Result】Results showed that RSD significantly reduced the stability of bacterial community composition and abundance as compared to CK, with the effects of SB+BD treatment being stronger than that of SB and BD treatment, whereas it had no significant effect on the stability of fungal community composition and abundance. Also, RSD significantly enhanced the stability of interactions between bacterial and fungal communities, and SB and BD treatments had greater effects on the improvement of stability of the interaction between microbial communities than SB+BD treatment. Regression analysis indicated that the stability of interaction relationship of soil microbial community was closely related to the stability of microbial composition and abundance. In addition, correlation analysis showed that soil microbial community stability was highly correlated with its activity, carbon metabolic function and denitrification capacity. 【Conclusion】Collectively, reductive soil disinfestation can improve the stability of interactions between microbial taxa by reducing the stability of microbial community composition and abundance, thereby promoting the restoration of soil microbial activity and improvement of community ecological function.

      • Effects of a New Rice-Shrimp Farming Model on Soil Fertility and Microbial Community Structure in Paddy Field

        Lai Zheng, Xiao Liting, Lai Sheng, Yang Huiling, Ni Caiying, YANG Wenjing, JIAN Min-fei

        DOI: 10.11766/trxb202205150255

        Abstract:

        Abstract: 【Objective】 This study was designed to explore the impact of a new rice-shrimp farming model(NRS) on soil fertility and microbial community composition in paddy fields. 【Method】Three different farming treatments: new rice-shrimp farming model (NRS), traditional rice-shrimp farming model (TRS) and rice monoculture (CK) were set up, with CK as control. The paddy soil physicochemical indexes and microbial diversity and community structure were determined by using the soil agrochemical analysis method and 16S rDNA amplicon high-throughput sequencing technology. 【Result】 Compared with CK and TRS, NRS significantly improved the contents of soil organic matter, available K, available P and pH. NRS significantly increased the microbial diversity and species richness. A total of 32 phyla, 80 classes, 202 orders, 347 families and 491 genera of bacterial groups were detected in the paddy soils of three models. The dominant bacterial phyla were Proteobacteria, Acidobacteriota, Chloroflexi, Verrucomicrobiota and Desulfobacterota. Compared with CK, NRS changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Acidobacteria, Chloroflexi and Verrucomicrobiota were increased by 30.89%, 36.38% and 2.16%, while the relative abundance of Proteobacteria and Desulfobacteria decreased by 17.96% and 58.59%, respectively. Compared with TRS, NRS also changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Desulfobacteria increased by 14.93%, while the relative abundance of Chloroflexi, Verrucomicrobiota, Proteobacteria and Acidobacteria decreased by 39.29%, 37.42%, 16.27% and 6.81%, respectively. Correlation analysis showed that soil organic matter, available potassium, available phosphorus, available nitrogen and pH were the main physicochemical factors affecting the structure of soil microbial community in paddy fields. 【Conclusion】 The new rice-shrimp farming model is conducive to improving soil fertility, significantly improving soil microbial diversity and altering microbial community structure. The results of this study have certain guiding significance and reference for the demonstration and promotion of the new rice-shrimp farming model.

      • Impact of Sample Size and Sampling Method on Accuracy of Topsoil pH Prediction on A Regional Scale

        SUN Yueqi, SUN Xiaomei, WU Zhenfu, YAN Junying, ZHAO Yanfeng, CHEN Jie

        DOI: 10.11766/trxb202112010651

        Abstract:

        【Objective】Under the background of high-intensity soil resource utilization, digital soil mapping has become an effective method to obtain and characterize soil information quickly, efficiently and accurately. The accuracy and reliability of soil spatial prediction and digital mapping are restricted by multiple factors, such as soil sample size, sampling strategy, prediction model, the complexity of geomorphology and soil-forming environment in the target region, and quality of covariate data. 【Method】Choosing Henan Province as the study region, we applied five of the most representative machine learning (ML) algorithms to spatially predict and digitally map the topsoil pH of croplands. Afterwards, the impact of different sample sizes and sampling methods on the performance of the chosen ML models and the prediction accuracy of topsoil pH were compared. 【Result】The results showed that: (1) When the soil sample size increased from 200 to 2 000, the performance of all ML models and prediction accuracy of topsoil pH showed a general trend of rapid increase regardless of the sampling method. When sample size reached and exceeded 2 000, the performance of most ML models tended to be stable, and the prediction accuracy of topsoil pH increase rapidly slowed down, suggesting that a soil sample size of 2 000 might be the sample size threshold for these ML models to predict the topsoil pH of croplands in this area. (2) The performance of the five ML models and their topsoil pH prediction accuracy was significantly different. The tree-based ML models, namely Random forests (RF) and Cubist performed best. No matter which sampling method was used, when the sample size was more than 2 000, the archived coefficient of determination (R2) of the two models could be stable between 0.75 and 0.80, and the RMSE could be kept below 0.50. (3) When the soil sample size was large enough, the sampling method had little impact on the ML model performance. Also, the topsoil pH prediction accuracy and the sampling method gradually highlighted when the soil sample size was less than 2 000. Comparatively, Conditioned Latin hypercube sampling (clhs) had advantages when the sample size was small. When the sample size was 1 000, clhs sampling method could still keep the R2 of random forest and Cubist prediction at about 0.80. Even when the sample size was as small as 200, the R2 archived by all five ML models under the clhs sampling method was above 0.54. (4) The uncertainty analysis showed that 73.9% of the observed values of topsoil pH of the validation samples fell into the 90% Prediction Interval (PI) of the random forest model, indicating that the reliability of the model was slightly overconfident, but it was within the acceptable range. In addition, the data indicated that the uncertainty of model prediction was not significantly correlated with sample size. 【Conclusion】Tree-structured machine learning models Random Forest and Cubist stand out in this case. Improving the spatial prediction and digital mapping accuracy of soil target variables cannot be achieved simply by expanding the scale of sample points and increasing the density of sample points. It is necessary to improve the model prediction performance and covariate data quality at the same time. When the sample size is large enough, the sampling strategy has little effect on the performance of the ML model and the prediction accuracy of surface soil pH; when the sample size is smaller than a certain threshold, the sampling method has a significant impact on the model performance and prediction results.

      • Research Progress of Heavy Metal Biomineralization Induced by Iron and Manganese-Oxidizing Bacteria in Soils

        WU Chuan, LUO Yuxuan, XUE Shengguo, QIAN Ziyan, QI Yanting

        DOI: 10.11766/trxb202201070648

        Abstract:

        The effects of iron-manganese oxidizing bacteria-induced mineralization on the environmental behavior of heavy metals were reviewed, including iron/manganese-oxidizing bacteria and biomineralization, iron/manganese-oxidizing bacteria-induced iron-manganese oxide precipitation coupled with heavy metal stabilization, and the effect of iron-manganese oxide on heavy metals in soils. The application of iron/manganese-oxidizing bacteria in the bioremediation of different heavy metals was further summarized from the aspects of the biological mineralization pattern of iron/manganese-oxidizing bacteria (direct or indirect catalytic mineralization of iron oxide protein/enzyme, dual electron transfer reaction of manganese oxidase dominated by polycopper oxidase and the mineralization induced by external factors), heavy metal stabilization mechanisms of iron/manganese-oxidizing bacteria biological mineralization in soils (precipitation/coprecipitation, adsorption/complexation and redox). The effects of extracellular polymers, temperature and pH, coexisting ions and other factors on the mineralization process were also analyzed, in order to provide theoretical references for microbial-induced mineralization to remediate heavy metal pollution. Future work should focus on the long-term stability of heavy metals generated by minerals, the regulation of different microbial species combinations on mineralization, and the application of iron/manganese-oxidizing bacteria in the remediation of soil multi-heavy metal contaminated sites.

      • Effects of Nitrite Addition on Transcription Activity of Nitrification and Denitrification Functional Genes and N2O Emission in Soil

        CHEN Jiji, JING Hongwei, CAO Wenchao, TAO Lei, WANG Jingguo

        DOI: 10.11766/trxb202107190370

        Abstract:

        【Objective】Studies relating soil N availability to N2O emissions commonly focus on NO3- and in some cases NH4+. Thus, less effort has been devoted to measuring soil NO2- despite its role as a central substrate in N2O production. 【Method】In this study, two typical greenhouse vegetable soils (alkaline vs. acid soil) were selected to explore the influencing mechanism of NO2- on N2O emission. Also, its association with the inorganic nitrogen transformation processes, gaseous emission (N2O, N2, CO2), and the abundances and transcription copies of functional genes (amoA, nirK, nirS and nosZ) under anaerobic (0% O2) and aerobic (21% O2) conditions through in-lab incubation and real-time quantitative polymerase chain reaction (qPCR).【Result】The natural accumulation and tolerance of NO2- were higher in alkaline soil than in acidic soil. With respect to pH, the relative concentration of NO2- in soil did not correlate with N2O emissions. However, the addition of NO2- significantly increased the N2O emission and N2O/(N2O+N2) index (IN2O) of the two soils (P<0.05), and decreased the N2 emission in both soils under anaerobic conditions (50.9% and 94.2% in alkaline and acidic soils, respectively). In the alkaline soil, exogenous NO2- at 60 mg?kg-1 had no significant inhibition effect on soil CO2 emission, and the transcription copies of nirK gene at 16 h under anaerobic incubation, amoA gene at 16 h and nirS gene at 84 h under aerobic incubation were significantly higher than that of control check (N0), but nosZ gene had no such phenomenon. In acid soil, the overall gene and transcription activity of amoA was low, and the transcription copies of the nirS gene increased with the increase of incubation time in aerobic N0 treatment (P<0.05). Exogenous NO2- at 60 mg?kg-1 significantly reduced the CO2 emission, and the abundance and transcription copies of related genes in the acid soil. Oxygen significantly reduced the transcription copies of denitrification functional genes in both soils, and nirK was more sensitive. Compared with the N0 treatment under anaerobic incubation, the transcription copies of nirK, nirS and nosZ in alkaline soil were reduced by 97.3%, 74.5% and 89.0%, respectively, at 16 h under aerobic incubation. The variation trend of the denitrification genes transcription copies in both soils under aerobic conditions was different. In the alkaline soil, the transcription copies of denitrification functional genes were significantly decreased with the increase in incubation time (P<0.05). In the acidic soil, only nirK transcription copies decreased significantly with the increase of incubation time (P<0.05) in N0 treatment under aerobic conditions, while nirS and nosZ transcription copies increased, or decreased first and then increased, respectively. 【Conclusion】The accumulation of NO2- in soils will increase soil IN2O and affect the N2O emission pathway by inducing nir gene transcription to compete for electrons with N2O reductase and inhibiting N2O reductase activity. These results provide a scientific basis for exploring the efficient utilization of soil nitrogen and N2O reduction in greenhouse vegetable soils.

      • The Change in Dominant Mycorrhizal Fungi Type Induced by Stand Transformation Affects Soil Organic Carbon Accumulation

        TU Jiaying, JIN Wenhao, SHENG Weixing, XING Jiajia, PENG Liyuan, CHEN Junhui, XU Qiufang, QIN Hua

        DOI: 10.11766/trxb202206210271

        Abstract:

        【Objective】Masson pine forest(Pinus massoniana Lamb.)is a typical ectomycorrhizal (ECM) dominant forest. However, in recent years, the ecological service function of the Masson pine forest decreased due to pine wood nematode disease, and the Masson pine forest was gradually replaced by an Arbuscular mycorrhizal (AM) dominant broadleaved forest. However, it remains unclear what influence could be exerted by the changes of dominant mycorrhizal types on soil organic carbon accumulation during the conversion of Masson pine forest to broadleaf forest in the subtropical region.【Method】In this study, the biomass of ECM fungi and AM fungi were determined by high-performance liquid chromatography (HPLC) and neutral lipid fatty acids (NLFA), respectively. At the same time, phospholipid fatty acids (PLFAs) technology was used to study the characteristics of the microbial community. The content of glomalin-related soil protein (GRSP) and the activities of soil extracellular enzymes was also determined in Masson pine and broadleaved forests in Jiande County, Zhejiang Province.【Result】The results showed that: AM fungi-dominated (AMD) broadleaved forest replaced ECM fungi-dominated (ECMD) Masson pine forest, soil organic carbon in AM fungi dominated broadleaved forest was significantly enhanced by 36.81%, microbial carbon use efficiency (CUE) significantly increased by 53.85%, and AM fungal biomass significantly increased by 25.57%. Moreover, compared with ECM fungi-dominated forests, the biomass of ECM fungi in AM fungi-dominated forests decreased significantly by 45.04%. The Masson pine forest, which was dominated by ECM fungi, was subjected to more severe microbial nitrogen limitation. Phospholipid fatty acids analysis showed that the gram-positive bacteria (G+) and the ratio of gram-positive bacteria to gram-negative bacteria (G+/G-) in Masson pine forest dominated by ECM fungi compared with the broadleaved forest dominated by AM fungi were significantly decreased by 21.47% and 6.46%, respectively. Redundancy analysis (RDA) results showed that there were significant differences in microbial community structure between forests dominated by AM fungi and ECM fungi (P<0.05), in which AM fungal biomass (R2=0.48, P=0.002) and soil organic carbon content (R2=0.47, P=0.003) were significantly correlated with the variation of microbial community structure (P<0.05).【Conclusion】The decrease of GRSP and the different recruit of microbial groups by different mycorrhizal fungi types were important reasons for the reduction of soil organic carbon content in forests dominated by ECM fungi compared to AM fungi dominated forests. Therefore, the substitution of broadleaved forest for Masson pine forest in the subtropical region increased the content of forest soil organic carbon and improved the function of the forest carbon sink.

      • Effects of Shrub Encroachment on Soil Organic Carbon Components in Qinghai-Tibetan Alpine Grassland

        ZHANG Dong, LIU Jinqiu, MA Wenming, WANG Changting, DENGZENG Zhuoma, ZHANG Ting

        DOI: 10.11766/trxb202203220004

        Abstract:

        【Objective】Changes in the dominant vegetation community will inevitably affect soil organic carbon (SOC) by altering the quantity of litter and root exudates during shrub encroachment. Thus, this study aimed to explore the response of different active organic carbon fractions in alpine grassland soils to invasion by different shrub species.【Method】Physicochemical fractionation method was used to divide soil organic carbon into non-protected carbon, physically-protected carbon, chemically-protected carbon and biochemically-protected carbon. It was analysed the contents of various organic carbon fractions and factors influencing their contents among four typical shrub-grassland and unshrub-encroached grassland on the east edge of Qinghai-Tibetan Plateau.【Result】The results showed that (1) Shrub encroachment has no significant effect on the SOC content of the surface soil (0-10 cm) in alpine grassland (P>0.05), but the content of organic carbon components was different. After Spiraea alpina and Sibiraea angustata shrubs encroached the grassland, the non-protected organic carbon and biochemically-protected organic carbon contents were significantly decreased (P<0.05) while the non-protected organic carbon content significantly decreased when Potentilla fruticose encroached the grassland. Also, the contents of physically-protected and chemically-protected organic carbon decreased significantly in Caragana microphylla encroached grassland (P<0.05), while the biochemically-protected organic carbon increased significantly (P<0.05). (2) SOC in both grassland and shrub patches soil were dominated by non-protected carbon pool, followed by resistant carbon pool (chemically-protected organic carbon and biochemically-protected organic carbon), while physically-protected organic carbon pool accounted for the least. (3) The contents of soil clay and total nitrogen were the main factors affecting the organic carbon fractions in alpine shrub-encroached grassland, with an explanation degree of 51.2%. 【Conclusion】The invasion of different shrub species had inconsistent effects on the content of different reactive organic carbon fractions. The soils of both unshrub grassland and shrub sample sites on the Tibetan Plateau were dominated by non-protected carbon. Thus, in the presence of external disturbances, the organic carbon pool in the area may become a source of carbon.

      • Research on the Carbon Sink Contribution of Subtropical Paddy Field Soil Under Different Straw Return Rates

        LUO Yuye, QIU Longxia, LONG Jun, CHEN Hanyue, WU Ting, LI Jing, XING Shihe, ZHANG Liming

        DOI: 10.11766/trxb202112280700

        Abstract:

        【Objective】Straw returning is generally considered to be an effective way to increase soil "carbon sink" and mitigate climate change. China is rich in straw resources, but the rate of straw returning to the field is less than 20%, which is the main reason for a long-term deficit of carbon pool in farmland soils in China. There are many kinds of straw resources in subtropical region, which also account for about 30% of the total output of the country. Therefore, clarifying the quantitative relationship between the amount of straw returning and soil carbon sink in subtropical areas of China is an important basis for formulating carbon sequestration measures and implementing national strategies such as carbon neutralization.【Method】Paddy soil in Fujian Province, a typical subtropical region in China, was selected as our study area. The spatial database was constructed by the digitization of 1:50,000 soil map paper data from 84 counties (cities and districts) in Fujian Province during the second soil census in 1982. The soil attribute database is composed of 15,833 surface samples from the arable land fertility survey conducted by the Ministry of Agriculture and Rural Areas in 2016. ArcGIS software and the PKB method (Pedological Knowledge-Based Method) connect the spatial data and attribute data in a 1:50 000 soil database. Using the latest established 1:50000 soil database and DNDC (DeNitrification and DeComposition) model widely used in the agricultural ecosystem, the future dynamic changes of soil organic carbon under different rates of straw returned in Fujian Province were simulated.【Result】 Results showed that the average annual carbon sequestration rates can reach 173, 302, 478 and 838 kg·hm-2 , and the sequestration of carbon amounts were 11.56, 20.15, 31.90 and 55.95 Tg during the period of 2017-2053 under the treatments of conventional management (15%), straw returning of 30%, 50%, and 90%, respectively. Straw was returned to the field from the perspective of carbon sequestration rate, the average annual carbon sequestration rates of Acid sulfate paddy soils and Salinized paddy soils were the highest, which ranged from 220 to 920 kg·ha-1 under different straw returning rates. In terms of total carbon sequestration, the total carbon sequestration of Percogenic paddy soils and Hydromorphic paddy soils under different straw returning rates accounted for 81% of the total carbon sequestration over the whole province. Considering the administrative areas, the average annual carbon sequestration rate and total amount in Longyan and Quanzhou were relatively large, ranging from 202~937 kg·hm-2 and 1.55~8.34 Tg under different straw returning rates, respectively.【Conclusion】In general, the increase in straw returning ratio contributed significantly to the "carbon sink" of paddy soil in Fujian Province, which is worth promoting. However, under different straw returning rates, due to the influence of soil properties, climate, fertilization and other factors, the contribution of different soil subtypes and administrative regions in Fujian Province to carbon sequestration varies greatly. In the future, it is necessary to formulate reasonable management measures for carbon sequestration and emission reduction for different soil types and prefecture-level cities.

      • Effects of Root, Stem and Leaf of Maize Enriched by 13C on Brown Earth

        Yu yaxi, PEI Jiu-bo, LIU Wei, WANG Meng-meng, YIN Si-jia

        DOI: 10.11766/trxb202110300587

        Abstract:

        Due to the differences in carbon chemical components among maize residues (root, stem and leaf), their return to cropland soils with different fertility levels will induce differences in soil respiration and priming.【Method】In order to explore these differences in the field, a 540-day in-situ field experiment with eight treatments of low fertilizer soil (LF+CK), low fertilizer soil + root (LF + R), low fertilizer soil + stem (LF + S), low fertilizer soil + leaf (LF + L), high fertilizer soil (HF+CK), high fertilizer soil + root (HF + R), high fertilizer soil + stem (HF + S) and high fertilizer soil + leaf (HF + L), was carried out at a long-term positioning station of brown earth in Shenyang Agricultural University using 13C labeled maize straw tracing method.【Result】Results showed that (1) the contribution rates of soil respiration flux and straw carbon to soil CO2-C emission showed downward trends over the in-situ incubation period. (2) Compared to the treatment without straw, the cumulative CO2-C released from low fertility soil with root, stem and leaf increased by 134%, 126% and 95%, respectively, while that from high fertility soil increased by 157%, 189% and 96%, respectively. (3) The contributions of root and stem to soil CO2-C emission in high fertility soil were significantly greater than that of leaf, but there was no difference in low fertility soil. (4) Different parts of maize straw returning to the field could cause the positive priming effects in both high and low fertility soils. Meanwhile, the priming effects of adding root and stem were significantly stronger than that of adding leaf, showing root and stem would cause more positive priming effects of soil CO2-C than the leaf. Moreover, there was no significant effect on the priming effect between straw parts and soil fertility.【Conclusion】Overall, this study enriched the theory of cropland soil respiration induced by straw returning, suggesting that the interaction of straw parts and soil fertility on soil respiration should be considered in straw returning.

      • Soil Organic Matter Prediction Research on the Integrating Models with Reduction of Residual Autocorrelation

        SONG Jie, WANG Siwei, ZHAO Yanhe, YU Dongsheng, CHEN Yang, WANG Xin, FENG Kaiyue, MA Lixia

        DOI: 10.11766/trxb202111020591

        Abstract:

        【Objective】Improving the spatial prediction accuracy of soil attributes is of great significance for achieving accurate fertilization of farmland and protecting the ecological environment. 【Method】Soil organic matter (SOM) data was collected from 1773 samples from soil surface layer (0-20cm) of cultivated land in Luanping County, Hebei Province. The optimal environmental variables were screened through a stepwise regression analysis method. Multiple linear regression (MLR), ordinary kriging (OK), random forest (RF), Bayesian regularized neural network (BRNNBP), and the corresponding three integrated models combined with a geostatistical model (MLR-OK, RF-OK and BRNNBP-OK) were utilized to predict SOM content via the training set including 1426 sampling points. Also, the prediction accuracy of each method was compared with 347 sampling points of the testing set. Autocorrelation analysis was carried out based on the residual of the integrated model to evaluate the fitting effect of the model. 【Result】Results showed that the range of SOM content in the study area was 8.62~35.64 g·kg-1, and the coefficient of variation was 20.26%, which showed a moderate spatial variation. High concentrations of SOM were mainly distributed in the northeast and southeast areas with higher altitudes, while relative low concentrations of SOM were mostly observed in the southwest and central valleys of the study area. Elevation, slope and temperature selected by stepwise regression were closely related to SOM content (P<0.001). The lowest average absolute error and the root mean square error of the BRNNBP-OK model were 2.162 g·kg-1 and 2.801 g·kg-1, respectively. Compared with the OK, MLR, RF, BRNNBP, MLR-OK and RF-OK models, the goodness of fit of the BRNNBP-OK model increased by 1.81%~30.42%, making it an optimal model for SOM spatial prediction. Compared with the single model, the nugget coefficient of the integrated model residual was greater than 0.75, and the Moran"s I was less than 0 and numerically closer to 0, indicating that the spatial autocorrelation of the integrated model residual was weakened and the residual presented a more discrete spatial distribution. At the same time, the accuracy of all models was significantly correlated with Moran"s index of model residuals. 【Conclusion】In this study, the integrated model fitted more trends and the spatial aggregation of model residuals decreased and even tended to be discrete. Thus, the overall prediction accuracy of the integrated models was improved.

      • Effects of Biocrusts on Dustfall Retention and Soil Fixation and Their Influencing Factors in the Chinese Loess Plateau

        CAO Yousong, XIAO Bo, LI Shenglong, WANG Yanfeng, YU Xingxing

        DOI: 10.11766/trxb202112150675

        Abstract:

        【Objective】 Wind activity and aeolian dust transportation are key terrestrial processes in dryland ecosystems. Biocrusts are photoautotrophic communities that consist of cyanobacteria, actinomycetes, mosses, green algae, fungi, and other organisms. As an important living skin and pioneer communities developing on surface soil in drylands, biocrusts strongly influence most soil processes (hydrological, ecological, biological, and chemical processes) and have a variety of essential ecological functions. Although biocrusts are usually relatively thin (a few millimeters or centimeters at most), these organisms have unique micro-structures which could positively influence the formation of aeolian soil parent material. In order to further explore the aeolian sedimentary effects of biocrusts on soil parent material, we conducted this study to understand the effects of biocrusts on dustfall retention and soil fixation, as well as their influencing factors.【Method】 In the north of Chinese Loess Plateau, the biocrusts developed on aeolian and loessal soils were sampled, and the analyses and simulated experiments were carried out in the laboratory. The amount of dustfall retention and soil fixation of biocrusts at different developmental stages (cyano crust, mixed crust, and moss crust) were measured. The variations of dustfall retention amount under different wind speeds, dustfall grain sizes, and dustfall amount were explored. We also explored the key influencing factors.【Result】 The dustfall retention amount of biocrusts was 1.1~4.8 times higher than that without biocrusts, and it increased with the developmental stages of biocrusts from cyano crust to moss crust. On average, the erosion reduction of biocrusts was 19.5~4892.7 t·km-2·a-1 under 1~8 m·s-1 wind speeds. Moreover, the dustfall retention amount increased with increasing soil water content, and these increases were positively correlated with wind speed. It was found that the dustfall retention amount was increased by 4.9%, 53.1%, 59.6%, and 72.3%, respectively, under 5~8 m·s-1 wind speeds when relative water content increased from 0 to 80%. Additionally, the dustfall retention amount was also significantly and positively correlated with the surface roughness of biocrusts. Similarly, the soil fixation amount of biocrusts also increased along with their developmental stages from cyano crust to moss crust. The soil fixation amount of moss crust was 1.4 times higher than that of cyano crust. At the same developmental stage, the soil fixation amount of biocrusts on aeolian sandy soil was significantly (F=30.74, P<0.003) higher than that on loessal soil. Furthermore, the soil fixation amount was positively correlated with the thickness of biocrusts and negatively correlated with the surface roughness. It firstly increased and then decreased with increasing soil water content.【Conclusion】 These findings show that biocrusts can significantly retain dustfall and fix soil due to their root, mycelium, exudates, and pore structures, and these biocrust functions are of great significance for the aeolian sedimentary process of soil parent material, the pedogenic process of primitive soil, and the primary succession of dryland ecosystem in the Chinese Loess Plateau. Additionally, this study demonstrates the important effects of biocrusts on the formation of aeolian soil parent material, and their key influencing factors are surface roughness, developmental stages, and water content of biocrusts. Therefore, it is essential to pay attention to the biocrust effects on dust retention and soil fixation in arid and semiarid climate regions.

      • Characteristics and Correlation of Fusarium oxysporum and Soil Nutrients around Banana Roots

        LIU Zexian, WANG Beibei, TAO Chengyuan, Ou Yannan, LV nana, SHEN Zongzhuan, LI Rong, SHEN Qirong

        DOI: 10.11766/trxb202112050660

        Abstract:

        【Objective】This study aimed to elucidate the characteristics and correlations between Fusarium oxysporum and soil nutrients in banana orchards with Panama wilt occurring through analyzing the number of F. oxysporum and nutrient contents in soils. This can provide a certain theoretical basis for the prevention and control of banana Panama wilt.【Method】Nine symptomatic and nine non-symptomatic banana plants in each orchard from 15 banana orchards in the main banana production areas in China and Laos were randomly selected for soil sample collection. Then real-time quantitative PCR and soil agrochemical analysis were used to explore the abundance of F. oxysporum and nutrient contents in the 270 sampled soils.【Result】The result showed that the abundance of F. oxysporum in the soil sampled near the symptomatic banana roots was significantly higher than that collected near the non-symptomatic banana roots, with an average copy of 5.5 as lg-transformed per gram of dry soil. However, there were almost no significant differences between the nutrient contents of soils sampled from symptomatic and non-symptomatic banana plants. The distribution of various indexes of soil nutrients in the studied banana orchards was different based on each factor. Among them, only the contents of organic matter and total phosphorus were distributed normally while the soil pH, and contents of total nitrogen and zinc were skewed normal distribution. Mantel test results further displayed that the overall soil nutrients were significantly correlated to the abundance of F. oxysporum. Specifically, the soil pH, and contents of iron, manganese, and copper were significantly and negatively correlated to the abundance of F. oxysporum revealed by the Spearman correlation analysis between the abundance of F. oxysporum and each soil nutrient. In addition, the correlation analysis between F. oxysporum and nutrients in soils with different degrees of acidity and different organic matter contents showed that in the weakly acidic banana garden soil (pH > 6.0), the number of F. oxysporum in soils was significantly negatively correlated with the contents of iron, manganese and copper. Meanwhile in soils where organic matter contents were not seriously lacking (> 1%), the abundance of F. oxysporum in soils displayed a significant negative correlation with soil pH and the contents of iron, manganese, copper and zinc.【Conclusion】In summary, banana orchards in the main banana production areas in China and Laos usually exhibit an acidification trend. Symptomatic banana soil showed an increase of F. oxysporum with a negative correlation to soil pH and the contents of trace elements, especially iron, manganese, copper and zinc.

      • Incorporation of Carbon and Nitrogen from Rice Straw into Particulate Organic Matter in Black Soil with Rice Planting

        Wu Yihui, Wagn hongfei, Zhang Rui, An Jing, zhangyuling, Yu Na, Zou Hongtao

        DOI: 10.11766/trxb202203030009

        Abstract:

        【Objective】Particulate organic matter is an important component of soil labile organic matter and a sensitive index to evaluate a change of the soil organic matter. The climate in Northeast China is very cold, so, paddy fields therein have a short flooding period and a long non-flooding period since the soil is frozen for most of the time. However, little research has been carried out on the incorporation of exogenous rice straw carbon (C) and nitrogen (N) into particulate organic matter in black soil with different rice planting years. 【Methods】A 300-day incubation experiment was conducted, in which dual-isotope-labeled (13C/15N) rice straw was added to a cultivation chronosequence of paddy soils ranging from 0 to 85 years (0 a, 12 a, 35 a, 62 a and 85 a). Flooding incubation experiments were conducted at a temperature of 20 °C and a 1 cm water-flooded layer in a laboratory for 150 days while the freezing incubation experiments were also carried out for 150 days under a soil temperature of -15 °C and water-saturated. 【Result】 Throughout the entire incubation period, the contents of particulate organic carbon (POC) and particulate organic nitrogen (PON) in all paddy soils from the samples with and without rice straw were lower than that in the control soil (0 a). The contents of POC and PON in all soils from the samples with rice straw increased after 5 days of flooding incubation, but they did not show a consistently increasing trend in the subsequent incubation period. For paddy soils of different rice planting years, the relative contribution of the added rice straw C (N) to POC (PON) was 0.2%-13.9% (0.4-3.8%). 0.7%-13.8% (1.4%-9.9%). At the end of freezing incubation, incorporation of the rice straw C into POC in control soil (0 a) and 12-year paddy soil (12 a) decreased significantly compared with that at the end of flooding incubation. Also, the added rice straw N into PON in control soil (0 a) and 85-years paddy soil (85 a) decreased while the added rice straw C (N) into POC (PON) in other rice cultivating years was still increasing. The incorporation of the added rice straw C into POC was significantly negatively correlated with soil organic C, total N and alkaline N, and significantly positively correlated with soil C/N, available phosphorus and microbial biomass C. In addition, the incorporation of straw N into soil PON showed a significant negative correlation with soil organic C content. 【Conclusion】The study showed that the longer the years of rice planting in a typical black soil of northeast China, the contents of soil organic C, total N and alkaline N were relatively low, while the soil C/N, available phosphorus and microbial biomass C contents were relatively high. The greater the incorporation of straw C and N into soil particulate organic matter, the more the response of soil particulate organic matter to rice straw addition.

      • Effects of environmental factors on rate and partitioning of dissimilatory nitrate reduction processes in paddy soils

        Jin Ke, Wei Zhijun, Ma Xiaofang, Li Chenglin, Shan Jun, Yan Xiaoyuan

        DOI: 10.11766/trxb202203090101

        Abstract:

        【Objective】Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are the two competing nitrate reduction pathways that remove the available nitrate, both of which are affected by inter-related environmental factors. Understanding how environmental factors regulate nitrate partitioning in these two competing processes is of great significance for the optimization of nitrogen management in paddy fields.【Method】Using 15N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), a series of laboratory incubation experiments were performed to investigate the effects of different environmental factors including temperature (5, 15, 20, 25, and 35 ℃), pH (5, 6, 7, 8.5, and 9.5), NO3– concentration (50, 100, 150, 200, and 300 μmol·L–1), C/N (0, 2.5, 5, 12, and 30), Fe2+ (0, 300, 500, 800, and 1000 μmol·L–1), and S2– (0, 50, 62.5, 100, and 125 μmol·L–1) on denitrification and DNRA rates and their partitioning in nitrate reduction in three paddy soils (Wuchang, WC; Changshu, CS; Ya’an, YA).【Result】Denitrification was the predominant pathway ( 87.97%?91.73%), whereas DNRA only contributed to 8.27%~12.03% of the total dissimilatory nitrate reduction in all treatments. Denitrification and DNRA rates increased exponentially with increasing temperature, as well as the DNRA/(Denitrification + DNRA) (RDNRA). The highest denitrification and DNRA rates occurred at the pH of 7 and 8.5, respectively, and RDNRA was higher in an acidic environment (6.24%?15.56%) than under an alkaline environment (4.92%?14.67%). The response of denitrification and DNRA rates to nitrate concentrations fitted well with the Michaelis-Menten relationship, in which the Vmax and Km of denitrification were larger than those of DNRA. In the three paddy soils, compared with the treatment without glucose addition, denitrification rates were significantly increased by 22%?35% at the C/N ratio of 2.5. Following the C/N ratio increased to > 2.5, DNRA rates were enhanced by 74%?199%. In terms of Fe2+ and S2– addition treatments, denitrification rates were the highest in the low levels of electron donors (300?500 μmol·L–1 Fe2+ and 50?62.5 μmol·L–1 S2–), whereas more electron donors (800?1000 μmol·L–1 Fe2+ and 100?125 μmol·L–1 S2–) were required when DNRA reached the peak rates.【Conclusion】By exerting different effects on rates of denitrification and DNRA, temperature, pH, NO3–, C/N ratio, Fe2+, and S2– concentration significantly changed the partitioning between denitrification and DNRA. Specifically, relatively high temperature, C/N, Fe2+, and S2– concentration favored nitrate partitioning to DNRA, while denitrification dominated the nitrate reduction process in environments with a relatively high NO3– concentration. Collectively, our results provide comprehensive information in terms of regulation of environmental factors on nitrate partitioning between DNRA and denitrification in paddy soils. This deepens our understanding of nitrate reduction processes and provides a scientific basis for increasing nitrogen use efficiency by favoring the nitrate partitioning to DNRA in rice fields.

      • Variations in the Diversity and Community Assembly of Arbuscular Mycorrhizal Fungi in Greenhouse Soils during the Growing Season

        LIU Lei, XIAO Guangmin, WANG Ling, RU Shuhua, ZHANG Guoyin, SUN Shiyou

        DOI: 10.11766/trxb202204210197

        Abstract:

        Abstract: 【Objective】This study aimed to understand the key processes that drive the changes in diversity and community assembly of arbuscular mycorrhizal (AM) fungi in greenhouse ecosystem. 【Method】Soil samples were collected during different growth stages (i.e., fallow period, flowering stage, fruiting stage) of tomatoes in a greenhouse. Illumina MiSeq high-throughput pyrosequencing was performed to investigate the changes in taxonomic and phylogenetic diversity and community structure of AM fungi. The relative importance of stochastic and deterministic processes in structuring AM fungal community at different growth stages was analyzed by phylogenetic structure analysis. 【Result】Results showed that both taxonomic and phylogenetic diversity of AM fungi varied significantly across different growth stages. Compared with the fallow period, OTU richness, Shannon diversity, Pielou evenness, phylogenetic diversity (PD) and mean pairwise phylogenetic distance (MPD) of AM fungi significantly decreased by 42.82%~59.18%、43.25%~48.31%、17.46%~25.40%、57.14%~67.86% and 50.00%, respectively, during the flowering and fruiting stages. In addition, the relative abundance of Glomus was promoted in the growing period, whereas the relative abundance of Claroideoglomus and Paraglomus decreased. Also the relative abundance of Archaeospora followed a unimodal pattern. Results of permutational multivariate analysis of variance (PERMANOVA) and non-metric multidimensional scaling analysis (NMDS) showed that, based on both taxonomic and phylogenetic data, the community structure of AM fungi in tomato soils during the fallow period was significantly different from that of the growing period, while the difference in community composition between the flowering and fruiting stage was not significant. According to the phylogenetic structure analysis, we found that the mean net relatedness index (NRI) across all samples was equal to zero at the fallow period, indicating phylogenetic random of AM fungal community, whereas the mean NRI was significantly greater than zero in both the flowering and the fruiting stages, indicating phylogenetic clustered. These results suggest that the primary ecological process structuring communities shifted from a stochastic process at early succession to a deterministic process at the tomato growing stage when local environmental filtering increased, which inference was also supported by the neutral community model (NCM) results. Mantel test showed that soil pH, soil nutrients (SOC, total NPK, and Olsen-P) and salt content, as well as soil temperature and humidity, significantly affected the seasonal changes of AM fungal community. 【Conclusion】The highly intensive production stress in the greenhouse vegetable ecosystem promoted the transformation of the primary ecological process of AM fungal community assembly from a random process to a deterministic process, leading to a decrease in diversity and a change in community structure. Our results reveal the degradation of soil quality and the evolution of the microbiome in the process of greenhouse vegetable cultivation.

      • Effects of Plough Layer Thickness on the Transformation and Fate of Fertilizer Nitrogen in Fluvo-aquic Soils with Different Textures

        DING Shijie, YANG Wenliang, XIN Xiuli, ZHANG Xianfeng, ZHU Anning, YANG Jiao, REN Guocui, LI Mengrou

        DOI: 10.11766/trxb202204060097

        Abstract:

        【Objective】Soil fertility is significantly influenced by plough layer thickness. However, it is still not clear how the transformation and fate of fertilizer nitrogen (N) in fluvo-aquic soils would be affected by plough layer thickness. 【Method】In this study, a soil column simulation experiment in the field was conducted throughout three crop cultivations. The experiment was performed in a completely randomized design with six treatments including two plough layer thicknesses (15 and 25 cm) and three soil textures (sandy loam, sandy clay loam and loamy clay). A 15N-labeled tracer technique was used to evaluate the dynamics of fertilizer-derived organic N, fixed NH4+ and mineral N in 0~40 cm soil layer and the fate of fertilizer N in soil-crop systems. 【Result】The transformation of fertilizer N in soil-crop systems was significantly affected by plough layer thickness, and showed the same varying tendency among different textural soils. The residual fertilizer N existed mainly in the form of organic N, which accounted for more than 83% of the total residual fertilizer N and played a pivotal role in the storage and supply of fertilizer N. Increasing plough layer thickness degraded the conversion of fertilizer N to fixed NH4+ pool, while increased the stocks of fertilizer-derived organic N in 0~40 cm soil layer. In the current season after fertilizer N was applied, the average value of fertilizer-derived organic N stock in soils with 25 cm plough layer thickness (PLT-25) was averagely 8.9% higher than that in soils with 15 cm plough layer thickness (PLT-15). The stocks of fertilizer-derived mineral N under PLT-25 treatments were also higher than that under PLT-15 treatments in the current and subsequent crop cultivations; promoting the fertilizer N uptake by crops. The N use efficiency under PLT-25 treatments in the first two crop cultivations was about 8.0% higher than that of PLT-15 treatments, while the current seasonal loss rate and cumulative loss rate of fertilizer N were 12.3% and 9.1% lower, respectively. The stocks of fertilizer-derived organic N in sandy clay loam and loamy clay were significantly (P < 0.05) higher than that in sandy loam, while the trend was the opposite for the stocks of fertilizer-derived fixed NH4+. And the fertilizer-derived mineral N stock was usually to be higher in sandy loam. Overall, the percentage of recovery of applied fertilizer N in crops and soil under sandy loam treatment was significantly (P < 0.05) lower than that in sandy clay loam and loamy clay. Also, the percentage of cumulative loss of fertilizer N in sandy loam was 18.8% and 20.8% higher than that in sandy clay loam and loamy clay, respectively. 【Conclusion】The fluvo-aquic soils with higher sand content have lower fertilizer N storage capacity, restricting the enhancing of N use efficiency. For fluvo-aquic soils with different textures, increasing plough layer thickness could improve the annual N use efficiency and the residual amount of applied fertilizer N in the current season. This, could be released for crop uptake in the subsequent crop cultivation. In typical fluvo-aquic soil areas, increasing the plough layer thickness may be a potential means for regulating the transformation and fate of applied fertilizer N, increasing fertilizer N retention, enhancing the fertilizer N uptake by crops and minimizing fertilizer N loss in soil-crop systems.

      • Evolution of Iron Oxides in Aggregates of Paddy Soil Under Long-term Returning of Chinese Milk Vetch and Combined Application of Chemical Fertilizers

        HUANG Li, XIE Kun, GENG Mingjian, NIE Jun, LU Yanhong, LIAO Yulin

        DOI: 10.11766/trxb202111110611

        Abstract:

        【Objective】Iron oxides are important cementitious substances in soil aggregates, which mainly exist in soil clay particles. This study aimed to reveal the transformation of iron oxides in soil aggregates and their enrichment characteristics in clay fractions of different particle sizes under the conditions of returning Chinese milk vetch to the field and applying chemical fertilizers.【Method】Four treatments including a single application of Chinese milk vetch (MV), a single application of chemical fertilizer (F100), Chinese milk vetch applied with chemical fertilizer (MV+F100) and Chinese milk vetch combined with 80% of chemical fertilizer (MV+F80) were selected. Soil aggregates (>250, 53~250 and 2~53 μm) and clay particles (<2 μm) were separated by wet sieving and centrifugation, and the content of iron oxides in soil aggregates and their clay particles with different treatments was determined. Also, the relationship between iron oxides and the stability of aggregates was analyzed.【Result】(1) Compared with MV and F100, the content of >250 μm aggregate was increased and the content of 53-250 μm aggregate was decreased, and the mean weight diameter (MWD) and geometric mean diameter (GMD) were increased by 8.2% to 20.5% and 4.1% to 8.5%, respectively. (2) Compared with MV, the combined application of Chinese milk vetch and chemical fertilizer significantly increased the contents of amorphous iron (12.7%-55.6%, 52.4%-54.9% and 45.9%-48.6%) in aggregates of various sizes, clay particles of 2~53 μm and free clay particles. The enrichment rates of amorphous iron in >250 and 53~250 μm aggregates were decreased (32.8%~36.8% and 17.2%~28.4%). Compared with F100, the content and enrichment rate of amorphous iron in 2~53 μm aggregates and clay of aggregates were significantly reduced (3.5%~21.3%, 29.2%~30.4% and 10.9%~26.9%). (3) The content of >250 μm aggregates was positively correlated with the content of non-crystalline iron and activation degree of iron in the clay of aggregates, and positively correlated with the enrichment rate of amorphous iron and the content of free iron in aggregates. The MWD and GMD were significantly positively correlated with the content of >250μm aggregates, and significantly negatively correlated with the content of <2μm aggregate. The free iron in the clay of >250 and 2~53μm aggregates and free clays was the most important factor influencing the MWD and GMD.【Conclusion】Combined application of Chinese milk vetch with chemical fertilizer could increase the content of iron oxide in the clay of different aggregates and promote the formation of >250μm aggregates, thus, enhancing the stability of aggregates.

      • Isotopic Characteristics of Soil Water From Deep Vadose Zone of Different Typical Land Use Patterns in the North China Plain

        JIANG Pengju, WU Huawu, MIN Leilei, ZHANG Zhihua, SHEN Yanjun, Bi Huitao

        DOI: 10.11766/trxb202110180561

        Abstract:

        【Objective】The mechanisms of evaporation and infiltration during the processes of precipitation on soil layers is still not clear. Thus, this study was designed to investigate the spatial variations of soil water isotopes from deep vadose zones (>18 m) of pear orchard and farmland plots in the North China Plain. 【Method】Stable isotopes (δD and δ18O) in soil water, soil water content and soil texture were explored in the pear orchard and farmland plots of the North China Plain. 【Result】Results showed that the local meteoric water line (LMWL) was established as δD = 6.07δ18O-5.76 (R2=0.86). The δD and δ18O of soil water from different soil layers fell below the LMWL, indicating that soil water replenished from precipitation experienced strong evaporation. Except for pear orchard (I), the coefficient of variation (CV) of soil water isotopic values was in the order of shallow layer>middle layer> deep layer, indicating that the δD and δ18O of shallow soil water fluctuated greatly. This implies that shallow soil water was more impacted by precipitation and evaporation compared with other soil layers. As the profile depth increased, the effect of precipitation and evaporation gradually became weaker. The larger isotopic CV of deep soil water in pear orchard (I) indicated deep soil water was affected by groundwater at this sampling site. The d-excess values of shallow soil water were greater in pear orchard plots than those in farmland plots, indicating that the evaporation intensity of shallow soil layers was less in the pear orchard plots than in farmland plots. The obvious isotopic enrichment (δD and δ18O) was observed in the soil layer of 0.25~0.5 m, which was associated with soil texture stratification and hindered infiltration into deep soil layers. This resulted in enriched soil water accumulating in the soil layer. The phenomenon of isotopic depletion was found in the soil layers (2~5 m) from the pear orchard plots and resulted from preferential flow induced by pear roots. 【Conclusion】The remarkable spatial differences of isotopic variations in soil layers were observed in the pear orchard and farmland plots, indicating that the infiltration processes of soil water differed in various land-use patterns of the North China Plain. The preferential flow of soil water during the infiltration processes was dominated in the pear orchard plots. These findings provide a theoretical basis for understanding the relationship between water movement, nitrogen migration and transformation, and groundwater quality in the deep vadose zone of the North China Plain.

      • Study on Particle Distribution Characteristics of Soil Physical Crust Profile in Sloping Farmland

        CHEN Lin, WANG Jian, HUO Chunping, YANG Chang

        DOI: 10.11766/trxb202109110492

        Abstract:

        【Objective】 The response of runoff and erosion to soil physical crust has been extensively investigated in recent decades. However, there have been few attempts to quantify the effects of the profile of soil physical crusts on erosion processes. Thus, to explore the formation mechanism of soil physical crust in microtopography, artificial simulated rainfall and stratified soil treatment method were adopted to study the distribution and characteristics of soil particle size. 【Method】Soil plot (2.0 m long × 1.0 m wide × 0.5 m high) was set to a slope of 5°, filled with soil by contour tillage (20 cm ridges and 30 cm ditches). Simulated rainfall was designed for eight durations (5, 10, 12, 14, 16, 18, 20 and 30 minutes) and one intensity (100 mm h-1). The samples were taken out by a cutting ring (diameter 10 cm) and placed in a stratified sampling device. The bottom of the device was designed with a spiral rising bottom bracket. By turning the nut, the soil sample rises by 1 mm after turning one circle at a time with the bottom bracket. Each tier of soil sample is stripped with a soil sampling knife. Particles of samples in each tier of soil""s physical crust and the collected mud were analyzed by Mastersizer 2000. 【Result】The results showed that: (1) During erosion, the surface sand particles of structural crust (Cst), silt-containing sedimentary crust (Cscs) and silt-free sedimentary crust (Csfs) were dispersed, while the clay and silt particles were enriched, and the degree gradually increased with the duration of rainfall. (2) When the rainfall lasted for 30 min, from top to bottom of the profile, the content of sand and clay in Cst decreased by 4.61% and 1.73%, respectively, the content of silt increased by 1.83%. The content of sand and silt in Cscs and Csfs increased by 29.35% and 36.59%, 4.34% and 0.39%, respectively. The content of clay decreased by 16.30% and 14.34%, respectively. (3) In the process of crust formation, the dominant factor of Cst was raindrop dispersion, the dominant factor of Cscs and Csfs was raindrop dispersion in the early rainfall period, and sediment deposition in the late rainfall period. 【Conclusion】 Spatial location and rainfall factors are the important factors that lead to the difference in physical crust types and particle composition.

      • Spatial Variation and Influencing Factors of Soil Limiting Water Content of Granite Collapsing Gullies in Southeast Guangxi

        WEI Jiangxing, DENG Yusong, LIAO Dalan, HUANG Wanxia, HUANG Juan, JIANG Daihua

        DOI: 10.11766/trxb202107120359

        Abstract:

        【Objective】Collapsing gully is an erosion phenomenon of hillside soil under the effect of gravity damage collapse and hydraulic scouring. It is also the most serious and harmful typical soil erosion mode in the granite red soil area in South China. Collapsing gully is mainly distributed in granite hilly areas in seven provinces of Guangdong, Jiangxi, Guangxi, Fujian, Hunan, Hubei and Anhui, and their erosion modulus is large and widely distributed. This causes serious concerns for the local ecological environment and economic development. Limiting water content is an important parameter of soil hydraulic properties, which can characterize the ability of the soil state to change with a change in water content. Given that this is closely related to the stability of collapsing gullies soil, it is of great significance to predict the relationship between rainfall and collapsing gullies erosion.【Method】We selected three types of granite collapsing gullies in southeastern Guangxi, active, semi-stable and stable, as the object of study to analyze the spatial variation of soil limiting water content in each collapsing gullies and to reveal the influencing factors by using the method of path analysis.【Result】The main results were as follows: (1) Soil limiting water content of each part of collapsing gully varies spatially, the liquid plastic limit of active and semi-stable collapsing gullies soils had maximum value at top of collapsing wall (the liquid limit was 54.45% and 57.08%, the plastic limit was 32.84% and 34.04%, respectively ) and minimum value at the top of the pluvial cone (the liquid limit was 35.39% and 30.72%, the plastic limit was 21.92% and 20.23% respectively ). Also, the liquid plastic limit of stable collapsing gully had the lowest value at the bottom of the colluvial deposit (the liquid limit was 33.78% and the plastic limit was 22.47%). After gradually stabilizing the development of collapsing gullies, the limiting water content of the soil in each part showed an overall increasing trend. (2) Correlation analysis showed that clay content, organic matter, total porosity and capillary porosity were positively correlated with soil liquid plastic limit and plasticity index, with total porosity having the most significant effect on soil liquid plastic limit. Nevertheless, soil bulk, gravel content and sand content were negatively correlated with soil liquid plastic limit and plasticity index. (3) Path analysis showed that total porosity, clay content, organic matter and capillary porosity played a dominant role in the variation of the limiting water content. Furthermore, total porosity, clay content and capillary porosity were the main factors influencing the liquid plastic limit, plasticity index and liquidity index of soil, respectively. The higher the clay content, total porosity and organic matter, the higher the liquid plastic limit and plasticity index of soil. Also, the stronger the cohesion of the soil, the better the water retention performance of the soil, and the more difficult it is for the soil to crumble and be lost. Capillary porosity negatively affects the liquidity index, that is, the larger the capillary porosity, the lower the liquidity index and the more stable the soil is.【Conclusion】The limiting water content is closely related to the start-up and stability of collapsing gullies. When the limiting water content is low and is washed by rain, the soil state is easy to change, and surface runoff is produced, which causes soil collapse and fertility loss. Therefore, the results of this study can help to clarify the soil erosion process, further clarify the erosion hazards of collapsing gullies and identify high erosion risk areas. It can also provide theoretical support for the prevention and management of collapsing gullies hazard and have important significance for the prediction of regional soil and water conservation.

      • Elevational Distribution Pattern of Fungal Diversity and The Driving Mechanisms at Different Soil Depths in Mount Segrila

        SUN Yuanyuan, XU Meng, LI Yuefen, ZHANG Xubo

        DOI: 10.11766/trxb202109230511

        Abstract:

        【Objective】Unveiling the formation and maintenance mechanisms of fungal biodiversity is crucial to understand the biogeographic distribution pattern of soil fungi. However, knowledge of the elevational distribution pattern and its underlying mechanism of fungal communities in the deep layers of soil profile remains inadequate. 【Method】In the present study, topsoil (0~20 cm) and subsoil (40~60 cm) samples were collected along an elevational gradient of 3 300~4 600 m from Mount Segrila, Tibet. The variations in fungal diversity and community composition with elevation in the topsoil and subsoil and the driving factors were investigated by Illumina MiSeq high-throughput pyrosequencing of the ITS rDNA. Changes in the coexistence characteristics of soil fungal communities among different elevations and between top-and subsoil were further explored based on the calculation of niche properties. 【Result】We found that fungal communities collected from the topsoil and subsoil of Mount Segrila were dominated by Ascomycota (averaged relative abundance of 35%), Basidiomycota (46%) and Zygomycota (13%). Symbiotrophic fungi (62%) and saprotrophic fungi (33%) were identified as the major functional guilds by FUNGuild. In the topsoil, indices of fungal α-diversity (richness and Shannon diversity) decreased significantly with increasing elevation. In the subsoil, fungal richness decreased whereas Shannon diversity presented a hump-shaped pattern with increasing elevation. The dissimilarities in fungal community composition (β-diversity) increased significantly with increasing elevational distance in both topsoil and subsoil, suggesting a distance-decay pattern. The β-diversity of the fungal community was also positively correlated with environmental factors such as mean annual temperature (MAT), soil pH, the ratio of soil carbon to nitrogen, and soil moisture as suggested by the Mantel test. Results from distance-based redundancy analysis (db-RDA) suggested that pH was the driving factor for the variation in fungal community composition with elevation in the topsoil, whereas in the subsoil soil moisture was the most contributive factor. The community-level habitat niche breadth (Bcom) of soil fungi was significantly higher at 3 500 m and 3 689 m, indicating an increase in environmental fitness and a more metabolically flexible fungal community at lower elevations. However, the niche breadth of soil fungi became narrow at 4 420 m and 4 590 m, implying that soil fungi at higher elevations could be more vulnerable in response to climate change in the future. A greater degree of niche overlap (Oik > 8) between major fungal taxa was observed at lower elevations (3 356~3 689 m) and in the topsoil, whereas a lower degree of niche overlap (Oik ≤ 6) was observed at higher elevations (4 284~4 590 m) and in the subsoil. In addition, a greater degree of niche overlap was observed between Ascomycota, Basidiomycota and Zygomycota, suggesting fierce competition for resources or habitats among these taxa. The degree of niche overlap was lower between Glomeromycota, Chytridimycota and other taxa due to their symbiotic or parasitic relationships with plants. 【Conclusion】Overall, our study shows that the elevational distribution pattern of fungal biodiversity is distinctive between topsoil and subsoil, which is strongly related to the effect of environmental filtering and coexistence characteristics of specific taxa. These results may thus provide novel insights into the diversity and coexistence mechanisms of soil fungal communities in the alpine ecosystems of the Tibetan Plateau.

      • Application Zoning of Magnesium Fertilizer in Bijie Tobacco Growing Area Based on Soil Calcium-Magnesium Ratio

        ZHANG Zhongqi, ZHU Liang, WANG Meiyan, SHI Xuezheng, SUN Weixia

        DOI: 10.11766/trxb202201100014

        Abstract:

        【Objective】A reasonable supply of magnesium is an important guarantee for high-quality tobacco production. The current soil magnesium fertilizer application in tobacco growing areas is mainly determined according to the level of soil available magnesium content and its spatial distribution. However, the practical impact of the ratio of soil available calcium content to available magnesium content (Ca/Mg ratio) on magnesium supply is rarely considered. 【Method】Taking Bijie tobacco growing area as an example, the level of available magnesium content, Ca/Mg ratio and spatial distribution contours were obtained based on a large number of soil samples. Then, the suitable grade zoning of magnesium fertilizer was delimited through graphic superposition and grid operation. 【Result】The results showed that the average content of soil available magnesium in Bijie tobacco growing area was 278.1 mg· kg-1. The content shows great fluctuation in space, which was caused by the parent rock, soil type, elevation and topographic location. Also, the average Ca/Mg ratio in this area was 14.5, and was at a high level. Moreover, the spatial fluctuation of the ratio was also large, and mainly related to the spatial distribution of soil-forming parent rock and soil types. From spatial interpolation contours of available magnesium content, the areas with high content were mainly concentrated in the east and southwest, while areas with low content were mainly distributed in the middle north and northwest. The available magnesium content was dominated by the suitable grade, which accounted for 69% of the whole area. Moreover, the area of lacking and rich grades accounted for 19.0% and 10.5% respectively, and the areas of extremely lacking and extremely rich grades were both small. From the distribution of soil Ca/Mg ratio, the study area was dominated by two grades of 10~20 and 5~10, while areas covering > 20 and < 5 were relatively small. On the whole, the Ca/Mg grades were characterized by interphase distribution in space. In the application grade map of soil magnesium fertilizer obtained from available magnesium content and Ca/Mg ratio, the most suitable application areas were mainly concentrated in the north-central, southeast and northwest regions. Also, the unsuitable grades were mainly distributed in some parts of the southwest and northeast, while the areas of extremely unsuitable grade were very small, and mainly scattered in the southwest. Among all the grades, the areas of suitable and more suitable grades of magnesium fertilizer application accounted for 69.0% and 10.5% respectively. The unsuitable application area accounts for 19.0%, while the proportion of extremely suitable and extremely unsuitable areas account for only 1.3% and 0.2% respectively. 【Conclusion】The results indicate that the Ca/Mg ratio of soil is an important factor to be considered when formulating the application scheme of magnesium fertilizer. If the influence of the Ca/Mg ratio on soil magnesium supply is not considered, the appropriate grade zoning of magnesium fertilizer will have a large deviation, which will have an adverse effect on soil fertilization in tobacco growing areas. It can be seen that comprehensive consideration of soil available magnesium content and Ca/Mg ratio is an important prerequisite for scientifically formulating regional magnesium fertilizer application scheme.

      • Characteristics of Fertilizer Inputs and Soil Nutrient Accumulation in Yangshan Juicy Peach Orchard with Different Cultivation Years

        YANG Guang, WANG Yu, WANG Shenqiang, ZHAO Xu

        DOI: 10.11766/trxb202204060091

        Abstract:

        【Objective】The objective of this study was to clarify the status of soil nutrient accumulation in the peach orchard of Taihu Watershed. It aimed to provide a guide for the green production mode of peach orchard. 【Method】In this study, a total of 66 soil samples were collected from 33 juicy peach orchards, with different cultivation years in the four main planting towns. Combined with field research and laboratory analysis, the fertilizer input status, soil nutrient content and ecological stoichiometry characteristics were analyzed. 【Result】The results showed that the average total nutrient inputs was N 527 kg?hm-2, P2O5 362 kg?hm-2 and K2O 545 kg?hm-2, and the proportion of organic inputs were 27.8%, 15.4% and 15.6% respectively. Here chemical fertilizer was mainly NPK compound fertilizer, while the types of organic fertilizer applied mainly included rapeseed cake, livestock manure, and composting straw. Over-application of fertilizer could aggravate soil acidification and nutrient accumulation, soil pH in 0-20 cm and 20-40 cm soil layers of planted >10 years peach orchard both decreased by more than 1.5 units, which belonged to strongly acidic soil (4.510 years peach orchard reached level 1. The soil NO3--N concentration of the peach orchard was up to 19.3-33.1 mg?kg-1. The annual apparent surplus of N, P2O5, K2O were 343 kg?hm-2, 238 kg?hm-2 and 240 kg?hm-1, respectively. 【Conclusion】The excessive nutrient input in the peach orchard has aggravated soil acidification and nutrient accumulation. A high concentration of nitrogen and phosphorus accumulated in the soil might increase the environmental loss risk. Therefore, it is necessary to put forward a green production model for the peach production.

      • Input-Output Balance-Based P Fertilization Approach for Achieving Target Crop Yield and High P Use Efficiency: A Case Study of Cotton (Gossypium hirsutum L.) with Mulched Fertigation

        PENG Yi, YANG Guojiang, GUO Xiuli, WANG Xiaofeng, EREL Ran, FENG Gu

        DOI: 10.11766/trxb202202030044

        Abstract:

        【Objective】Maintaining moderate soil phosphorus (P) supply intensity and determining the P application rate based on the P requirement of the crop target yield, and combining with acid, slow-release water-soluble P fertilizers and applied in the early stages of crop growth is a novel P management approach in cotton. Here we test the feasibility and effectiveness of this method and provide a basis for reducing the P fertilizer application amount and increasing its use efficiency. 【Method】A two-year field experiment was employed using cotton (Gossypium hirsutum) in the moderate Olsen-P soil (23.6 mg?kg-1) in Shihezi, Xinjiang. Based on the P requirement of the target lint yield of 2.7 t?hm-2, 52.4 kg?hm-2 was selected as the P application rate. Four treatments were set-up with three types P fertilizers: (1) no P fertilizer (CK); (2) monoammonium phosphate (MAP); (3) urea phosphate (UP); and (4) ammonium polyphosphate (APP). It was analyzed that the lint yield, P uptake and above-ground biomass of cotton in different treatments. The partial productivity of P fertilizer (PFP), agronomic efficiency (AEP), P utilization efficiency (PUE) and P recovery index (the ratio of shoot P uptake to the amount of P fertilizer application, PRI) were calculated. Through stratified sampling, soil Olsen-P and P fractions in different soil layers were tested. Those allowed us to clarify the relationships between the P spatial availability and cotton growth requirements with different P fertilizers. 【Result】The significant results were: (1) The average lint yield of P applied treatments in two years was 2.73 t?hm-2, which was classified as the high yield level in northern Xinjiang. Compared with the CK treatment, the lint yield of MAP, UP, and APP treatments were increased by 21%, 25%, and 11%, respectively. (2) The P surplus was 2.2-4.8 kg?hm-2 and the P use efficiency was 24% across P applied treatments. The P recovery index of MAP, UP, and APP treatments was 91.7%, 95.6%, and 94.8%, respectively. (3) P fertilizer applied by drip irrigation in the cotton bud and boll stages can move to the 10-20 cm soil layer, which may maintain the soil P supply intensity during the cotton-growing period. Compared with the CK treatment, the mean Olsen-P in P applied treatments were increased by 94%~302%, 104%~144%, and 42%~67% in the 0~5 cm, 5~10 cm, and 10~20 cm soil layers, respectively. 【Conclusion】In summary, our results indicate that maintaining soil available P near the agronomic thresholds and determining the P application rate according to the P requirement of the target yield, and combining with acid, slow-release P fertilizer and applied in the cotton bud and boll stages can improve lint yield and P use efficacy under balanced P input-output conditions. Furthermore, the P recovery index based on the balanced P input-output can better reflect the real P use efficiency.

      • Quantitatively Partitioning Organic Carbon Loss by Interrill and Rill Erosion on The Loess Slope

        ZHANG Fengbao, LI Xuantian, SHEN Nan, YANG Mingyi

        DOI: 10.11766/trxb202201290040

        Abstract:

        【Objective】The differences in soil detachment and transport mechanisms between interrill and rill erosion lead to the differences in organic carbon loss by interrill and rill erosion. However, few studies were conducted to explore the effects and contributions of interrill and rill erosion on organic carbon loss during the erosion process because of the limitation of research methods. Successful use of the radionuclide 7Be to document soil erosion provides a means of addressing this need. The objectives of this study were to first estimate the contribution of interrill and rill erosion to sediment yield and then quantitatively explore the effects and contributions of interrill and rill erosion on organic carbon loss on the loess slope. 【Method】The simulated rainfall experiments with five slope gradients (5°, 10°, 15°, 20°, 25°and 30°) were conducted under different rainfall intensities in the field to investigate soil and organic carbon loss and 7Be tracing technology was used to quantify the contribution rate of interrill and rill erosion on sediment yield and organic carbon loss for the loess slope.【Result】Interrill erosion is the main and the relative contribution of interrill erosion on sediment yield was 86% on the 5°plot. But rill erosion dominated on the plots with gradient greater than 5°. The relative contribution of rill erosion on sediment yield ranged from 61% to 71% and could even reach 96% during the rainfall. The average enrichment ratio of organic carbon of sediment from the entire plot and the interrill area was 1.16±0.15 and 1.50±0.50, respectively, during the rainfall. The enrichment could increase organic carbon loss rate of 0.008 to 0.028 g m-2 min-1. The relative contribution of rill erosion to organic carbon loss were between 55% and 62% on plots with gradient greater than 5°, which were lower than those of rill erosion to sediment production, but still dominated. Sediment yield from the entire plot and the interrill area could respectively explain 97% and 89% of the variations of organic carbon loss from the entire plot and the interrill area. 【Conclusion】The organic carbon enrichment ratio had less effects on organic carbon loss when rill erosion occurred severely. Sediment yield determined the amount of organic carbon loss. Severe rill erosion could enhance the enrichment ratio of organic carbon of sediment from the interrill area.

      • Proteomic Dissection of the Rice Shoots in Response to Iron Deficiency and Excess

        ZHANG Xin, WANG Ruonan, SHEN Renfang, LAN Ping

        DOI: 10.11766/trxb202203150109

        Abstract:

        【Objective】In calcareous soils, iron (Fe) generally exists in the form of oxides or hydroxides, which is not conducive to plant absorption and utilization, thus frequently causing Fe deficiency in plants. In flooded acidic soils, such as paddy soil, due to conditions of irrigation and drainage and alternate cultivation of water and drought, the redox potential of the soil is low and ferric Fe is reduced to be ferrous. The ferrous Fe is readily absorbed and utilized, resulting in excessive Fe absorption by plants. Fe deficiency and excess are limiting factors affecting rice yield and quality. Fe deficiency leads to chlorosis and reduces plant growth while Fe overload is toxic for plants, with a typical symptom of leaf bronzing. Several transcriptome analyses have been performed to investigate the responses under Fe stress. However, a comprehensive dissection of the entire Fe-responsive profile at the protein level is still lacking. It is necessary to analyze the rice responses under Fe deficiency and Fe excess using proteomic analysis. 【Method】In this study, a label-free proteomic analysis was performed on rice shoots grown in Fe-deficient (0 μmol?L-1), Fe-sufficient (40 μmol?L-1), and Fe-excess (350 and 500 μmol?L-1) conditions. 【Result】Results showed that 130, 157 and 118 differentially accumulated proteins (DAPs) were identified under Fe deficiency and two concentrations of Fe excess stresses, respectively, compared with Fe sufficient conditions. Gene ontology enrichment analysis of the DAPs revealed that primary metabolic process, organonitrogen compound metabolic process, response to stimulus, and oxidative stress responses were significantly enriched under both Fe deficiency and excess stresses. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that DAPs under Fe deficiency and Fe excess were commonly enriched in metabolic processes like the ribosome, photosynthesis, and oxidative phosphorylation. Notably, the abundance of proteins involved in phenylpropanoid biosynthesis and biosynthesis of cofactors was mainly affected by Fe deficiency, while the abundance of proteins involved in the biosynthesis of amino acids was mainly influenced by Fe excess. Under Fe excess stress, the abundance of enzymes involved in amino acid metabolism was decreased, indicating a reduction in the content of plant-synthesized amino acids. However, the increased abundance of transketolase involved in photosynthesis and secondary metabolism probably reduced the inhibitory effect induced by Fe stress. Ribosomal proteins S16, Os03g0798600 and RPL17 may play important roles in response to Fe deficiency and Fe excess stresses, but the exact functions of these proteins under Fe stress are still unknown. Several novel proteins which may play potential roles in rice Fe homeostasis were also predicted in this study.【Conclusion】Overall, our results indicate both Fe deficiency and Fe excess stresses affected photosynthesis and ribosomal metabolism. The synthesis of phenylpropane was mainly affected by Fe deficiency, while amino acid metabolism was mainly affected by Fe excess in the shoots of rice. The findings will provide some information for the exploration of key factors for the efficient absorption and utilization of Fe.

      • Formation and Stability Mechanism of Soil Aggregates: Progress and Prospect

        LIU Yalong, WANG Ping, WANG Jingkuan

        DOI: 10.11766/trxb202112180686

        Abstract:

        As the basic unit of soil structure, soil aggregates play an important role in the soil and are vital for maintaining soil ecological functions (such as carbon sequestration and nutrient retention, etc.). The formation and stability of aggregates are based on the complex interactions between minerals, organic matter and organisms in the soil, but the mechanisms of these interactions still lack a systematic summary. This article reviews the research history of soil aggregates over the past century and sorts out the historical nodes for the proposition of key theories, including important theoretical viewpoints, main theoretical models (Monnier’s aggregate stability model, Tisdall and Oades’ aggregate hierarchy model, Six’s aggregate turnover model and Christensen’s tertiary structure model), indexes for evaluating the structure and stability of soil aggregates, comparison of two main sieving methods (dry and wet sieving), and classification basis and classification type for soil aggregates. Furthermore, it expounds on the action mechanism of aggregate basic structural units (minerals, organic matter, organisms and their derivatives) and the formation and stabilization mechanism of microaggregates and macroaggregates, detailing the aggregate formation by organo-mineral interactions (Wershaw’s bilayer model and Kleber’s zonal model) and biological control of aggregate turnover (Miller’s sticky string sag theory). Through this review, it is found that there are more in-depth discussions on the factors affecting the formation and stability of soil aggregates, but few studies have addressed the effects of pH and redox processes on the aggregates in the paddy and waterfront soil systems. Finally, the future development of soil aggregate research is highlighted, in expectation of providing theoretical reference for the sustainable use of soil resources.

      • Effects of Vegetation Restoration on Functional Groups Related to Soil Carbon, Nitrogen and Phosphorus Cycles in Open-pit Mining Area of the Loess Plateau

        CHEN Fu, ZHAO Jiao, ZHU Yanfeng, LUO Zhanbin

        DOI: 10.11766/trxb202203170117

        Abstract:

        【Objective】The ecology of mining areas in the Loess Plateau is relatively fragile, while the vegetation restoration is closely related to soil microbe-mediated nutrient cycling. This study was designed to clarify the influence and regulatory roles of vegetation restoration on the functional groups related to soil carbon, nitrogen and phosphorus cycles, which are significantly important to rebuilding the ecological resilience and self-sustaining mechanism of mining areas.【Method】In this study, high-throughput qPCR chip technology, random forest model and structural equation model were used to reveal the changes and mutual feeding mechanism of soil characteristics, enzyme activities, carbon, nitrogen and phosphorus functional groups under different vegetation restoration modes of Antaibao open-pit reclamation waste dump on the Loess Plateau. 【Result】 The results showed that Caragana korshinskii (bushwood, BL), Pinus tabuliformis (coniferous forest, CF), Robinia pseudoacacia (broad-leaved forest, BF) and Robinia pseudoacacia + Ulmus pumila (mixed forest, MF) were superior to soil nutrient accumulation compared with Populus simonii forest (CK). Compared to CF, soil organic carbon (SOC) of BL, BF and MF increased by 82.26%, 168% and 56.65%, respectively. The total nitrogen (TN) of BL, BF and MF enhanced by 68.31%, 130% and 46.75% comparing with CF, while the available phosphorus (AP) contents increased by 10.41%, 27.65% and 20.89%, respectively. Nevertheless, these were still significantly lower than that of CK (P< 0.05). The soil catalase (CAT) activities of BL, CF, BF and MF increased by 95.6%, 101.0%, 46.4% and 120.0% respectively, and are significantly higher than that of CK (P<0.05). Also, the soil β-glucosidase (BG) and leucine aminopeptidase (LAP) activities decreased significantly (P<0.05). The β-glucosidase activities of BL, CF, BF and MF decreased by 66.5%, 67.0%, 58.9% and 59.8%, while the leucine aminopeptidase activities decreased by 57.8%, 67.7%, 78.0% and 67.7%, respectively. The different modes of vegetation restoration significantly changed the relative abundances of functional groups related to carbon, nitrogen and phosphorus (P<0.05), whereas the variation tendencies always keep a consistent correspondence. The functional groups related to carbon, nitrogen and phosphorus were significantly positively correlated with soil nitrate nitrogen (P<0.001), but they presented negative correlations with ammonium nitrogen (P<0.01). The functional groups involved in the carbon cycle, nitrification process and organic phosphorus mineralization were significantly positively correlated with available phosphorus (P<0.01). In addition, results of the structural equation model showed that vegetation restoration could directly affect CAT and AP, thereby regulating the carbon, nitrogen and phosphorus cycle. Otherwise, the vegetation restoration could affect soil AP indirectly, thereupon then regulating the abundances of carbon, nitrogen and phosphorus functional groups, together with other soil characteristics, such as nitrate nitrogen or ammonium nitrogen. 【Conclusion】 This study might help deepen the knowledge about soil microbiology mechanism of vegetation restoration, which will furtherly help the ecological restoration of damaged mines in the Loess Plateau.

      • Progress and prospect of biological salt removal from farmland under drip irrigation inarid area of northwest China

        suyuan, Tian Chang yan, Mai Wen xuan, Wanglei, Zhao Zhen yong, Zhou hong fei

        DOI: 10.11766/trxb202202150008

        Abstract:

        Since the end of the 20th century, mulched drip irrigation technology has been widely promoted and applied in arid areas of northwest China, which has greatly pushed the development of oasis agriculture. However, the salt in water brought by drip irrigation cannot be discharged from the soil, which makes the sustainable development of oasis agriculture in arid areas challenging. Therefore, preventing and controlling secondary salinization of farmland to make use of the salt and alkali land resources widely distributed in the arid area of northwest China under conditions of water resource shortage is an urgent problem to be solved in order to promote sustainable development of agriculture. This article sorted literature on biological salt removal and the aspect of salt tolerance mechanism, growth and development of halophytes to salt, mutual feedback effects between salt removal of halophytes and reclamation of saline-alkali soil, and the effects of planting halophytes on soil water and salt dynamics. Also, this study points out the existing problems in the research of biological salt removal in arid areas of the northwest and suggests prospects for further research works. The study can provide decision bases for making reasonable, efficient and comprehensive salt removal systems in arid area agriculture and is of great significance for realizing salt balance in farmland, alleviating soil secondary salinization crisis and soil sustainable utilization.

      • Effects of residence time on 13C and 15N abundances of rice and rice derived-biochars after a dual isotope labeling

        Zhang Fangchao, Lu Weiwei, Zha Quanzhi

        DOI: 10.11766/trxb202203250133

        Abstract:

        【Objective】To provide a basis for an advanced on the impacts of biochar on soil carbon and nitrogen cycling, the effects of residence time after isotope labeling on the δ13C and δ15N values of rice aboveground and underground tissues and biochars derived from these two tissues were studied. 【Method】Rice plants were labeled with 13C and 15N by pulse labeling of 13C-CO2 and foliar fertilization of 15N-urea, respectively. The residence time of 4 h, 6 h and 24 h was set after 15N isotope labeling. The labeled rice plants were divided into aboveground and underground tissues and four biochars were produced by pyrolyzing these two tissues at 300 ℃ and 500 ℃, respectively. The δ13C and δ15N values of rice tissues and their biochars were determined by isotope mass spectrometry. 【Result】With the increase in residence time, δ13C values of the aboveground tissues of rice plants gradually decreased from 872‰ to 578‰, while the δ13C values of the underground tissues gradually increased from 226‰ to 869‰. Unlike with the δ13C, the δ15N values in the aboveground tissues of rice plants first increased then decreased, and the maximum (1764‰) occurred at the residence time of 6 h, while δ15N values in the underground tissues first decreased and then increased. Overall, compared to rice tissues, the δ13C and δ15N values of the biochars decreased by 52.1% and 15.9%, respectively. Moreover, both the δ13C and δ15N values of the biochars were highest at the residence time of 24 h, especially for the 300 °C biochar. With the increase in residence time, the reduced proportion of the δ13C of hot water extractable dissolved organic carbon when compared with that of the residual solid increased from 4.14% to 11.0% for the 300 °C biochar, while it decreased from 32.3% to 18.9% for the 500 °C biochar. This indicates that increase in the residence time decreased and increased the uniformity of 13C of the 300 °C and 500 °C biochars, respectively. 【Conclusion】Our results demonstrate that the effects of residence time after labelling on δ13C and δ15N values of the rice plants were different, and the biochars did not retain the isotopic signature of the raw rice tissues. Residence time and pyrolysis temperature together affected the uniformity of 13C in rice biochars.

      • Effects of microscopic water and nutrient conditions on the host lysis process of Pseudomonas aeruginosa phage

        Wang Yan, Ruan Chujin, Xie Wenlin, Zhu Kun, Chen Guowei, Liu Ying, Wang Gang

        DOI: 10.11766/trxb202201070528

        Abstract:

        Abstract: [Objective] This study was designed to investigate the growth and migration of bacteria and phages under different water and nutrient conditions, as well as the process and mechanism of the interactions between bacteria and phages. [Methods] Using the agar plate, the interaction of Pseudomonas aeruginosa PAO1 and Pseudomonas phage PA-27-1 were performed. [Results] The coexistence of bacteria and phages is mainly affected by phase-induced lysis of bacteria, motility of bacteria and the diffusion of phages. Moisture regulated the relative water film thickness and connectivity on the porous surface of plates. It also affected the movement and proliferation of bacteria, the formation process of biofilms, and morphological characteristics of colonies on the porous interface. Additionally, it regulated the interaction mechanism between bacteria and phages by affecting the spread of phages. Different motility patterns and individual sizes between bacteria and phages also led to differences in their proliferation (diffusion) characteristics in micro-pores. Lower water film thickness and patchy distribution promoted the spatial isolation between bacteria and phages and reduced the probability of phage-reduced lysis, which was important for the proliferation of bacteria. [Conclusions] This study reveals the migration of phages and bacteria in micro-habitats like biofilm and provides a theoretical basis and data support for the temporal and spatial distribution of soil phages, as well as the interaction pattern between soil phages and soil bacteria.

      • Response of nitrite-dependent anaerobic methane oxidation in paddy fields to slow increase of atmospheric CO2 concentration

        Jin Jinghao, Huang Hechen, Shen Lidong, Tian Maohui, Liu Xin, Yang Wangting, Yang Yuling, Liu Jiaqi, Ren Bingjie, Xu JiangBing, Hu Zhenghua

        DOI: 10.11766/trxb202111250641

        Abstract:

        Nitrite-dependent anaerobic methane oxidation (n-damo) is a novel pathway for controlling methane emissions from paddy ecosystems. However, the contribution of n-damo to methane oxidation and its response to elevated atmospheric CO2 concentration are poorly known. Here, an ambient CO2 treatment (CK) and a slow increase of atmospheric CO2 treatment (EC: an increase of 40 μL·L-1 per year above CK until 160 μL·L-1) were set up based on the CO2 automatic control platform with open top chambers. The stable isotope tracer experiment, quantitative PCR and high-throughput sequencing were employed to investigate the n-damo activity, abundance, diversity and community composition of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria in paddy soils across key rice growth stages (tillering, jointing and flowering stages) under different CO2 treatments. The results showed that EC treatment stimulated the n-damo activity and abundance of M. oxyfera-like bacteria, particularly at the jointing stage. Further, EC treatment significantly changed the community composition and diversity of M. oxyfera-like bacteria. The variations in soil dissolved organic carbon content and inorganic nitrogen content under EC treatment could probably cause the change of n-damo activity and the community structure of M. oxyfera-like bacteria. Taken together, our results showed a positive response of n-damo to the slow increase of atmospheric CO2 concentration, suggesting its active role in reducing methane emissions from paddy fields under the future climate conditions.

      • Molecular Characteristics of Soil Dissolved Organic Matter in Response to Decomposition of Organic Fertilizers from Different Sources

        CHEN Liming, WU Yueying, LI Caisheng, WU Zhipeng, HUANG Cheng, JI Hengkuan, HOU Zhengwei, FU Chuanliang, ZHAO Yidong, WU Weidong

        DOI: 10.11766/trxb202111290519

        Abstract:

        【Objective】 Dissolved organic matter (DOM) derived from organic fertilizers may provide new insights into the potential applications of different commercial organic fertilizers.【Method】Herein, four different sources of organic fertilizers (biochar, WSB; sheep manure, SM; seaweed, SW; shrimp peptide, SP) with soils around the Changhua mine site were used to carry out a three-month incubation experiment. The subsequent effect of organic fertilizer amendment on molecular characteristics of soil DOM was investigated using multivariate spectral analysis. 【Result】Compared to the control, soil DOM concentrations significantly increased in response to organic fertilizers amendment during the whole incubation period, exhibiting the lowest increment in WSB treatment and the highest increment in SW treatment, respectively. The excitation-emission matrix with parallel factor (EEM-PARAFAC) showed that WSB increased the proportion of humic-like fluorophore of soil DOM while fulvic acid-like fluorophore decreased during the whole incubation period. Also, SM, SW and SP amendments lowered the proportion of microbially-transformed humic-like fluorophore and increased the proportion of fulvic-acid like fluorophore during 0-45 days, but increased the proportion of refractory humic-like fluorophore during 45-90 days. Two-dimensional correlation spectroscopy analysis on Fourier-transform infrared (2D-FTIR-COS) spectroscopy revealed that aromatic/carboxylic acid groups of soil DOM in the control and SP treatments and alkene/polysaccharide groups in the added WSB, SW and SM treatments had the fastest responses over time, respectively. In addition, Si-O-Al signals from soil nano-minerals functional groups exhibited a distinct response over time in the added WSB and SP treatments. The carbon near-edge X-ray absorption fine structure (C 1s NEXAFS) analysis showed that compared to control, the added WSB increased the proportion of oxygenated aliphatic fractions but reduced aromatic/phenolic fractions of soil DOM after incubation. Also, SW increased the proportion of aromatic and carbonyl fractions but reduced aliphatic and oxyalkyl fractions while SM and SP increased the proportion of phenolic, aromatic and aliphatic fractions but reduced the proportion of carboxyl, oxyalkyl and carbonyl fractions. 【Conclusion】The results of this study can enhance our understanding of how the decomposition of different sources of organic fertilisers affects the molecular characteristics of soil DOM. This is essential for assessing the ecological effects of the application of commercial organic fertilisers in soils.

      • Grazing Effect on Activity and Diversity of Soil Methanotrophs in Winter Pastures of the Loess Plateau

        WANG Yufang, CAI Yuanfeng, HOU Fujiang, BOWATTE Saman, JIA Zhongjun

        DOI: 10.11766/trxb202112080664

        Abstract:

        【Objective】Soil methanotrophs are the only biological sink of atmospheric methane (CH4). Grazing can regulate the methane oxidation activity of the soil by affecting the abundance and diversity of soil methanotrophs. 【Method】In this study, we collected soil samples in winter pasture from different intensities of continuous grazing on typical grasslands in the Loess Plateau and used laboratory incubation and high-throughput sequencing to determine methane oxidation activity, composition and abundance of soil methanotrophs.【Result】The results showed that the grassland was CH4 sink, and the medium grazing (MG) and high grazing (HG) intensity increased the rate of methane oxidation. Meanwhile, the mean abundance of methanotrophs in HG and MG also increased significantly compared with CK. The results of high-throughput sequencing showed that grazing had a significant impact on the diversity of methanotrophs, Upland soil cluster gamma (USCγ) was the dominant methanotrophic group under different grazing intensities, and a small amount of Methylocaldum and Methylocystis were also present. Pearson correlation analysis showed that methane oxidation rate (MOR) showed a significant positive correlation with soil moisture content and NO3--N content ( P< 0.05), and significantly positively correlated with the absolute amount of USCγ (P < 0.01), which indicated that USCγ played a major role in the process of methane uptake in this grassland.【Conclusion】This study proved that grazing can improve the methane sink function of typical grasslands in the Loess Plateau.

      • Effects of Plantation Restoration on Chemical Properties and Bacterial Community in Soil Profiles in Mu Us Sandy Land

        TIAN Jing, BU Lianyan, CHEN Wenfeng, AN Derong, ZHANG Yinglong, WEI Gehong, WANG Honglei

        DOI: 10.11766/trxb202112200405

        Abstract:

        【Objective】Afforestation is the main measure for desertification combating and plays a key role in improving soil quality and reestablishing degraded ecosystem functions. However, the spatial distribution in soil chemical properties and bacterial communities after the forest reconstruction in sandy land has not been well evaluated. The objective of this study was to investigate responses of the soil chemical properties and bacterial communities in soil profiles to afforestation and to provide a scientific basis for the healthy management and fertility cultivation of barren sandy soils in Northern China. 【Method】In this study, we selected Pinus sylvestris var. mongolica plantations which included 0, 5, 8, and 15 by using the space-time substitution method in Mu Us Sandy Land located in Yulin, Shannxi, China. Soil samples were collected from 0-10 cm, 10-20 cm, 20-30 cm, 30-60 cm, and 60-100 cm. The high-throughput amplicon sequencing of the 16S rRNA and Functional Annotation of Prokaryotic Taxa (FAPROTAX) tool was used to quantify the composition, diversity, and putative ecological functions of soil bacterial community, and then to determine the relationship between bacterial community and soil properties. 【Result】Results showed that: (1) The conversion from sandy land to plantations increased soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, but decreased available nitrogen (AN), available phosphorus (AP) contents, and pH. TN content decreased with soil layers, while AP and pH were increased. TP had no significant change in soil profiles. (2) Afforestation significantly changed the relative abundance of the Proteobacteria, Acidobacteria and Chloroflexi, and increased soil bacterial ACE (abundance-based coverage estimator) index. Importantly, the vertical spatial variation in bacterial communities decreased. (3) FAPROTAX showed that after 15 years of afforestation, cellulolysis and aromatic compound degradation decreased by 54.65% and 72.18%, respectively. However, nitrogen fixation and denitrification were enhanced by 99.26% and 100.5%, respectively. (4) Redundancy analysis and Pearson correlation analysis indicated that SOC and pH were the key factors varying the bacterial community and putative ecological functions. 【Conclusion】Overall, the conversion from sandy land to Pinus sylvestris var. mongolica plantations can negatively affect soil available nutrients such as AN and AP, and also alter the diversity and putative functions of the soil bacterial community. Consequently, artificial control measures (such as regulation of litter degradation and nutrient return) are crucial for improving the bioavailability of nutrient elements and microbial functional diversity in arid and barren sandy soil. In the future, on-the-spot preservation and decomposition of litter in the ecological restoration work of artificial forests in sandy areas should be prioritized.

      • Research Progress on In-situ Passivation Remediation Technology of Cadmium and Arsenic Compound Contaminated Paddy Soil

        CAO Rui, WANG Yue, CHEN Shuang, ZHENG Lingyun, XU Li, ZHOU Jihai, LI Huixin, HU Feng

        DOI: 10.11766/trxb202112170524

        Abstract:

        Paddy soil is suffering from serious heavy metal pollution due to rapid industrial and agricultural development. As the main food crop in South Asia and Southeast Asia, rice safety issues are particularly prominent due to increasing heavy metal pollution. The remediation of cadmium and arsenic-contaminated paddy soil has always been a complex issue because of the differences in their biogeochemical cycle. Our study reviews the research progress on in-situ passivation technology for paddy soil contaminated by cadmium and arsenic. We group the passivation technology into four types: redox type, microbial transformation and accumulation type, material immobilization type, and coupled passivation technology. Redox type passivation technology focuses on the migration and transformation mechanisms of Cd and As driven by Eh, pH changes, biogeochemical cycles of different elements, and organic matter under the influence of water regulation in paddy fields; microbial transformation and accumulation type passivation technology focuses on clarifying the mechanism of functional microorganisms on the absorption, transformation, compartmentalization and bacterial surface adsorption of arsenic and cadmium; material immobilization type passivation technology focuses on the classification of existing passivation materials and their immobilization mechanisms with cadmium and arsenic; coupled passivation technology focuses on summarizing the application analysis of synergistic passivation of cadmium and arsenic under the comprehensive system of the above three technologies. Also, we propose the forecast on the in-situ passivation restoration of paddy soils contaminated by cadmium and arsenic. Besides, the research direction of new mechanisms involved in the biogeochemical cycle of cadmium and arsenic in paddy soil, the innovation and extension trend of remediation technology are further discussed. We hope that a soil passivation improvement technology model will be created in future, which integrates modern agricultural production models with a guarantee of food production and security.

      • Data Assimilation for Soil Hydraulic Parameter Estimation: Progress and Perspectives

        MAN Jun, ZHANG Jiangjiang, ZHENG Qiang, YAO Yijun, ZENG Lingzao

        DOI: 10.11766/trxb202203040090

        Abstract:

        The characterization of soil hydraulic parameters and their heterogeneity is related to many scientific problems in soil and groundwater fields. Due to the limitation of time and sampling cost, the traditional experimental approaches cannot address this issue adequately. With the development of Internet of Things technology, the state variables related to soil water movement (such as water content and pressure head) can be acquired in real time through sensors. This has sparked some debates about how to estimate the soil hydraulic parameters using these measurements. Data assimilation methods can estimate the soil hydraulic parameters by integrating the measurements into numerical models. This paper systematically analyzes the uncertainty sources and measurement approaches of soil hydraulic parameters, expounds on the basic principles of several common data assimilation methods and their applications in soil hydraulic parameter inversion, and discusses the latest advances in data assimilation methods from aspects of computational efficiency and accuracy. Finally, the development direction of data assimilation methods is provided. The results show that the data assimilation methods can break through the limitation of the traditional experimental approach, and thus are suitable for the characterization of soil hydraulic parameters and their heterogeneity. However, limitations such as the strong nonlinearity of the unsaturated flow model, spatial heterogeneity of soil and sparsity of in-situ measurements do exist. It is, therefore, essential for us to unfold in-depth research on soil hydraulic parameter inversion from the aspects of supervised dimension reduction method, multi-source and multi-scale data fusion, and coupling of machine learning with physical laws, thereby assisting agricultural soil and water management as well as the prevention, control, and remediation of pollution in agroecosystems.

      • Effect of Tillage Practices on Soil Pore Structure Characteristics in Shajiang Black Soil

        QIAN Yongqi, XIONG Peng, WANG Yuekai, ZHANG Zhongbin, GUO Zichun, SHAO Fangrong, PENG Xinhua

        DOI: 10.11766/trxb202201190027

        Abstract:

        【Objective】Shajiang black soil is one of the major soil types with low or medium productivity in China and is mainly distributed in the Huai River North Plain. As the soil is high in clay content and its parent material is dominated by montmorillonite, it suffers from swelling/shrinkage, low infiltration and strong strength. Suitable tillage is widely considered an effective measure to improve soil structure. However, how tillage practice impacts the pore structure of Shajiang black soil is not clear. Therefore, the objective of this study was to assess the effect of different tillage practices on soil pore structure characteristics in Shajiang black soil. 【Method】Intact soil columns (20 cm height, 10 cm diameter) were sampled from three tillage treatments including no-tillage (NT), rotary tillage (RT) and deep ploughing (DP) at Longkang Farm in Anhui Province, and then were scanned using X-ray computed tomography at a voxel resolution of 60 μm, and followed by saturated hydraulic conductivity (Ks) measurement. After reconstruction of CT images, characteristics of soil macropore (>60 μm) morphology and networks were quantified with Image analysis. 【Result】Compared to no-tillage, rotary tillage and deep ploughing increased soil macroporosity by 192.7% and 261.1% (P < 0.05), respectively. Rotary tillage and deep ploughing significantly increased the hydraulic radius, compactness, fractal dimension and global connectivity of soil macropores (P < 0.05), but decreased the degree of anisotropy and Euler number (P < 0.05). The Ks was significantly improved under rotary tillage and deep ploughing. Deep ploughing improved soil structure and Ks better than rotary tillage did. A significant correlation was observed between Ks and macropore structure characteristic parameters (P < 0.05), in which the connected largest macroporosity was the highest (r=0.833**, P < 0.01). 【Conclusion】Deep ploughing enhanced pore hydraulic radius, connectivity and complexity, built a good soil pore morphology and network structure and consequently improved hydraulic conductivity and reduced structural obstacles of Shajiang black soil.

      • Effects of Typical Components of Root Exudates on the Stability and Transport of Biochar Colloids

        PAN Yue, ZHANG Yu, WANG Yang, SHANG Jianying

        DOI: 10.11766/trxb202107110358

        Abstract:

        【Objective】Root exudates are the main sources of dissolved organic matter, which can affect the stability and transport behaviors of colloids in porous media to some extent. With the wide application of biochar in soils, it is very important to understand the effects of root exudates on the stability and mobility of biochar colloids in the subsurface environment. 【Method】Galactose (Gal), lysine (Lys) and acetic acid (AcOH) are the typical components of root exudates. This study investigated the effects of Gal, Lys and AcOH on the stability and transport behaviors of wheat biochar (WB) and pine sawdust biochar (PB) colloids by aggregation and transport experiments. 【Result】The results showed that the concentration of root exudates had a certain influence on the ζ potential of biochar particles. At low Gal and Lys concentrations, their effects on the aggregation and transport of biochar colloids were small, thus, there were no significant effects on the environmental behavior of biochar colloids. In contrast, AcOH reduced the stability of biochar colloids in NaCl solution and inhibited the transport of biochar colloids in porous media. This may be related to the fact that the organic acid anions in acetic acid were easy to form hydrogen bonds with the oxygen-containing functional groups on the surface of biochar. Thus, the adsorption of AcOH by biochar was increased and the stability of biochar colloids was decreased. 【Conclusion】The concentration of root exudates such as Gal and Lys plays an important role in their ability to influence the aggregation and transport of biochar colloids. However, the adsorption of AcOH, even at low concentrations, significantly affects the aggregation and transport of biochar colloids.

      • Distribution and Stabilization of Photosynthetic Carbon in Rice-soil System Under Long-term Multiple Cropping of Green Manure

        LIU Weimin, SHU Yeqin, XIA Yinhang, XIANG Hongkun, GAO Peng, ZHAO Ziwei, HUANG Jing, GAO Jusheng, ZHANG Zhenhua

        DOI: 10.11766/trxb202112060640

        Abstract:

        【Objective】Winter multiple cropping of green manures such as Chinese milk vetch and rapeseed is a traditional system for improving soil fertility and crop yield in the rice field in southern China. Thus, it is of great importance to analyze the soil carbon (C) cycle and the ecological functions of green manure by exploring the distribution of photosynthetic C in a rice-soil system under long-term winter cropping of green manure. 【Method】In this study, based on a 38-year rice-rice-green manure cropping experiment, the 13C-CO2 pulsing labeling technology was used to study the distribution characteristics of photosynthetic C in a rice-soil system at the tillering stage of early rice season under long-term green manure (Chinese milk vetch, rapeseed and winter fallow). At the same time, the stability of 13C-photosynthetic C in soil was studied by measuring the content and distribution ratio of 13C in particulate organic carbon (POC) and mineral associated-organic carbon (MAOC). 【Result】The results showed that the biomass of rice at the tillering stage was not significantly changed but the root/shoot ratio was decreased by 12.6%-19.4% with the long-term multiple cropping of green manure. Compared with winter fallow treatment, the cropping of green manure promoted the distribution of 13C-photosynthetic C in the shoot of early rice, and the accumulation of 13C-photosynthetic C was increased by 19.9 mg?plant-1 and 80.6 mg?plant-1 in cropping of Chinese milk vetch and rapeseed treatments, respectively. The 13C-photosynthetic C accumulation in the root of early rice was decreased by 2.7 mg?plant-1 under Chinese milk vetch treatment, while it was not significantly affected by rapeseed treatment. This result infers that long-term multiple cropping of green manure increased soil nutrient supply and reduced the ratio of root to shoot of early rice, which allows the rice to distribute more biomass to the shoot. Meanwhile, the cropping of Chinese milk vetch and rapeseed treatments reduced the distribution of 13C-photosynthetic C in the soil by 7.6 mg?plant-1 and 7.8 mg?plant-1 respectively. The proportions of rice 13C-photosynthetic C to POC and MAOC were not significantly affected by the cropping of Chinese milk vetch, but the proportion of 13C-photosynthetic C in POC was increased by 35.3% with multiple cropping of rapeseed. 【Conclusion】The long-term multiple cropping of green manure promoted the accumulation of rice photosynthetic C in the plant-soil system. Compared with winter fallow treatment, the accumulation of photosynthetic C in the rice-soil system increased by 3.7%-28.0% in cropping of Chinese milk vetch and rapeseed treatments. On the other hand, the long-term multiple cropping of green manure increased the distribution of photosynthetic C to the shoot of rice and reduced the proportion of photosynthetic C to the root of rice and soil. Moreover, the stability of rice photosynthetic C in soil was weakened by multiple cropping of rapeseed treatments. From the perspective of increasing the total organic carbon and the stability of photosynthetic carbon, the cropping of Chinese milk vetch treatment is a better system for winter multiple cropping of green manures.

      • Medicinal Liquid Diffusion and Weed Control Effect Based on Drip Irrigation System under Maize Film

        GUO Zhijie, ZHANG Haiying, LI Jianjun, XU Shengjun, JING Zhuoqiong, LÜ Heping

        DOI: 10.11766/trxb202112270633

        Abstract:

        【Objective】This study aimed to explore the possibility of herbicide application in a drip irrigation system. To do this, the relationship between the application technology of soil closed herbicide and the control effect of weeds in the field were studied by using a drip irrigation system under film.【Method】Under three different drip irrigation belt spacing, 40% ethyl atrazine emulsion was applied in three ways. After the drip application, the herbicide concentration in soil samples in different distribution areas was evaluated. In order to provide a scientific basis for rational application of drip irrigation weed control technology in a maize field and enrich drip irrigation application theory, the control effect was investigated in the stage of weed occurrence. 【Result】The results showed that the distribution of herbicide in soil after it was applied was not related to the laying distance of drip irrigation belt, but was related to washing time of water after the last application. The longer the washing time, the lower the concentration of acetochlor in soil, the obvious vertical settlement, and the shorter the radial diffusion distance. Through drip application, the control effect of weed plant and fresh weight was the best after 15 min of drip irrigation, 30 min of drip irrigation and 5 min of drip irrigation. 【Conclusion】It is feasible to apply soil sealing herbicide with drip irrigation in a mulched maize field, which can save time, labor and energy, and provide a new method for early weed control in a maize field. Nevertheless, it is necessary to carry out practical technology optimization research according to different pesticide types and properties.

      • Effects and Mechanisms of Different Kinds of Catch Crops on Reducing Nitrogen and Phosphorus Leaching Loss in Protected Vegetable Field

        JU Shengrong, MIN Ju, DONG Gangqiang, LI Jianbin, SHI Weiming

        DOI: 10.11766/trxb202112010590

        Abstract:

        【Objective】Planting catch crops in a protected vegetable field during the fallow season is an important practice to reduce the leaching loss of important nutrients. However, few studies have been done on catch crops with high nitrogen and phosphorus leaching control efficiency in frequent rainfall areas.【Method】This research set up five planting catch crop treatments (sorghum treatment, maize treatment, ryegrass treatment, purslane treatment and collard treatment) and a fallow treatment to study the effect of different kinds of catch crops on nitrogen and phosphorus leaching, NO3--N and NH4+-N content and soil microorganism.【Result】The results showed that compared with fallow treatment, sorghum, maize, ryegrass, purslane and collard treatments significantly reduced nitrogen leaching by 12.6, 26.6, 27.4, 28.9 and 26.8 kg?hm-2 and phosphorus by 0.10, 0.05, 0.04, 0.04 and 0.13 kg?hm-2, respectively. The nitrogen and phosphorus control efficiency was as follows: purslane>ryegrass>collard>maize>sorghum, and collard>sorghum>maize>purslane>ryegrass, respectively. The nitrogen control rates of ryegrass, purslane and collard reached 52.3%, 55.1% and 51.2%, respectively, which were nearly twice higher than the nitrogen control rates of sorghum and maize. This may be because the ryegrass, purslane and collard treatments had a certain coverage in the early fallow period (21 days), which reduced the leaching volume by 23.5%, 17.1% and 26.7% compared with fallow treatment. In contrast, sorghum and maize treatments had poor coverage in the early fallow period, hence there was no significant difference in leaching volume between sorghum and maize treatments and fallow treatment. In addition, the NO3--N content in the surface soil (0-20 cm) of ryegrass, purslane and collard treatments was 40.1-52.8 mg?kg-1, while in the surface soil of sorghum and maize treatments it was 67.8-72.7 mg?kg-1. Besides, compared with sorghum and maize treatments, ryegrass, purslane and collard treatments also significantly increased the abundance of nirS type denitrifying bacteria in surface soil and nosZ type denitrifying bacteria in rhizosphere soil, which may enhance the denitrification process in soil. This may be one of the mechanisms for high nitrogen leaching control efficiency.【Conclusion】In general, ryegrass, purslane and collard as the catch crops of protected vegetable field in areas with frequent rainfall can significantly reduce nitrogen and phosphorus leaching, and collard has the best effect on nitrogen and phosphorus comprehensive control.

      • Effects of Soil Hydrothermal Response and Pools of Carbon and Nitrogen Under Straw Cover Rotation on Slope Farmland of Low Mountains and Hills

        WANG Genlin, DUAN Yan, LIU Zhengyu, WANG Nannan, GAO Yang, LI Yumei†, MENG Xianghai, WANG Wei, CAI Shanshan, SUN Lei

        DOI: 10.11766/trxb202112170583

        Abstract:

        【Objective】The main forms of soil erosion are water, wind and freeze-thaw erosion in the black soil area of Northeast China, and slope farmland is the main source of soil erosion. Human factors such as long-term plowing and straw burning or leaving the field untended and heavy use of light farming or other factors have led to the loss of surface soil, shallow cultivated layer, soil infiltration and erosion resistance of sloping farmland. This would aggravate surface runoff and soil water erosion in summer during severe rainfall. To improve the straw return rate in sloping farmland, a suitable farming method based on planting and cultivating land was proposed. 【Method】Field experiments were used to study the effects of straw mulching and rotation tillage technology (including this season straw mulching and fallow, last season straw mulching and rotary tillage) and conventional farming (straw removal and rotary tillage) on soil water and heat changes and carbon and nitrogen accumulation.【Result】The results showed that: water content in the 20-40 cm soil layer in the early stage of planting could significantly be increased with straw mulching, and the mulching fallow and mulching rotary tillage treatments increased by 26.02% and37.49%, respectively, compared with conventional tillage. At the same time, the 20-40 cm soil bulk density in mulching rotary tillage treatment was higher than that of conventional tillage and mulching fallow, which were reduced by 6.52% and 13.04%, respectively. Compared with mulching and rotary tillage, mulching and fallow could reduce the soil temperature of 0-20 cm and 20-40 cm in the early stage of crop growth by 1.57℃-1.63℃, while the soil moisture content increased by 15.25%-24.41%, which provided conditions for crop emergence and early growth. Combining straw mulching fallow tillage and mulching rotary tillage technologies increased the carbon and nitrogen content of 0-20 cm soil layer, and the organic carbon and total nitrogen reserves were increased by 11.36% and 20.51% compared with conventional tillage.【Conclusion】All of this provide a scientific basis for the implementation of protective farming techniques on slope farmland in the low mountain and hilly areas. In the future, the optimized combination of crop varieties and dwarfing and maturity promotion would promote the increase of productivity in slope farmland when implementing conservation tillage technology.

      • Changes in Soil Heterotrophic Respiration and Its Microbial Diversity during Restoration of Pinus massoniana Plantations in Eroded Red Soil Area

        JIANG Yongmeng, DENG Cui, LYU Maokui?, XIONG Xiaoling, LI Jiayu, XIE Jinsheng

        DOI: 10.11766/trxb202110240498

        Abstract:

        【Objective】The accumulation rate of soil organic matter directly restricts the improvement of productivity of Pinus massoniana (Masson pine) in the process of vegetation restoration in eroded red soil area. The way to solve this problem has been an inevitable development process of Masson pine in eroded red soil area. Heterotrophic respiration, an important part of soil carbon emission, is a key factor affecting soil organic carbon accumulation. Therefore, it is of great significance to study the effects of Masson pine plantation restoration on heterotrophic respiration and its temperature sensitivity in eroded red soil areas. This will enhance our understanding of the carbon output process and effectively increase soil organic matter accumulation in eroded red soil areas. 【Method】In this study, Masson pine plantations with different restoration years (Y0, Y14, Y31) were selected as the research objects. The effects of vegetation restoration on soil heterotrophic respiration were studied by separating and measuring different respiration components and combining with soil factors such as soil organic carbon, total nitrogen, soil temperature, water content and litter. The structural equation model of heterotrophic respiration between litter, soil temperature, soil nutrients, soil microorganisms and heterotrophic respiration were established to analyze the correlation between heterotrophic respiration and environmental factors in the process of vegetation restoration, and to explore the main factors affecting heterotrophic respiration. 【Result】The results showed that the heterotrophic respiration (RH) of the pine forests with different recovery years differed significantly. The RH in site Y31 was significantly higher than that in site Y14 and Y0. The RH in site Y0 was only 0.99 μmol?m-2?s-1, while in sites Y14 and Y31 it was 2.20 and 2.80 μmol?m-2?s-1, respectively. Temperature was the main influencing factor of the seasonal variation of heterotrophic respiration, explaining 40.6% (Y0), 62.2% (Y14) and 66.6% (Y31) of the seasonal variation, respectively. During the restoration process, the temperature sensitivity (Q10) of relative humidity increased significantly, which was 1.58, 1.93 and 1.82, respectively. The relative contributions of RH to total soil respiration in different recovery years are 77.94% (Y0), 70.84% (Y14), and 77.35% (Y31). The structural equation model showed that soil organic carbon (SOC), temperature and soil microbial diversity were the main factors affecting soil RH during the restoration of Masson pine. SOC and soil microbial abundance significantly correlated with RH, and soil temperature varied with vegetation restoration which significantly and negatively correlated with RH. 【Conclusion】The results of this study indicate that the accumulation of SOC and lack of effective physical protection during Masson pine vegetation restoration increase the decomposition of SOC by microorganisms; On the other hand, the reduction of soil environmental temperature, a continuous increase of bacteria and fungi abundance, and an increase of Proteobacteria, Ascomycota and Acidobacteria in the community further aggravate the microbes to the original strength of soil organic matter decomposition. Consequently, the continuous increase of heterotrophic respiration related carbon emissions limits the improvement of carbon sequestration efficiency of Masson pine forests. Therefore, the strong soil heterotrophic respiration in the eroded and degraded red soil area may be the key factor limiting further improvement of soil organic matter.

      • Effect of Pig Slurry Application on Crop Growth and Soil Quality of Farmland Under Rice-Wheat Rotation System

        CHEN Guangyin, CAO Hainan, WU Pei, HUANG Yan, WANG Yu, LIU Hongjiang, DONG Jinzhu, FANG Caixia

        DOI: 10.11766/trxb202109140412

        Abstract:

        【Objective】Pig is one of the most farmed breeds in China. In 2020, there were 406.50 million pigs in China and 41.13 million tons of pork were produced. Meanwhile, hundreds of thousands of tons of pig slurry and manure were produced during pig breeding in China. Many nutrient elements needed for crop growth are available in pig slurry, such as nitrogen, phosphorus, amino acids, trace elements, etc. Returning pig slurry to the field is one of the best ways for its utilization. To solve the problem of pig slurry application on farmland, studies are required to determine the optimal amount of pig slurry needed for the application and reduce the possible environmental risks which are associated with pig slurry application. 【Method】The experiments were carried out in a self-made soil column with a volume of 42.41 L and were designed with 7 treatments, including no fertilization (CK), 50% (50%W), 100% (100%W), 200% (200%W) and 300% (300%W) replacement of chemical nitrogen fertilizer by pig slurry, 50% replacement of chemical nitrogen fertilizer by pig slurry + 50% chemical nitrogen fertilizer(50%W+50%C), and 100% chemical nitrogen fertilizer(100%C). The average number of spikes, chlorophyll content, spike and straw yield, nitrogen and phosphorus content in spikes and straw, and the changes in physico-chemical properties of soil leachate and the contents of nitrogen, phosphorus and heavy metals were analyzed. 【Result】The results showed that both 50% and 100% replacement of chemical nitrogen fertilizer by pig slurry could promote the growth of rice and wheat to varying degrees and increase the yield. However, the difference between treatments was not significant. The excessive application of pig slurry caused rotten roots and dead seedlings in rice, wild growth in wheat, and increased nitrogen and phosphorus concentration in soil leachate, which increased the risk of contaminating groundwater, and some indexes even exceeded the standard of Class IV water in the National Groundwater Quality Standard (GB/T 14848-2017). Also, the massive application of pig slurry caused the accumulation of Cu, Cd and Pb in the soil whereas Zn content did not increase significantly. The above results indicate that, the replacement of chemical fertilizer by pig slurry is feasible under appropriate conditions as shown in this experiment. 【Conclusion】It is suggested that the application amount of pig slurry should not be more than 200% replacement of chemical nitrogen fertilizer which have a better effect in promoting the growth of rice and wheat, fertilizing the soil and controlling environmental pollution risk of farmland.

      • Experimental Study on The Improvement of Soil Moisture Characteristics of Coal Mine Dump by Fly Ash and Arsenic Sandstone

        ZHENG Peng, DANG Tinghui, XUE Jiang

        DOI: 10.11766/trxb202104140197

        Abstract:

        【Objective】Reclaimed soil in an open-air coal mine is highly infertile due to its poor physical and chemical characteristics. The reclamation methods usually improve soil moisture content which has important theoretical and practical significance for the reclaimed mine soil.【Method】This experiment was conducted in the Heidaigou open-air coal mine in the Inner Mongolia Autonomous Region, in which the following treatments were applied; fly ash, arsenic sandstone and dump soil. A certain mass ratio gradient was set, including 13 blended treatments denoted as L3F1, L4F1, L5F1, L1S1, L2S1, L3S1, L4S1, L5S1, L1F1S1, L2F1S1, L3F1S1, L4F1S1, L5F1S1, in which the L, F, S represented three kinds of controlled treatments. The volumetric water content of each compound soil under different water suctions was measured by the centrifuge method for the drawing of the water characteristic curve using the Gardner fitting model. The specific water capacity, field water capacity, wilting coefficient and effective water content of each treatment were also calculated.【Result】The results showed that the Gardner model was appropriate to fit the water characteristic curves of the 13 compound soils. The addition of fly ash increased the content of fine soil particles (i.e., clay and silt) by 24.11% to 37.19%, respectively, and improved the water holding capacity and water supply of soil. Furthermore, the addition of arsenic sandstone improved the water holding capacity of soil but failed to improve the water supply performance. The water holding capacity of L1F1S1 treatment and water supply performance of L3F1 treatment was the best, which was 47.6% and 40.23% higher than that of the dump soil, respectively. The field water holding capacity and available water content of LF combined treatment and LFS combined treatment were enhanced with the increase of additive proportion. When the mass ratio of soil and fly ash in the dump was 3:1 (L3F1), the maximum field water holding capacity was 18.02%. On the other hand, the maximum available water content was 13.1% with the mass ratio of soil, fly ash and arsenic sandstone of 1:1:1 (L1F1S1).【Conclusion】Overall, the comprehensive utilization of fly ash and arsenic sandstone is beneficial to improve the soil water characteristics of coal mine dump, and the soil water holding capacity and water supply capacity is better when the clay and silt contents of the soil are within the range of 30%-35%. In this experiment, the mass ratio of 1:1:1 is the best.

      • Coupling Effects of Straw and Woody Peat on Rapidly Increasing Soil Organic Matter and Crop Yield under Different Application Ratios

        ZHOU Tantan, LI Dandan, QIU Lili, XU Jisheng, ZHOU Yunpeng, TAN Jun, ZHAO Bingzi

        DOI: 10.11766/trxb202112030656

        Abstract:

        【Objective】Reclaimed soil in an open-air coal mine is highly infertile due to its poor physical and chemical characteristics. The reclamation methods usually improve soil moisture content which has important theoretical and practical significance for the reclaimed mine soil.【Method】This experiment was conducted in the Heidaigou open-air coal mine in the Inner Mongolia Autonomous Region, in which the following treatments were applied; fly ash, arsenic sandstone and dump soil. A certain mass ratio gradient was set, including 13 blended treatments denoted as L3F1, L4F1, L5F1, L1S1, L2S1, L3S1, L4S1, L5S1, L1F1S1, L2F1S1, L3F1S1, L4F1S1, L5F1S1, in which the L, F, S represented three kinds of controlled treatments. The volumetric water content of each compound soil under different water suctions was measured by the centrifuge method for the drawing of the water characteristic curve using the Gardner fitting model. The specific water capacity, field water capacity, wilting coefficient and effective water content of each treatment were also calculated.【Result】The results showed that the Gardner model was appropriate to fit the water characteristic curves of the 13 compound soils. The addition of fly ash increased the content of fine soil particles (i.e., clay and silt) by 24.11% to 37.19%, respectively, and improved the water holding capacity and water supply of soil. Furthermore, the addition of arsenic sandstone improved the water holding capacity of soil but failed to improve the water supply performance. The water holding capacity of L1F1S1 treatment and water supply performance of L3F1 treatment was the best, which was 47.6% and 40.23% higher than that of the dump soil, respectively. The field water holding capacity and available water content of LF combined treatment and LFS combined treatment were enhanced with the increase of additive proportion. When the mass ratio of soil and fly ash in the dump was 3:1 (L3F1), the maximum field water holding capacity was 18.02%. On the other hand, the maximum available water content was 13.1% with the mass ratio of soil, fly ash and arsenic sandstone of 1:1:1 (L1F1S1).【Conclusion】Overall, the comprehensive utilization of fly ash and arsenic sandstone is beneficial to improve the soil water characteristics of coal mine dump, and the soil water holding capacity and water supply capacity is better when the clay and silt contents of the soil are within the range of 30%-35%. In this experiment, the mass ratio of 1:1:1 is the best.

      • Stoichiometry of Base Cations and Silicon of Cambosols Derived from Different Parent Materials as Leached by Simulated Acid Rain

        ZHAO Yue, YANG Jinling, XU Zhe, ZHANG Ganlin

        DOI: 10.11766/trxb202202110053

        Abstract:

        【Objective】The soil acidification rate in current environment is the basis for controlling soil acidification. However, the accurate estimation of soil acidification rate is difficult due to the buffer effect of soils. The soil consumes exogenous H+ and releases base cations through mineral weathering (compensating for base cations loss and inhibiting soil acidification) and the cation exchange process (increasing exchangeable H+ and inducing soil acidification). Nevertheless, it is difficult to distinguish these processes, which leads to large errors in estimating soil acidification rate. Since silicon (Si) only comes from mineral weathering reaction and has nothing to do with cation exchange, the stoichiometry of base cations (BC: K+, Na+, Ca2+, Mg2+) and silicon release (BC:Si) during soil mineral weathering can quantify the H+ consumed through mineral weathering, which is helpful to determine accurate soil acidification rate. The purpose of this research is to explore the BC: Si difference and its causes in Udic Cambosols derived from three parent materials of Mica schist, Gneiss and Andesite. 【Method】 First of all, the physical, chemical and mineralogical properties of test soils were measured. To avoid the influence of the base cations adsorbed by soil colloid on stoichiometry of the mineral weathering process, soil exchangeable base cations were washed by elution experiment. Then, the release of base cations and silicon of soils derived from three parent materials were obtained by leaching of simulated acid rain. 【Result】The results showed that content and distribution in the profile of clay, pH, organic matters, exchangeable base cations (K+, Na+, Ca2+, Mg2+), cation exchange capacity (CEC) and mineral compositions were significantly different for different parent materials. During simulated acid rain leaching, BC:Si values of base-uneluted soils were three times more than that of base-eluted soils. Only when the exchangeable base cations adsorbed by soil colloid were eluted can obtain accurate BC:Si values. The smallest BC:Si value was in the humus surface horizon (Ah) in the same soil profile with different soil genetic horizons and the largest BC:Si value was in the parent materials horizon (C). BC:Si value of Udic Cambosols derived from different parent materials soils followed: Gneiss > Mica schist > Andesite. The mineral proportions of plagioclase, illite, chlorite, and vermiculite in soils controlled the BC:Si values. 【Conclusion】Therefore, only on the basis of corresponding BC:Si, the response degree of Cambosols with different parent materials to the acidification process can be accurately evaluated. The results can provide data support for soil acidification rate evaluation regionally.

      • Optimization of Robot System on Determining Upland Soil N2 Emission as Compared to Other Methods

        LI Chenglin, WEI Zhijun, WU Min, SHAN Jun, YAN Xiaoyuan

        DOI: 10.11766/trxb202109270525

        Abstract:

        【Objective】The massive application of nitrogen fertilizer to agricultural soils plays an important role in ensuring the world’s food supply. However, it also leads to a large amount of reactive nitrogen (N) entering the environment, which strongly interferes with the biogeochemical cycle of N and causes a series of ecological and environmental problems. As the last step of N cycling, denitrification is the predominant pathway, converting reactive N into inert N (i.e., N2). However, measuring soil N2 production from denitrification is a major challenge in terrestrial ecosystems because of the high atmospheric background N2 concentration. Recently, direct methods for measuring N2 emission rates have been developed. Among them, robotized incubation and analyzing system (Robot system) which is based on N2 free headspace (i.e., helium environment) have been widely used for measuring N2 emission in pure denitrifying culture or soil, due to its advantage on platform construction and high throughput for N2 determination. Nevertheless, frequent sampling with the small-diameter steel needle is required during the operation and determination of the Robot system, which inevitably causes leakage of N2. This seriously interferes with the determination of low N2 emission rates (i.e., background N2 flux in upland soil). Therefore, to enable the Robot system to measure background N2 emission rate in upland soil without exogenous substrate, the leakage rate of the system must be further reduced. 【Method】In this study, helium (He)-washed rubber septa, solutions prepared by He-washed distilled water and destructive sampling treatments were explored to optimize the Robot system aiming at reducing the N2 leakage therein. Additionally, results of soil N2 emission determined by the optimized Robot system were compared with those of acetylene inhibition technique (AIT) and Robotized continuous flow incubation system (RoFlow system). 【Result】Our results showed that the N2 leakage rate of the Robot system could be remarkably reduced by optimizing with He-washed septa, solutions prepared by He-washed distilled water and destructive sampling treatments. Relative to the reported N2 leakage (5.15 μL·L-1·h-1) of the Robot system, the N2 leakage rate was reduced to 0~0.8 μL·L-1·h-1 by the aforementioned treatments. Under similar treatments, the N2 emission rate measured by the acetylene inhibition method was highest, followed by the RoFlow system, and the Robot system had the lowest results. Furthermore, the optimized Robot system was capable of determining upland soil N2 emissions in response to carbon and N addition, which also had the smallest standard error (0.003~0.045 mg·kg-1·d-1) compared with the AIT method (0.34~3.29 mg·kg-1·d-1) and RoFlow system (0.41~1.02 mg·kg-1·d-1). 【Conclusion】Overall, the optimized Robot system is characterized by low N2 leakage, effective response to substrate addition and good consistency in determining soil N2 emission. In the future, it will have a favorable application in investigating background N2 emissions and the associated mechanism of upland soil.

      • Effects of Substitution of Chemical Fertilizer with Biogas Slurry and Combined with Straw on Denitrification and Nitrate Ammoniation Potential of Paddy Soil

        YANG Zhishu, XU Chuanhong, TANG Yifan, SHEN Jianhua, MENG Yan, HAN Jiangang

        DOI: 10.11766/trxb202110120550

        Abstract:

        【Objective】This study aimed to reveal the effects of biogas slurry instead of chemical nitrogen fertilizer on soil Denitrification (Den) and Dissimilatory Nitrate Reduction to Ammonium (DNRA).【Method】A field plot experiment was carried out in a typical coastal paddy field in Dongtai, Jiangsu Province. Five treatments were set up: a single application of chemical fertilizer (C), a single application of biogas slurry (B), combined application of biogas slurry and straw (BS), combined application of chemical fertilizer and straw (CS) and control (CK). The variation characteristics of soil Den and DNRA potential at different growth stages of rice plants were studied by the 15N isotope tracer technique.【Result】The results showed that: ① In the whole rice growth period, Biogas slurry instead of chemical fertilizer effectively reduced the Den intensity (1.48 μg·kg-1·h-1) and the total amount of N2O by 27% in paddy soil. Compared with the combined application of chemical fertilizer and straw, the combined application of biogas slurry and straw resulted in a significant increase in total N2O (70%). ② Looking at different growth stages, the regulation of N2O in the mature stage of the plant is particularly necessary. The N2O production in biogas slurry (B, BS) and chemical fertilizer (C and CS) treatments peaked at maturity, accounting for 70% ~ 71% and 75% ~ 92% of the total production on average, respectively. Also, the soil DNRA potential was the highest at tillering stage, and the DNRA potential of B and BS treatments were significantly higher than that of C and CS treatments. ③ The Den potential of biogas slurry or chemical fertilizer treatment was positively correlated with pH and negatively correlated with C:N. Also, the increase in C:N resulted in a decrease in Den intensity of biogas slurry instead of chemical fertilizer (i.e. treatment B).When combined with straw, the factors leading to changes in Den potential are transformed into NO3--N and NH4+-N, and the decrease of C:N leads to an increase in Den intensity.【Conclusion】Biogas slurry instead of chemical fertilizer can play a positive role in the preservation of N in soils. This study provides a theoretical basis for clarifying the impact of biogas slurry replacing chemical fertilizer and straw returning on the process of Den and DNRA in paddy soils. Also, it highlights the environmental impact as well as the exploration of biogas slurry application mode in coastal farmland.

      • Advances in Research on the Evolution and Maintenance Mechanism of Soil Fertility in Plantation

        liu chaohua, li fengqiao, liao yangwenke, li xiaogang

        DOI: 10.11766/trxb202112020653

        Abstract:

        Soil is the basic resource supporting the healthy growth of plantation and the main site for nutrient transformation and biodiversity protection. To date, the decline of soil fertility is a serious problem in plantation management in China, which is an important factor restricting the sustainable management of forestry production and increasing the vulnerability of ecological security barrier. Therefore, it is necessary to deeply understand the influence process of plantation on soil fertility, and develop key control technologies to ensure the health and primary productivity of plantation. This paper systematically discusses the maintenance mechanism of plantation on soil fertility from the aspects of soil physical and chemical environment, soil biological community characteristics and functions, and discusses the ecological processes affecting soil fertility of plantation, such as forest age structure, stand density and tree species type. In the future, more attention should be paid to the coupling mechanism of soil physical and chemical properties and biological properties of plantations under environmental changes. At present, the accumulation characteristics of soil pathogenic bacteria in large-scale plantation are unclear, and the mechanism of soil diseases affecting plantation health needs to be revealed urgently. In the future, it is necessary to further quantify the interaction model among tree health, soil biology and environment, and form a comprehensive directional regulation system of plantation health from the afforestation, process management, symptom diagnosis and soil fertility regulation, so as to ensure the sustainable and multi-objective management of plantation health.

      • Optimization of Denitrifier Method for Determination of Soil NO2--15N Abundance

        GUO Ru, WEN Teng, CAO Yacheng, ZHANG Jinbo

        DOI: 10.11766/trxb202106070299

        Abstract:

        【Objective】NO2- is a key intermediate product of several nitrogen transformation processes in soil, with low concentration and fast transformation. The combination of denitrifier method and mass spectrometry technology has been widely used in the 15N isotope analysis of NO3- or NO2- in water. 【Method】This paper aims to optimize the culture and reaction conditions of Stenotrophomonas nitritireducens denitrifier method, and to realize the specific, rapid and accurate determination of NO2--15N abundance in soil extract. Thus, we will optimize the culture method and reaction conditions, and bacterial concentration of denitrifier method, then applied this method to the soil extract.【Result】There was no significant difference in the 15N isotopic determination of NO2- samples between aerobic shaking with seed solution and microaerobic incubation of single colonies. The seed solution ensures the stability of different batches of bacteria and aerobic incubation reduces the incubation time from 7~8 days to 12~15 h. High purity N2 or He purging for 0.5 h can effectively remove O2 and blank nitrogen, but the cost of N2 purging is lower. The transfer of N2O gas to the dry gas cylinder did not affect the accuracy and precision of the determination results. However, it can prolong the sample preservation time and reduce alkali steam corrosion of the instrument pipeline. Also, using bacteria in logarithmic growth phase and adjusting the reaction system to an OD600 value of 0.3~0.9 will ensure their denitrification efficiency and reduce variation between batches. Using no more than 1 mol·L-1 KCl to extract the soil will ensure the extraction efficiency and reduce the impact on the viability of the bacteria.【Conclusion】The optimized method can accurately determine the 15N abundance of NO2- in different types of soil with a measurement accuracy of δ15N of 5~20 nmol and natural abundance value of NO2- between 0.1‰~0.9‰, with most values being less than 0.5. Also, the experimental period was greatly shortened, simplified steps and save cost.

      • Effects of Nitrogen Fertilization Combined with Straw Incorporation on Soil Protist Community

        LI Shengjun, LI Yujie, ZHAO Jianning

        DOI: 10.11766/trxb202111090520

        Abstract:

        Long-term chemical fertilization (especially nitrogen fertilization) under intensive land-management practices in agriculture is of great concern globally due to its adverse influence on the environment and human health. Returning the eco-friendly crop residues to farmland is a promising way of reducing chemical fertilizer input and alleviating environmental problems.【Objective】Protists are unicellular eukaryotes with enormous abundance and diversity, and play versatile functional roles to improve soil fertility and agricultural productivity. Thus, they comprise an integral component of soil microbiota in the agroecosystem. However, little is known about the responses of the soil protist community to nitrogen fertilization in combination with straw incorporation.【Method】Here, a fixed field trial with 2 × 4 full-factor interaction was performed to examine the variations in diversity, composition, and potential function of the protistan community using Illumina high-throughput sequencing under eight different fertilization treatments (2 straw returning groups × 4 nitrogen gradients),Also, the key forces driving the variation in soil protistan community were determined in combination with edaphic property analysis.【Result】The phyla Chlorophyta, Conosa, Cercozoa and Ciliophora were dominant in the soils for all treatments. Nitrogen fertilization diminished the diversity of soil protists, whereas straw returning in general modified such impacts, with more pronounced effects under higher nitrogen application rates. Regardless of whether straw was added, the relative abundance of Chlorophyta exhibited an overall decrease with increased nitrogen gradient. Cercozoa and Ciliophora presented an increase in proportion with the amount of nitrogen fertilizer in the straw returning group. In the current study, the protistan functional community was predominated by phagotrophs in all treatments. Compared to treatments without straw addition, the implementation of straw returning enhanced the relative abundance of phagotrophs, but suppressed the proportion of phototrophs. Protistan parasites preferred a high nitrogen input under exclusive nitrogen fertilizer, with highest proportion in N300 treatment, which was significantly higher than those in all other treatments,. Soil properties were important environmental factors determining the shifts in soil protist community, with soil organic matter and pH exhibiting the most intensive influences as revealed by redundancy analysis (RDA) and Pearson’s correlation analysis.【Conclusion】This study provides experimental evidence that nitrogen fertilization coupled with straw incorporation have consequences for the soil protist community, It also shows that the phylogenetic and functional taxa of protists are responsive to such agricultural management regime alterations. Future studies should aim at deciphering the trophic associations among microorganisms, as well as constructing agricultural soil microhabitat beneficial for crops based on reasonable fertilization regimes and utilization of biotic resources like protists.

      • Screening of Low-Cd-accumulating Rice Varieties and Derivation of Soil Cd Safety Threshold in Southern Jiangsu

        TU Feng, LI Zhenxuan, ZHANG Xumei, PAN Yunjun, KONG Cheng, SUN Yongquan, QIU Yige, WU Longhua, LUO Yongming

        DOI: 10.11766/trxb202108140363

        Abstract:

        【Objective】There are urgent requirements to solve the problem of cadmium (Cd) pollution in farmlands and rice. With the rapid economic development in Southern Jiangsu, Cd pollution in soil and rice caused by industrialization has significantly increased. The purpose of this study was to screen low-Cd-accumulating rice varieties from main cultivated varieties in Southern Jiangsu, and to deduce the local soil Cd threshold for the safe production of rice. 【Method】In this study, field plot experiments and field investigation were conducted at different sites and years. Eighteen local main cultivated rice varieties in Southern Jiangsu were selected, including 15 Japonica conventional varieties: Wuyunjing 30 (WYJ30), Suxiangjing 100 (SXJ100), Changnongjing 10 (CNJ10), Nanjing 3908 (NJ3908), Nanjing 5055 (NJ5055), Changnongjing 12 (CNJ12), Nanjing 46 (NJ46), Changnongjing 11 (CNJ11), Jiahua 1 (JH1), Changxiangjing 1813 (CXJ1813), Changnongjing 8 (CNJ8), Wukejing 7375 (WKJ7375), Zaoxiangjing 1 (ZXJ1), Yangyujing 3 (YYJ3), Zhennuo 19 (ZN19), and 3 Japonica three-line hybrid varieties: Changyoujing 6 (CYJ6), Changyou 4 (CY4) and Changyoujing 11 (CYJ11). The differences of Cd bioconcentration factor (BCF) in rice grains among these varieties were comprehensively compared, and the soil Cd safety thresholds at different pH ranges were deduced using the species sensitivity distribution (SSD) method. 【Result】The results showed that the order of grain Cd accumulation among tested varieties was consistent between field investigation and plot experiments. There were significant differences in Cd BCF among 18 main cultivated rice varieties, with a maximum difference of 4.7 times. The Cd accumulation in some varieties like NJ46 and NJ3908 was stably low. Based on the SSD method, the deduced safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard (0.2 mg?kg-1) (GB 2762-2017) under soil pH 5.0~6.5, 6.5~7.5 and 7.5~8.5 in southern Jiangsu were 0.52, 0.80 and 1.78 mg?kg-1, which were higher than the current risk screening value (GB 15618-2018). It was verified that the deduced thresholds remarkably improved the accuracy of Cd risk prediction of rice in Southern Jiangsu. 【Conclusion】Based on field plot experiments and field investigation, numerous local main cultivated rice varieties including NJ46 and NJ3908 were screened with stably low Cd accumulation capacity, stable yield and high quality, and therefore are suggested for cultivation in Cd contaminated paddy fields in Southern Jiangsu. The deduced local safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard were higher than the current risk screening value. The results have important implications for the safe utilization of Cd contaminated paddy fields in Southern Jiangsu.

      • Contrasting Effects of Biochar and Ca(OH)2 on Alleviating Plant Aluminum Toxicity during Soil Acidification: A Simulation Study

        LAI Hongwei, NI Ni, SHI Renyong, DONG Ying, YAN Jing, NKOH Jackson Nkoh, LI Jiuyu, CUI Xiumin?, XU Renkou

        DOI: 10.11766/trxb202111250567

        Abstract:

        【Objective】 With the input of acid, the lime effect of ameliorants on acidic soils is gradually weakened resulting in soil re-acidification and aluminum toxicity. As a new alternative amendment material for acid soils, the performance of biochar on alleviating aluminum toxicity during soil re-acidification is still unclear. To investigate the effect and mechanisms of biochar on alleviating aluminum toxicity during soil acidification, a comparative study between biochar and Ca(OH)2 was conducted through a simulated soil re-acidification test.【Method】 Cyclic acid leaching with HNO3 was used to rapidly simulate the soil acidification process. A root elongation experiment with maize was used to investigate the response of plant roots to soil acidification. The change in soil pH, soluble Al3+ and base cations (K+, Ca2+ and Mg2+) during soil acidification were also studied. 【Result】Cyclic acid leaching effectively simulated the process of soil re-acidification. With the increase of cyclic acid leaching time, soil pH decreased and the maize root elongation was inhibited. Compared with Ca(OH)2 treatment, biochar significantly inhibited the acidification process and alleviated adverse effects on plant roots. When acid input was simulated for 12 years, the relative elongation of maize root in biochar treatment was 18.6% higher, and the relative absorption of Evans blue was 19.6% lower than that in Ca(OH)2 treatment. On the one hand, biochar slowed down the decrease of soil pH during re-acidification through the protonation of surface anionic functional groups, and thus inhibited the activation of soil aluminum. As a result, the soil pH and the soluble Al3+ concentration in biochar treatment were 0.12 units higher and 33% lower than that in Ca(OH)2 treatment with simulated 12-year acid input, respectively. On the other hand, biochar released Mg2+ continuously during soil re-acidification. In the simulation of 12-year acid input, the concentration of Mg2+ in soil solution and uptake of Mg2+ by maize in biochar treatment was more than twice higher than that in Ca(OH)2 treatment. A higher concentration of Mg2+ can help alleviate the symptoms of aluminum toxicity in maize by regulating the physiological response of plants to Al3+. 【Conclusion】 Compared with Ca(OH)2, biochar presented more long-term potential in ameliorating acidic soils under continuous acid input. These results are of important significance for management of soil acidification.

      • Effects of Humic Acid on Fungal Community Structure in a Peanut-continuous Cropping Soil

        WEI Shiping, WU Meng, LI Pengfa, LIU Jia, LI Guilong, LIU Kai, LIU Ming, LI Zhongpei

        DOI: 10.11766/trxb202111050447

        Abstract:

        【Objective】The negative impact of soil-borne diseases on peanut is enhanced for continuous planting. Thus, green prevention and control practices on soil-borne diseases are always an important part when establishing a resource-saving and environment-friendly sustainable control technology system. As a natural stimulant, humic acid has been shown to suppress the activity of soil-borne pathogenic fungi, and the inhibitory effect has a wide range and diverse manifestations. However, valid information is still lacking about the effects of humic acid on the microbial community. The objective of this work was to investigate the response of soil fungal communities under continuous peanut planting to humic acid from different origins, and to provide a theoretical basis for researching and developing a green-effective prevention and control method on soil-borne diseases in the continuous planting soil.【Method】 Different concentrations of humic acids from mossy peat and weathered coal were respectively added to two peanut planting soils (including 1 year and 6 years continuous planting), and soils were cultured with indoor thermostatic incubation. The soil fungi community was sequenced by Illumina MiSeq PE300. PerMANOVA, correlation analysis, and other methods were used to explain the effect of humic acid on the soil fungi community. 【Result】The results showed that the addition of humic acid had a significant effect on the fungal community structure of six years planting soil, while it had no significant effect on one-year planting soil. The concentration of humic acid both had a significant effect on the fungi community structure of the two planting soils. Effects of humic acid on soil fungi community structure at each culture time were as follows: humic acids significantly changed the fungi community structures of one-year planting soil at 94 d and 193 d, and of six years planting soil at 193 d. Also, the concentration of humic acids had significant effects on the fungi community structure of the two planting soils during the whole culture process. Humic acid also significantly changed the relative abundance of some fungi at the genus level. The effect of humic acid on soil fungal function can be mainly attributed to its significant alteration of the compositions of fungal functional trophic types in the two planting soils. It was also observed that the relative abundance of plant pathogens in soil decreased significantly with an increase in the concentration of humic acid. Spearman correlation analysis further detected that the relative abundances of Fusarium spp. and Rhizoctonia spp. were significantly negatively correlated with the concentration of humic acid, while the relative abundance of Penicillium spp. was significantly positively correlated. The correlation coefficients were -0.270, -0.138, and 0.172, respectively. 【Conclusion】The appropriate concentration of specific humic acid could significantly change the soil fungi community structure and functional trophic composition in peanut soils, especially in reducing the relative abundance of plant pathogens. Results of this study could provide a direct theoretical basis for expanding the application of the ecological function of humic acid, and provide a new perspective for researching and developing efficient green prevention and control technology of soil-borne diseases.

      • Carbon Storage Estimation of Coastal Wetlands in China

        LI Jingtai, YAN Dandan, YAO Xiuying, XIE Siying, LIU Yao, SHENG Yufeng, LUAN Zhaoqing

        DOI: 10.11766/trxb202106290335

        Abstract:

        【Objective】Rapid increase in the concentrations of greenhouse gases leads to an increase in global warming. The coastal wetland ecosystem has been identified as an important place to fix atmospheric carbon dioxide because of its powerful carbon sink function. Thus, this study aimed to quantitatively assess the temporal and spatial changes of carbon storage in coastal wetlands in China, explore its influencing factors, and augment current global warming management practices. 【Method】Remote sensing data preprocessing, vegetation index calculation and land cover type extraction were carried out based on the data of Landsat atmospheric correction surface reflectance from 1987 to 2020 provided by Google Earth Engine, and then the carbon density data of coastal wetlands in more than 30 literature were collected. Combining remote sensing quantitative inversion with the life zone method, the soil carbon reserves and biomass carbon reserves of coastal wetlands in China were calculated to research the temporal and spatial dynamics of carbon reserves in coastal wetlands in China over 30 years. 【Result】The results showed that: (1) Saltmarsh wetlands were mainly distributed in the northern coastal area, tidal flats in the eastern coastal area, and mangrove wetlands in the southern coastal area; (2) The spatial distribution of carbon density of coastal wetlands in China was quite different. Also, the maximum biomass carbon density, soil carbon density and total carbon density all existed in the region of Shankou mangrove national nature reserve. The values of maximum biomass carbon density, soil carbon density and total carbon density were 220.21 t·hm-2, 130.46 t·hm-2, and 350.46 t·hm-2, respectively. Comparatively, the carbon density of coastal wetlands in southern coastal wetlands was significantly higher than that in northern and eastern coastal wetlands; (3) It was observed that the total carbon storage of coastal wetlands in China showed a decreasing trend as a whole, and its change trend was consistent with the soil carbon reserves. The biomass carbon storage had an increasing trend, with the maximum value of 5.02 Tg, and the soil carbon storage decreased first and then increased, with a maximum value of 35.54 Tg. Also, the total carbon reserves in the northern coastal region and eastern coastal region were greater than that in the southern coastal area. In addition, biomass carbon storage in the northern coastal region showed a decreasing trend, while biomass carbon storage in the eastern and southern coastal areas showed an increasing trend. The soil carbon storage in the northern coastal area, the eastern and southern coastal areas all had a decreasing trend. 【Conclusion】The results estimated in this study are comparable with those published in previous literature. Climate, vegetation and land-use change lead to a decrease in carbon storage in a coastal wetland. Human activities dominated by reclamation are the main factors affecting the dynamics of carbon storage in coastal wetlands. This paper provides a theoretical basis for effectively evaluating the carbon sequestration capacity of coastal wetlands, Also, it outlines suggestions for emission reduction, guidelines for increasing carbon sequestration measures, guides for coping with climate change, and decision support for coastal wetland ecosystem management and ecological restoration of degraded wetlands in China.

      • Cultivated Land Quality Evaluation Method and Demonstration Based on Improved Grey Target Model

        NIE Yan, HE Xinying, WANG Pu, YIN Chen, YU Lei

        DOI: 10.11766/trxb202109170501

        Abstract:

        【Objective】Cultivated land is a special public resource and the most precious natural resource, which has a fundamental and guaranteeing role in national food security. As an important means to measure the internal basic conditions and external utilization level of cultivated land, cultivated land quality evaluation is the basis for grasping the status quo of cultivated land quality and promoting sustainable use of cultivated land resources. 【Method】Based on the needs of the “triad” protection of cultivated land, we applied the Criteria Importance Though Intercriteria Correlation(CRITIC) method to improve the gray target evaluation model. Also, we proposed a new method for the evaluation of county-level cultivated land quality based on the triple quality dimension including soil quality, ecological quality and management quality. The Chibi City was taken as the case study. 【Result】Results show that the organic matter content and 17 others indicators can characterize the multi-functional quality level of cultivated land under the triple quality dimensions of soil, ecology and management. The quality of cultivated land in Chibi City was at an upper-middle level, and the range of bullseye was 0.66~0.85. Furthermore, the regional spatial difference of cultivated land quality was large and the quality grade of cultivated land in Chibi City was mainly two and three, accounting for about 80.49% of the total cultivated land area. The cultivated land with a higher quality level was mainly distributed in the northwest and east of Chibi City while with a lower quality level was predominant in the central and northern urban areas and Shenshanzhen in the northeast. The difference in cultivated land management quality in Chibi City was small, soil quality and ecological quality were more restrictive to the comprehensive quality of cultivated land. 【Conclusion】The evaluation results of this study were consistent with the existing cultivated land quality grade evaluation results. This indicate that the improved gray target evaluation model was not only more objective in the weighting and evaluation process, but also conducive to measuring the single-dimensional quality of cultivated land. The improved gray target evaluation model was an important supplement to the existing cultivated land quality evaluation methods. This research can provide theoretical and methodological references for the evaluation of cultivated land multi-functional quality, which is in line with the new perspective of cultivated land quality evaluation in the new era.

      • Simulation of Water and Vapor Fluxes in Soil Profile of Apple Orchard in Loess Area

        WAN Hua, GAO Xiaodong, ZHAO Xining, YANG Min, HE Nana, YANG Bo

        DOI: 10.11766/trxb202107090356

        Abstract:

        【Objective】The loess area is arid with little rain and the soil is loose and porous. The water vapor in this area may play an important role in profiling water migration. Thus, it is important to study and understand the cyclic migration law of soil water vapor flux in unsaturated zone for realizing the sustainable development of water resources in arid regions. 【Method】To explore the flux transfer rule of liquid water and steam water in loess profile, based on the high-frequency in-situ monitoring test of dryland apple orchard profile (0-200 cm) in Loess area, the simulation of water-vapour-heat-air coupling STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was adopted in this study. 【Result】Results show: (1) STEMMUS model reliably reproduced the dynamic changes of soil moisture (d was between 0.81 and 0.98, NRMSE was between 5.5% and 15%) and soil temperature (d was between 0.98 and 0.99, NRMSE was 1.4% and 4.6%) in the profile of dryland apple orchard. This showed good agreement with the simulation of apple tree evapotranspiration (d was between 0.92 and 0.96). (2) Rainfall had significant effects on matrix potential gradient, temperature gradient, liquid water and water vapor flux. The transport of liquid water and vapor water was mainly driven by the matrix potential gradient and temperature gradient, respectively. During the study period, the maximum recharge depths of the soil moisture was 100 cm and 160 cm, respectively, which indicates that soil water could migrate to deeper soil through downward vapor water. 【Conclusion】STEMMUS model considering soil spatial heterogeneity significantly improves the simulation accuracy and reveals the migration law of water vapor flux in loess profile. The research results can deepen the understanding of water migration in the loess profile.

      • Hydrodynamic Characteristics of Concentrated Flow Under Different Angles Between Rock and Slope in the Karst Trough Valley Area

        ZENG Rongchang, ZHANG Yuqi, HE Binghui, LI Tianyang, ZHANG Haixiang

        DOI: 10.11766/trxb202107190368

        Abstract:

        【Objective】The angles formed by exposed rocks and slope surface in a Karst trough area significantly change the hydrodynamic characteristics of the concentrated flow caused by surface runoff convergence. This process of rill erosion is closely related to hydrodynamic characteristics. Thus, it is essential to explore the hydrodynamic characteristics of concentrated flow erosion on a slope at different angles between the rocks and slopes in a Karst Trough Valley area. 【Method】An indoor scouring experiment was designed having six angles between rock and slope, three slope gradients and three inflow rates to study variations of soil erosion rate and hydrodynamic parameters.【Result】The results showed that with scour duration going on, the soil erosion rate first decreased and then tended to be stable. Also, the stream power and shear stress fluctuated but the trend was not obvious. It was also observed that the unit stream power gradually decreased while the unit energy gradually increased. When the angle was 150°, the average soil erosion rate was largest at 0.078 kg·m-2·s-1. With the increase in angle, the shear stress, stream power and unit energy decreased at first and then increased while the unit stream power decreased as a whole. Under the experimental conditions, the soil erosion rate, flow shear force, flow power and unit flow power increased with change of slope gradients and inflow rates. Importantly, the unit energy of the flow cross-section increased with an increase in inflow rates, but this change was not obvious with the slope gradients. The differences of hydrodynamic indexes among the angles were significant (P<0.05). The relationship between soil erosion rate and shear stress (R2=0.603), stream power (R2=0.600) and unit stream power (R2=0.583) was better described by the power function equation, while the relationship between soil erosion rate and unit energy of flow section was better described by linear equation (R2=0.294). Nevertheless, it was better to use shear stress to describe the soil erosion rate on the slope with different angles between rocks and slope in Karst Tough Valley area. 【Conclusion】This study may provide a theoretical basis for revealing the hydrodynamic mechanism of concentrated flow erosion under different angles between rocks and slopes in a Karst Valley area.

      • Effects of biogas slurry instead of chemical fertilizer on soil arthropod community in paddy field

        TANG Qi, CAO Lei, QIAN Jiannan, TANG Yifan, SHEN Jianhua, HAN Jiangang

        DOI: 10.11766/trxb202109240513

        Abstract:

        【Objective】Soil arthropod is an important part of the soil ecosystem. They play an important role in decomposing organic matter, improving soil physical and chemical properties, improving soil fertility and promoting plant nutrient absorption. The arthropod community is sensitive to fertilization management and is, therefore an important indicator reflecting the health and stability of the farmland ecosystem. 【Method】Soil samples were collected from experimental plots of reclaimed paddy fields in Jiangsu Tidal Flat, which has been running for 6 years. The plots were treated with biogas slurry instead of chemical fertilizer (0%, 33%, 66% and 100%). The collected samples were, analyzed for the effects of each treatment on species, quantity, community density and diversity of soil arthropods, and their relationship with the changes of soil properties. 【Result】In the treatment of biogas slurry instead of chemical fertilizer, 1024 soil animals were collected, belonging to 9 classes and 18 groups. The results showed that the dominant groups of soil arthropods in the paddy field under each fertilization treatment were Prostigmata, Collembola and Oribatida, accounting for 45.44%, 20% and 13.38% of the total density, respectively. Biogas slurry instead of chemical fertilizer (i.e. combined application of biogas slurry and chemical fertilizer) is beneficial for improving the density, diversity index and richness index of soil arthropods. When the ratio of biogas slurry to chemical fertilizer was 66% (the total amount of N applied was 225 kg·hm-2), the density, diversity index and richness index of soil arthropods were significantly higher than those of pure chemical fertilizer (the ratio of biogas slurry to chemical fertilizer was 0) (P < 0.05). Compared with pure chemical fertilizer, it increased by 129.25%, 8.67% and 34.78%, respectively. Correlation analysis showed that soil organic carbon and total nitrogen were the main factors affecting soil arthropod density in paddy fields. 【Conclusion】The combined application of biogas slurry and chemical fertilizer has a significant effect on the soil arthropod community in paddy fields. From the effect of different proportions of biogas slurry replacing chemical fertilizer on soil arthropod density and community structure, the combined application of biogas slurry and chemical fertilizer is recommended instead of replacing chemical fertilizer.

      • Promising Applications of Artificial Humification and its Products in Agricultural Production

        LI Shunyao, QI Xuemin, CHEN Meihua, YANG Wei, LI Yucheng

        DOI: 10.11766/trxb202110080469

        Abstract:

        Humic substance (HS) is the major component of soil organic matter and chemically can be depicted as a collection of diverse, relatively low-molecular-mass components of organic molecules, forming dynamic associations and stabilized by hydrophobic interactions and hydrogen bonds on the nanometer scale. The physiological effects of HS are widely documented and summarized as a result of enhancing nutrient use efficiency, aiding assimilation of both macro and micronutrients, and stimulating plant growth by induction of carbon, nitrogen, and secondary metabolism. Based on the formation mechanism and multifunctional properties of natural HS, scientists have applied HS to extracellular electron transport, environmental repair, cellular stress, and plant growth promotion. However, due to the limited supply of natural extraction sources of HS such as lignite, weathered coal, and peat, the market supply-demand of HS is increasing year by year. Given that the molecular structures of lignin and its derivatives are similar to natural HS, it is important to ask the question of whether artificial humification methods can be used to accurately control the oxidative decomposition of large-molecular lignin and/or the radical coupling of its small-molecular derivatives to synthesize humic-like products. Another important factor to consider is whether the synthesized products can match and even surpass the effects and functions of commercial HS. This creative idea has great commercial value and application prospects for realizing a continuous increase in agricultural production and income in China. In this review, we briefly generalized the sources, structure characteristics, and functional attributes of natural HS. The latest concept, mode, and mechanism of artificial humification by the use of macromolecule lignin and its derived-small phenolics are discussed, and the differences between artificial humification products and natural HS are also compared. It is confirmed that both artificial humification products and natural HS have C, H, O, N, and S elements, but the content of N in natural HS is higher than that of artificial humification products. In addition, they both contain phenolic ?OH, ?COOH, and aromatic components. Compared with artificial humification products, natural HS has more aromatic structures, but fewer oxygen-containing groups. Moreover, we explored the application values of artificial humification products in agricultural production. The agronomic effects of artificial humification products are extremely significant. On the one hand, artificial humification products can ameliorate soil physicochemical properties, increase soil fertility and water-holding capacity. On the other hand, these humic-like products are also able to serve as plant nutrient pools for promoting crop growth and development, improving nutrient use efficiency and crop yield. Therefore, the practical applications of artificial humification products are of great significance for agricultural production. At present, artificial humification techniques such as chemical oxidation, hydrothermal reaction, bio-composting, Fenton reaction, and fungal laccase-catalyzed oxidation have displayed a great application potential in the precise control of humic-like substance synthesis. In particular, fungal laccase exhibits unique advantages in humic-like substance synthesis due to its dual mechanism of oxidative decomposition and radical coupling. The humification reactions induced by fungal laccase have the characteristics of high catalytic efficiency, simple and controllable operating conditions, low energy requirements, and environmental protection, thus can be used to synthesize a variety of humic-like products. Also, the advantages and disadvantages, process paths, and main control factors of these humic-like substance synthesis technologies are summarized. Hence, this study provides theoretical support and technical guidance for researchers to conquer the artificial humification of lignin and its derivatives and the technology bottleneck of its large-scale application.

      • Determination of Wilting Coefficient by Using the Plant Gas Exchange Parameters

        ZHOU Gu, LI Yangyang, FAN Jun

        DOI: 10.11766/trxb202110140423

        Abstract:

        【Objective】The wilt coefficient is a key factor in determining the effective soil water range, reserves and availability to plants. However, the existing wilting coefficient based on plant morphological changes has the disadvantages of unclear physiological significance and is difficult to determine in the field. 【Method】To this end, in this study a pot experiment under dry-down drought was used to determine the wilting coefficients of 4 plant seedlings (Glycine max L., Helianthus annuus L., Medicago sativa L., and Leymus chinensis (Trin.) Tzvel) grown under two soil textures (loessial soil in the Loess Plateau and red soil in the southern hilly area). We evaluated the dynamic response of leaf gas exchange parameters to changes in soil moisture content, the relationship between the lower threshold of soil moisture determined based on plant gas exchange parameters, and the wilting coefficient. 【Result】The results showed that: (1) Soil texture and plant drought resistance significantly affected the wilting coefficient of plants and the corresponding soil water potential at permanent wilting. The wilting coefficients of all four plants were greater on the red soil than on loessial soil. Importantly, the stronger the drought resistance of a plant, the lower its wilting coefficient. The wilting coefficients of the four plants under loessial soil were 0.083 cm3?cm-3 (Helianthus annuus L.)> 0.081 cm3?cm-3 (Glycine max L.)> 0.072 cm3?cm-3 (Leymus chinensis (Trin.) Tzvel)> 0.060 cm3?cm-3 (Medicago sativa L.). Also, the wilting coefficients under red soil were 0.188 cm3?cm-3 (Helianthus annuus L.)> 0.180 cm3?cm -3 (Glycine max L.)> 0.174 cm3?cm-3 (Leymus chinensis (Trin.) Tzvel)> 0.172 cm3?cm-3 (Medicago sativa L.). (2) The soil moisture lower threshold determined by using a cubic function to simulate the change of stomatal conductance was highly consistent with the measured wilting coefficient.【Conclusion】Thus, the wilting coefficient could be estimated indirectly based on plant gas exchange parameters.

      • The Surface Properties of Lou Soil with Different Phosphorus Levels and their Effects on the Loss of Phosphorus

        HU Liang, DU Wei, CHANG Bokun, CAO Gang, YANG Xueyun, LÜ Jialong

        DOI: 10.11766/trxb202107070349

        Abstract:

        【Objective】This study was designed to identify the surface electrochemical characteristics of Lou soil with different phosphorus levels and to study the transportation processes of phosphorus in the soil solid-liquid phase. Also, the relationship with soil surface properties was investigated and the change of surface properties of Lou soil under controlled electrolyte concentration and its internal relevance with phosphorus loss were clarified. 【Method】The number of soil particles and phosphorus loss of Lou soil under different electrolyte concentrations was obtained by rainfall simulation test. The surface chemical properties of the soil were determined by combined measurement and analysis of surface properties. Also, the surface electrochemical properties of Lou soil with different phosphorus levels and their effects on soil phosphorus loss under the condition of long-term localized application of phosphate fertilizer were studied. 【Result】The results show that: (1) The total phosphorus content of Lou soil treated with long-term application of phosphate fertilizer is 2.46 times larger than that of Lou soil treated without phosphate fertilizer. However, the former’s surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge number were lower than those of Lou soil without the application of phosphorus; (2) For Lou soils with different phosphorus levels, the cumulative loss of soil particles and phosphorus tended to intensify with an increase in the surface potential (absolute value) of soil particles. There was a linear positive correlation between the cumulative loss of particulate phosphorus (PP) and the cumulative loss of soil particles; (3) The surface potential (absolute value) of Lou soil with lower phosphorus content was larger than that of Lou soil with higher phosphorus content, and the electrostatic repulsion between soil particles was larger, resulting in poor stability of soil aggregates and more cumulative loss of soil particles and their attached phosphorus; (4) Under the experimental conditions, the phosphorus loss in Lou soil was dominated by PP, accounting for 81%-99% of total phosphorus loss, and the proportion of dissolved phosphorus was extremely low. 【Conclusion】Long-term application of phosphate fertilizer can change the surface properties of Lou soil, and effectively maintain the stability of soil aggregates and attached phosphorus during rainfall. This study provides a new idea for environmental risk prevention and control of the long-term phosphorus application soil.

      • Desorption and Migration Characteristics of Cu/Cd Composite Contaminated Soil under different pH/Ionic Strength

        LI Jing, LIN Qing, XU Shaohui

        DOI: 10.11766/trxb202108080413

        Abstract:

        【Objective】Some changes in the external environment are often observed after the remediation of heavy metal polluted soils with solidification stabilization technology. Thus, an important scientific question worth discussing is whether the inactivated heavy metals will be released again and migrate in the soil, causing pollution risk, and under what conditions.【Method】In order to reveal the effects of different chemical factors on the activation and migration of heavy metals in contaminated soil, the desorption and migration behavior of Cu2+ and Cd2+ in soil under different ionic strength, pH and cation types (Ca2+, Na+) were studied by laboratory soil column experiments.【Result】In general, the peak leaching concentration of Cu2+ and Cd2+ increased with the increase in ionic strength. Using CaCl2 as a leaching agent, the desorption capacity of Cu2+ and Cd2+ increased at 0.005, 0.01, 0.05 and 0.1 mol·L-1 CaCl2, and the desorption capacity of Cd2+ was higher than that of Cu2+. However, 0.5 mol·L-1 CaCl2 inhibited the desorption of Cd2+ and the desorption of Cu2+ was higher than that of Cd2+. When pH decreased, the desorption of Cu2+ and Cd2+ increased, that is, the acidic environment was conducive for the desorption of Cu2+ and Cd2+. However, the concentration peak of Cu2+ and Cd2+ at pH 3 was smaller than that at pH 4 and 5. Ca2+ was more favorable for the desorption of Cu2+ and Cd2+ than Na+, but NaCl solution was more favorable for the desorption of Cu2+ at 0.005 mol·L-1. Also, the concentration of Cu2+ in the leaching stage with deionized water was higher than that in the leaching stage with CaCl2. In addition, soil particles exhaled at 0.005, 0.05 and 0.5 mol·L-1 NaCl, and the flow rate decreased at 0.05 and 0.5 mol·L-1 NaCl.【Conclusion】The increase in ionic strength, decrease in pH and presence of divalent cations were beneficial to the desorption and migration of heavy metals in soil. This study provides a theoretical basis for soil remediation and heavy metal release after soil remediation.

      • Effects of Paddy Rice Cultivation History on Soil Physical Properties and Water/Nitrogen Distribution in the Intermediate Zone between Paddy Field and Bund

        CHEN Lu, ZHANG Hailin, YI J, LIU Xiuyun, LIU Muxing, LI Shenglong, ZHOU L

        DOI: 10.11766/trxb202104150199

        Abstract:

        【Objective】Lateral seepage around the paddy bund is an important pathway for water loss in the paddy rice field. Revealing the evolution process of soil physical properties and the characteristics of soil water and nitrogen distribution in the intermediate zone between paddy field and bund is important. This is crucial for understanding the mechanism of water and nitrogen loss in the intermediate zone. 【Method】The intermediate zone between paddy field and bund with a cultivation history of 2 y, 19 y, and >100 y was considered for this study. Soil properties, including soil bulk density, equivalent porosity, soil water retention curve, saturated hydraulic conductivity (Ks), soil water content and soil nitrogen concentration were determined through field sampling and laboratory analysis. The evolution process of soil physical properties and the mechanism of water and nitrogen loss in the intermediate zone were evaluated. 【Result】The paddy rice cultivation history affected soil physical properties. With the cultivation history extending, the difference in soil bulk density between paddy field plow layer (PL) and paddy bund surface layer (SL), and between paddy field plow pan (PP) and paddy bund hard pan (HP) increased. The microporosity (with diameter <0.03 mm) in PL and SL increased with paddy rice cultivation history, while the macroporosity (with diameter >0.3 mm and >0.03 mm) decreased in other soil layers for both in paddy field and bund. This showed a quicker decrease rate in the paddy field than for the bund. Differences in soil water holding capacity (SWHC) between paddy fields and bund were identified in the measured water suction range (0~100 kPa). Similar SWHC was observed between PL and SL in both 2 y and 19 y paddy rice fields, while a much higher SWHC was found in PL than SL in >100 y paddy rice fields. Also, a similar SWHC between PP and HP were identified in both 2 y and 100 y paddy rice fields, while a much higher SWHC was found in PP than HP in the 19 y paddy rice field. A higher SWHC was observed in the paddy bund subsoil layer (BSL) than the paddy field subsoil layer (FSL) for both 19 y and >100 y paddy rice fields. With paddy rice cultivation history extending, the differences in Ks between PL and SL decreased, while it increased between PP and HP. For example, the Ks in PP was 1.10, 6.90, and 6.32 times that in HP for 2 y, 19 y, and >100 y paddy rice fields, respectively. Also, a much higher Ks was observed in bund than the field for >100 y paddy rice field, while no significant differences were observed for the other two fields. The soil water and nitrogen distribution patterns were affected by the evolution of soil physical properties in both paddy fields and bund. Also, a higher soil water content and soil nitrogen concentration were observed in 19 y and >100 y paddy rice fields than in 2 y paddy rice fields, which was mainly accumulated in the PL for both 19 y and >100 y paddy rice fields. 【Conclusion】For the young paddy rice field, soil water and nitrogen rapidly seepage from both paddy fields and bund identically. With the paddy rice cultivation history extending, soil water and nitrogen are expected to be lost more quickly from the paddy bund than the field. For >100 y paddy rice fields, the PP in the newly built bund will degrade with time, then the paddy bund will be the key site for soil water and nitrogen lose again. Therefore, the soil water and nitrogen loss from the paddy bund should be given more attention, and the focus should be more on old paddy than young paddy rice fields.

      • Continuous Multi-year Application of Chinese Milk Vetch in Paddy Soil and Its Effect on Soil Aggregates Distribution and Their Carbon and Nitrogen Content

        WANG Hui, HAN Shang, TANG Shan, CHENG Wenlong, BU Rongyan, LI Min, WU Ji, WANG Yunqing, CAO Weidong

        DOI: 10.11766/trxb202106090303

        Abstract:

        【Objective】The application of Chinese milk vetch to paddy soil is an effective practice to improve soil fertility and maintain high and stable yields in South China. The soil aggregates distributions and their carbon and nitrogen content may be influenced by the continuous multi-year application of Chinese milk vetch.【Method】We investigated the effects of 12 years of Chinese milk vetch returned to soil on soil aggregate size distribution and aggregate-associated carbon and nitrogen by setting with six treatments including CK (no fertilizers and no Chinese milk vetch applied), GM0 (fertilizer only) and four gradients of Chinese milk vetch applied (GM1-4). The aggregate size distribution and the content and storage of organic carbon and nitrogen in the soil aggregate were analyzed. Also the types and relative intensity of organic functional groups in different size classes were determined using Fourier Transform Infrared spectrometer (FTIR).【Result】The results showed that the >2 mm soil aggregate was dominant (61.12%~68.53%) and followed by the 2~0.25 mm fraction. The application of Chinese milk vetch increased the percentage of the soil aggregate size (>2 mm) by 5.93%~9.91%. Also, the contents of organic carbon and total nitrogen in the >0.053 mm aggregates increased with the application rate of the treatment. There was a significant positive correlation between the contents of organic carbon and total nitrogen and the application rates of Chinese milk vetch. Interestingly, the application of Chinese milk vetch increased the total storage of organic carbon and nitrogen by 19.42%~37.09% and 22.31%~40.13%, respectively. Moreover, the distribution of organic carbon and nitrogen in >2 mm soil aggregate was also increased after the treatment. FTIR spectroscopic analysis revealed that the relative contents of aliphatic and aromatic organic carbons in soil aggregates were increased after treatment, and there was a significant positive correlation between the N-H functional groups and the application rate of Chinese milk vetch. In addition, the relative intensities of 1 630/2 850+2 940 and 1 720/2 850+2 940 in different soil aggregates were increased. There was a significant positive correlation between the values of the relative intensity of 1 630/2 850+2 940 in both aggregate sizes of >2 mm and 2~0.25mm and the application of Chinese milk vetch.【Conclusion】The application of Chinese milk vetch to paddy soil improved the distribution of soil aggregates, increased the activity and stability of organic carbon, and enhanced the organic carbon and nitrogen storage in soil aggregates. These positive impacts of Chinese milk vetch played an important role in enhancing paddy soil fertility.

      • Experimental Study on Electrochemical Characteristics of Acid Soil Amended by Biochar

        YANG Caidi, LIU Jingjing, LU Shenggao

        DOI: 10.11766/trxb202106070300

        Abstract:

        【Objective】Climate change and the continuous impact of high-intensity human activities are intensifying soil acidification and has caused serious harm to the ecological environment and agricultural production. In recent years, studies on acid soils have focused on the effects and related mechanisms of soil conditioners on physicochemical properties and crop production, but the combined application of electrochemistry theory and other interdisciplinary principles have been given less attention. Electrochemical impedance spectroscopy (EIS) is an electrochemical measurement method using small-amplitude sinusoidal potential (or current) as a disturbance signal. Its application in the soil field has attracted much attention. In this study, EIS was combined with soil physical and chemical properties to analyze the electrochemical mechanism of biochar in improving acid soils. 【Method】A field study was conducted to amend acid soil by applying biochars produced from five biomass materials (rice straw, maize straw, wheat straw, rice husk, and bamboo). The EIS was used to study the influence of different biochars on the electrochemical characteristics of acid soil. 【Result】Results showed that the equivalent circuit topology structure was the same in different biochar-amended treatments, but the circuit component parameters were different. The equivalent circuit model was the charge transfer resistor R3 and diffusion resistor Rw at the electrode-solution interface in series, and in parallel with CPE. This part was connected in series with the soil porous layer resistor R2, and then in parallel with the soil porous layer capacitor C1. Finally, it was connected in series with pore solution resistor R1. The addition of biochar had regular effects on Nyquist and Bode diagrams. The Nyquist diagram was in the form of arcs in the high-frequency region and oblique lines in the low-frequency region. The intercepts of each curve and x-coordinate corresponded to the resistance R2 of the soil porous layer in an equivalent circuit, and a radius of each to a charge transfer resistance R3. In the Bode diagram, the impedance modulus of the modified soil amended with different biochars tended to decrease as the frequency increased. By fitting the equivalent circuit with Z-view software, it was found that the influence of different biochars on the parameter values of each element was related to changes in soil physicochemical properties. The addition of biochar increased soil contents of total soluble salts and CEC, and the concentration of free-moving ions increased, thus the electrochemical characteristics showed that the pore solution resistance R1 decreased. Since biochar was almost non-conductive, the conductive capacity of improved soil decreased, and the electrochemical characteristics showed that resistance R2 of the soil porous layer increased while capacitor C1 decreased. The cations of acid soil neutralized by biochar slowed down the process of charge transfer, increased the reaction resistance, and weaken the ability to store charge. Thus, this reduced the reaction speed and made the system more stable. The electrochemical characteristics were shown as the increase of transfer resistance R3 and diffusion impedance coefficient W, as well as the decrease of CPE-T value. 【Conclusion】The decrease of R1 indicated the increase of soil water-soluble salt content and CEC. The increase of R2 and the decrease of C1 indicated that the conductivity of the soil medium system decreased. The changes of R3, W and CPE-T indicated the charge transfer ability and overall stability of the soil system. The fitting parameters revealed the influence of modified acidification on soil pH and soluble base ions content to a certain extent, which enriched the scope of electrochemical impedance spectroscopy (EIS).

      • Application of Generalized Linear Geostatistical Model for Digital Soil Mapping in A Typical Subtropical Hilly Area

        HAO Chenkai, SUN Xiaolin, WANG Huili

        DOI: 10.11766/trxb202107290386

        Abstract:

        【Objective】Digital Soil Mapping (DSM) is receiving more attention and becoming widely used. Its methods mainly include environmental correlation-based models, spatial auto-correlation based models, and a mixture of these two kinds of models. The mixed model is expected to be advantageous over the single models. A generalized linear geostatistical model (GLGM) is a kind of mixed model. Compared with the commonly used mixed model, i.e., regression kriging (RK), GLGM has advantages such as having random effects to account for the non-stationarity of soil variability. However, GLGM is seldomly used due to its major disadvantages, i.e., complicated computation. 【Method】In this study, within a small hilly area (3.03 km2) in Gaofeng Forest of Nanning, Guangxi, generalized linear mixed model (GLMM) and its combination with ordinary kriging (OK), i.e., GLGM, were used to predict the spatial distribution of soil organic carbon (SOC), pH, clay and cation exchange capacity (CEC). Performances of the two models were then compared with commonly used models, including multivariable linear regression (MLR), geographically weighted regression (GWR), regression forest (RF), OK, RK and generalized additive model (GAM). 【Result】The results showed that GLMM had higher accuracy in predicting clay, while GLMM and GLGM had medium accuracy in predicting CEC. Further, GLMM and GLGM had lower accuracy in predicting SOC and pH. 【Conclusion】Based on the adjusted R2 of the linear regression model, nugget effect and global Moran’s I, it is concluded that GLMM and GLGM are appropriate when there is a low adjusted R2 of linear soil-landscape regression (less than 5%), weak spatial auto-correlation of soil (nugget-to-sill ratio large than 71%), and strong local spatial variability of soil (Moran’s I less than 0.09), e.g., clay in this paper. Otherwise, GLMM and GLGM are not appropriate, e.g., for SOC and pH in this paper. For the high spatial heterogeneity and multi-scale variability of soil, we think that GLMM and GLGM are promising for DSM, although more studies are needed to improve the efficiency of GLMM and GLGM modelling.

      • Effects of Iron Oxide on the Adsorption and Desorption of Se(Ⅳ) in Selenium-rich Soils of Guangxi

        huangjinlan, jiangdaihua, wangmingshi, huangxuejiao, denghuawei, huangzhigang, dengyusong

        DOI: 10.11766/trxb202110250434

        Abstract:

        【Objective】The influence of free iron oxide on the adsorption and desorption of Se(Ⅳ) in a lateritic red soil and red soil in the selenium-rich area of Guangxi was studied.【Method】The adsorption and desorption characteristics of Se(Ⅳ) in the soil before and after removing free iron oxide were compared by isothermal adsorption and desorption experiments. Zeta potential, scanning electron microscopy and energy spectrum analysis and Fourier transform infrared spectroscopy was used to explore the influencing mechanism.【Result】The results showed that the adsorption process for Se(Ⅳ) fitted the Langmuir and Freundlich models, with correlation coefficients ranging between 0.920~0.995. After removing free iron oxide of red soil and lateritic red soil, the zeta potential became more negative and changed from -24.42 and -18.06 mV to -33.06 and-26.43 mV. Also, the specific surface area was decreased. This observation correlated with the lower adsorption capacities of the soils after the removal of free iron oxide. Hence, the order of maximum adsorption capacity was: lateritic red soil (1,399 mg·kg-1)> red soil (1,337 mg·kg-1)> DCB-treated lateritic red soil (444 mg·kg-1)> DCB-treated red soil (352 mg·kg-1). The desorption rates of the tested soils were between 2% and 7%, while that of DCB-treated soils were higher than that of the original soils. The FTIR peak fitting analysis showed that the soils reacted with selenium mainly through the oxygen-containing groups such as -OH, Fe-O and C=O. After the removal of iron oxide, the effect of Fe-O in the adsorption was weakened or disappeared.【Conclusion】Free iron oxide can significantly increase the adsorption capacity and strength of soil for Se(Ⅳ) and reduce the release of Se(Ⅳ) by its physical and chemical properties and surface groups.

      • Changes of δ15N Values during Ammonia Volatilization from Different Upland Soils in China

        LI Miao, TI Chaopu, PENG Lingyun, TAO Limin, BAI Xiao, LI Chenglin, MENG Lei, YAN Xiaoyuan

        DOI: 10.11766/trxb202110190563

        Abstract:

        【Objective】Atmospheric ammonia (NH3) is an important precursor for the formation of PM2.5. Hence, identification and quantification of the sources of atmospheric NH3 are important for NH3 emission abatement and air pollution control. Farmland NH3 volatilization is one of the important sources of atmospheric NH3. The technology of natural abundance of nitrogen isotopes (δ15N) has been used to trace NH3 sources in recent years. Despite these advances, studies on the dynamic change of δ15N values from the whole process of NH3 volatilization from farmland soils are lacking. Moreover, NH3 volatilization from farmland soils is affected by different factors such as soil properties, pH, which can directly or indirectly influence the δ15N values of volatilized NH3 and may lead to uncertainties in sources traceability. Upland soil NH3 volatilization dominates total farmland NH3 volatilization in China. We selected four types of upland soil from different regions in China to study the δ15N values of NH3 volatilization from the whole volatilization process to clarify the changes of δ15N-NH3 values and their impacting factors.【Method】Urea was applied to four types of soils from Liaoning, Hebei, Henan and Tibet, and NH3 volatilization was studied in a 15-day indoor culture experiment by the sponge absorption method under controllable conditions. The δ15N value during the whole process of NH3 volatilization was measured by the chemical transformation method.【Result】Results showed that the values of δ15N during NH3 volatilization from Beipiao soil from Liaoning Province ranged from -26.14‰ to -5.57‰, with an average of -21.74±1.89‰. The variation range of δ15N values of Xinxiang soil (from Henan province) was from -31.92‰ to -26.31‰, with an average value of -29.31±1.72‰ while that of Tangshan soil (from Hebei province) and Linzhi soil (from Tibet) ranged from -24.41‰ to -3.11‰ with an average of 19.82±2.04‰, and from -29.17‰ to -2.20‰ with an average of -23.25±2.16‰, respectively. Overall, the δ15N values of the NH3 volatilization process in upland soils from different regions are different. During the whole process of soil NH3 volatilization, the δ15N-NH3 values of Xinxiang continued to increase, and the δ15N-NH3 values of Beipiao, Tangshan and Linzhi first decreased and then increased. Soil properties and NH3 volatilization rate are the main factors affecting the δ15N value.【Conclusion】Our results showed that soil pH, NH3 volatilization rate and cumulative NH3 loss were significantly negatively correlated with the δ15N-NH3 values. In addition, isotope fractionation also impacts the δ15N-NH3 values. The results of this study can provide better support for the quantitative traceability of atmospheric NH3.

      • Characteristics of Protist Community in Banana Rhizosphere Soil and Interactions between Protists and Pathogens of Fusarium wilt disease

        REN Xiangyu, LIU Manyi, SUN Mingze, YANG Jinming, WANG Beibei, LI Rong

        DOI: 10.11766/trxb202107140361

        Abstract:

        【Objective】As a serious banana disease and a significant limiting factor in banana production worldwide, banana Fusarium wilt disease is caused by the fungal pathogen Fusarium oxysporum f. sp. cubense race 4(FOC). The rhizosphere microbiome of plants is a key barrier that defends plant roots from an invasion of soil-borne pathogens. Most studies of the rhizosphere microbiome have focused on bacterial and fungal communities. However, as an important component of the rhizosphere microbiome, the rhizosphere protist community has been neglected in the regulation of microbiome and plant health. This study was conducted to explore the characteristics of the soil protist community in healthy and diseased plants and the interactions between protists and pathogens through field experiments of continuous cropping of bananas.【Method】In this paper, high-throughput Illumina MiSeq sequencing was applied to analyze the differences of soil protist community structure and composition among different treatments in field experiments.【Result】Results show that the relative importance of protists in predicting pathogenic Fusarium number was 47.19%, suggesting that protists might be the best predictor for pathogen number than culturable bacteria and fungi. The diversity and richness of the rhizosphere protist community decreased during plant growth and was lower in diseased plants. The composition and community structure of protists differed between healthy and diseased plants in rhizosphere soil. Also, the relative abundance of phagotrophic protists was highest compared to other functional groups in all soil samples, showing an increasing trend throughout plant development and enriched in diseased plants. Before the heading stage, the relative abundance of Bacillariophyta_X_unclassified, a phototrophic protist, was highest in healthy plants but decreased at a later stage. In healthy plants, the relative abundances of Group-Te and Cercomonas, phagotrophic protists, were higher at the heading stage. It was also observed that diseased plants showed a higher relative abundance of Pythium while phagotrophic protists, particularly cercozoan protists, had significant correlations with Fusarium than other protistan communities. Group-Te and Cercomonas, two Cercozoan taxa, were negatively linked with the pathogen. In contrast, pathogens in diseased plants were positively linked with Pythium, which was a plant pathogenic protist. 【Conclusion】Protists in the rhizosphere soil demonstrated a greater impact on pathogens. The community characteristics of protists in rhizosphere soil changed in the process of plant growth and differed between healthy and diseased plants. Particularly Group-Te and Cercomonas were negatively linked with the pathogen, which might have potential in the prevention and control of banana wilt disease. Future research should focus on (i) the isolation and purification of phagotrophic protists negatively related to pathogens, (ii) exploring the mechanism of phagotrophic protists and pathogens, and (iii) investigating the internal connection with other beneficial microorganisms in rhizosphere soil to improve the efficiency of controlling banana wilt.

      • Effects of Seawater Rice Rhizosphere Effect on Soil Ammonia-oxidizing Microorganisms in Coastal Saline-alkali Soil

        LI Gaoyang, HUANG Yongxiang, WU Weijian, CHEN Yijie, ZHANG Weijian, LUO Shuwen, LI Huijun, HUANG Fengcheng, LIN Zhong, ZHEN Zhen

        DOI: 10.11766/trxb202109170340

        Abstract:

        【Objective】The special environment of coastal saline-alkali land restricts the transformation and utilization of soil nitrogen. Microorganisms in saline-alkali paddy environment mediate ammonia oxidation in rice rhizosphere in a key process of soil nitrogen cycling. However, due to research blindness and outdated technology, the effect of seawater rice rhizosphere effect on the microbial community structure of ammonia oxidation in coastal saline-alkali soil is rarely reported. 【Method】In this study, the saline tolerant rice species ‘Haidao 86’ was used as the experimental material for the pot experiment. The pot experiment was conducted with low (2 g?kg-1) and high (6 g?kg-1) salt concentrations. Soil physicochemical properties and microbial biomass were measured and analyzed, and high-throughput sequencing of ammonia-oxidizing microorganisms was conducted to analyze the effects of different treatments of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) community structure in the rice rhizosphere.【Result】Results showed that after 70 days of rice growth, pH of rhizosphere soil decreased by 0.82 and 0.70, soil organic matter (SOM) content decreased by 6.41 g?kg-1 and 4.46 g?kg-1, humus (HU) content increased by 5.76 g?kg-1 and 4.45 g?kg-1, total nitrogen (TN) content decreased by 0.46 g?kg-1 and 0.37 g?kg-1 for low and high salt concentrations, respectively. Rice rhizosphere effect significantly increased soil microbial biomass carbon, microbial biomass nitrogen and microbial respiration intensity, reaching peak values on the 55th day of planting with 850.0 mg?kg-1, 72.2 mg?kg-1 and 231.9 mg?kg-1?d-1 for high salinity treatment and 546.1 mg?kg-1, 53.7 mg?kg-1 and 171.2 mg?kg-1?d-1 for low salinity treatment, respectively. The rhizosphere effect had no noticeable influence on the Chao1 index, Shannon index and Simpson index of AOA. At the genus level, the dominant bacteria of AOA were norank_c__environmental_samples_p__Crenarchaeota, unclassified_k__norank_d__Archaea, and Nitrososphaera. The rhizosphere effect of seawater rice significantly affected the richness, diversity and abundance of AOB in coastal saline-alkali soil. It can significantly increase the abundance of environmental_samples_f_Nitrosomonadaceae and Nitrosospira. Also, correlation analysis between the AOB community and soil environment showed that environmental_samples_f__Nitrosomonadaceae and Nitrosospira had a significant positive correlation with HU and a significant negative correlation with pH. 【Conclusion】The results of this study indicate that planting tolerant rice species can improve nutrient cycling in coastal saline-alkali land, and the rhizosphere effect of saline-alkali tolerant rice mainly affects the community structure of AOB in acidic soil.

      • Characteristics and Influencing Factors of the Catalytic Transformation of Ferrihydrite by the Structural Fe(II) in Reduced Montmorillonite

        LIAO Wenjuan, PENG Wei, WU Chong, NING Yaqi, WANG Shuai, CUI Haojie

        DOI: 10.11766/trxb202111020410

        Abstract:

        【Objective】Fe(II)-induced transformations of amorphous ferrihydrite to more crystalline iron oxide phases is a widely occurring geochemical process in soils under reduced conditions, and play an important role in regulating the biogeochemical processes of nutrient elements and pollutants. As one of the main species of Fe(II) in soils, Fe(II)-containing clay minerals are ubiquitous in soils under reduced conditions. However, the catalytic properties of structural Fe(II) in clay minerals for ferrihydrite transformation and its influencing factors are still not fully understood.【Method】In this study, the transformation of ferrihydrite induced by the structural Fe(II) in reduced montmorillonite (rSWy-2), which was produced by a chemical method, were investigated at neutral pH under anoxic conditions. Also, the influencing factors including types of cations and anions, organic matter, and As(III) on the transformation were studied. 【Result】The X-ray diffraction (XRD) and chemical extraction analyses results showed that the structural Fe(II) in rSWy-2 with low Fe content can catalyze the transformation from ferrihydrite to more crystalline lepidocrocite, and 83.3% of initial ferrihydrite converted to lepidocrocite after mixing reaction for 96 h. XRD, high-resolution transmission electron microscope (HRTEM), scanning transmission electron microscopy (STEM) and surface adsorbed Fe(II) content analyses showed that the processes of ferrihydrite transformation induced by the structural Fe(II) in rSWy-2 mainly included three stages: Firstly, positively charged ferrihydrite nanoparticles adsorption on negatively charged rSWy-2 surface through electrostatic interaction. Secondly, interfacial electron transfer from the structural Fe(II) in rSWy-2 to the adsorbed ferrihydrite and partly reducing Fe(III) to surface adsorbed Fe(II). Finally, the surface adsorbed Fe(II) catalyzed the transformation of ferrihydrite to more crystalline lepidocrocite phases. HRTEM analyses showed that the formed lepidocrocite phases presented nanoplates with a size range of 100~200 nm. XRD and chemical extraction analyses results showed that Na+ and Cl- ions in the mineral suspension had a weak effect on the catalyzed transformation from ferrihydrite to lepidocrocite phases by the structural Fe(II) in rSWy-2. In contrast, Ca2+, SO42-, organic matter, and As(III) all had obvious inhibition on the transformation due to their strong interactions with minerals. 【Conclusion】The structural Fe(II) in rSWy-2 could catalyze the transformation of ferrihydrite to lepidocrocite at neutral pH under anoxic conditions, and coexisting divalent cations and anions, As(III), and organic matter could inhibit the transformation reaction. The results provide a theoretical basis for further understanding the role of iron-bearing clay minerals in regulating abiotic transformations of iron oxides in soils under anaerobic reduction conditions.

      • Contributions and Influencing Factors of Soil Fauna to Litter Decomposition under Different Land-use Patterns

        yuanfang, DENG Chengjia, TANG Jing, SONG Lihong

        DOI: 10.11766/trxb202110090441

        Abstract:

        [Objective] Soil fauna play an important role in litter decomposition processes through activities such as burrowing and feeding. Besides the quality of litter, climate parameters have been identified as major factors affecting the role of soil fauna on litter decomposition. However, the contribution of soil fauna in litter decomposition and the role of climatic parameters under different land-use patterns are still not clear. [Method] In this paper, meta-analysis was used to quantify the effect sizes of soil fauna on litter decomposition rates. We established a meta-analysis database by collecting the results of 56 publications both in Chinese and English in China from papers published until May 31, 2021. The effect size of soil fauna on litter decomposition rates among three different land-use patterns (i.e., forest, grassland, and farmland), was further tested by a random-effects model. Correlations were tested between environmental factors - temperature, precipitation, litterbag size, latitude, and experimental duration – and the effect size of soil fauna on litter decomposition rates. [Result] Soil fauna increased litter decomposition rate by an average of 8.10%, reaching a significant level among different land-use patterns. Among the three different land-use patterns, the effect of soil fauna on litter decomposition rates was strongest in the farmland (12.36%). Environmental factors were closely correlated with the effect size of soil fauna on litter decomposition rates. [Conclusion] In the forest, effect size significantly increased with temperature, including the average temperature in January and July, and the mean annual temperature (P < 0.01). In grassland, however, the effect size of soil fauna decreased with temperature (P > 0.05). The effect size significantly increased with mean annual precipitation but significantly decreased with altitude (P < 0.01). Besides, with the increase of litterbag size and experimental duration, the effect size values of soil fauna on litter decomposition significantly increased and decreased, respectively.

      • Soil Texture Grading and Zoning for Tobacco Planting in Yuxi at 100 m Spatial Resolution

        XIE Xinqiao, LU Junping, TIAN Yutian, YANG Jizhou, LI Xiangwei, SUN Weixia, SONG Zhengshan, SHI Xuezheng

        DOI: 10.11766/trxb202109280526

        Abstract:

        【Objective】The development of soil texture grading and zoning is of practical significance for improving tobacco quality. 【Method】Based on the soil profile data recorded in the soil species records of Yunnan province (prefecture and county), combined with GIS technology and geostatistics, this study carried out a high-precision division of soil texture and quality for a tobacco plantation in Yuxi City. A spatial database of soil texture at 100 m spatial resolution level was built, and the quality grade of soil texture of the key soil factors for tobacco zoning was scientifically divided. 【Result】The results showed that the soil texture and quality suitable for tobacco planting in Yuxi varied greatly. According to soil texture and quality, the areas of grade I to grade V were 9.87%, 36.08%, 11.7%, 21.38% and 20.97%, respectively. The most suitable grade I soil for tobacco planting was mainly distributed in Eshan and Huaning counties, with an area of 26.2 km2 and 25.2 km2, respectively. Also, suitable second class soils were mainly distributed in Xinping, Yuanjiang and Jiangchuan, with an area of 87 km2, 58.6 km2 and 55.5 km2, respectively. There were obvious differences in soil texture and quality for tobacco plantation soils at different altitudes. The main suitable tobacco plantation area was at the altitudes of 1600 ~ 2000 m. 【Conclusion】The spatial distribution of soil texture at 100 m spatial resolution level in Yuxi was as detailed as village scale, which greatly improved the precision and practicability for tobacco plantation zoning. These results can provide a theoretical basis for high-quality tobacco production, long-term zoning and scientific management of soils.

      • Effects of Long-term Fertilization on Phosphorus Adsorption Characteristics of Fluvo-aquic Soils

        YANG Jiao, XIN Xiuli, ZHONG Xinyue, DING Shijie, ZHAGN Xianfeng, REN Guocui, ZHU Anning

        DOI: 10.11766/trxb202108060406

        Abstract:

        【Objective】The availability of soil phosphorus (P) usually limits the productivity of fluvo-aquic soil. In order to provide a scientific basis for improving P use effectivency and rational fertilization in fluvo-aquic soils, the adsorption characteristics of P and its relationship with soil properties under long-term fertilization were studied.【Method】We selected seven treatments: no fertilizer (CK), no P fertilizer (NK), no potassium fertilizer (NP), no nitrogen fertilizer (PK), mineral fertilizer NPK (NPK), half compost plus half mineral fertilizer NPK (1/2OM) and compost alone (OM) in a long-term fertilization experiment at Fengqiu, to determine soil properties and P adsorption capacity. The Langmuir and Freundlich equations were used to fit the isothermal adsorption curves. Furthermore, the maximum adsorption capacity (Qm), adsorption constant (K), maximum buffer capacity (MBC), P adsorption saturation (DPS), Freundlich adsorption constant (a) and adsorption index (b) were calculated. Correlation analysis and redundancy analysis (RDA) were used to explore the vital factors affecting the soil P adsorption characteristics.【Result】The results showed that P adsorption in fluvo-aquic soil fitted both the Langmuir (R2≥0.80) and Freundlich (R2≥0.89) isotherms. With the increase of P concentration in the equilibrium solution, P adsorption capacity rapidly increased at first and then slowly afterwards. Compared with CK and NK, Qm and MBC of NP, PK and NPK increased by 15.62%~23.60% and 2.94%~23.46%, respectively, however, K and MBC of 1/2OM and OM reduced by 39.60%~49.57% and 36.09%~56.15%, respectively. Correlation analysis and RDA results showed that organic matter (SOM), pH, free Al oxides (Ald) and C/P were the main factors affecting P adsorption characteristics of fluvo-aquic soil. In addition, the DPS of 1/2OM was 30.92% lower than that of OM.【Conclusion】Long-term combined NPK fertilizer with compost can increase the content of SOM, reduce P adsorption capacity and reduce the risk of P loss compared with OM.

      • Effects of Nitrogen Form and Phosphorus Fertilizer on Phosphorus-solubilizing Bacteria and Phosphatase of Maize Rhizosphere in Acidic Red Soil

        GUO Long, FENG Tongyu, XUE Zhuangzhuang, WANG Chao, SHEN Renfang

        DOI: 10.11766/trxb202108250454

        Abstract:

        【Objective】Low phosphorus (P) availability limits the increase in the productive capacity of acidic soils. The bacteria phoC and phoD genes encode acid and alkaline phosphatase (ACP and ALP), respectively, which mineralize organic phosphorus (P) to inorganic P, are affected differently under different fertilization regimes. However, the combined responses of phosphorus-solubilizing microorganisms (PSM) to fertilization strategies and the rhizosphere effect are still unclear.【Method】In this study, we evaluated the response of maize to the interaction of different nitrogen forms (ammonium nitrogen and nitrate nitrogen) and phosphate fertilizer levels. The phoC and phoD genes, separately coding for acid and alkaline phosphatase productions, were used as molecular markers to investigate the effects of fertilization strategies and rhizosphere effect on soil phosphatase activities and associated functional microbial communities in acidic soil.【Result】The rhizosphere effect significantly increased soil phosphatase activities in the rhizosphere. ALP activities in the rhizosphere under nitrate-nitrogen treatment were lower than in the corresponding ammonium nitrogen treatment. Also, the strength of the rhizosphere effect was greater than that of nitrogen forms and phosphate fertilizer levels. Nitrogen forms, phosphate fertilizer levels and rhizosphere effect all significantly affected the operational taxonomic units (OTU) number and Shannon index of phoD-harboring bacteria, but only nitrogen forms and rhizosphere effect affected the OTU number of phoC-harboring bacteria. Principal coordinate analysis (PCoA) and PERMANOVA analysis showed that the rhizosphere effect exhibited more influence on the phoC- and phoD-harboring bacterial community composition than nitrogen forms and phosphate fertilizer levels, with more effects on the phoD-harboring bacterial community. The stimulation of soil phosphatase activities in the rhizosphere was closely related to the increase in soil organic matter. Additionally, changes in the composition and structure of phoC-harboring bacterial community were mainly related to the changes in rhizosphere nutrients, while the changes of phoD-harboring bacterial community structure may be attributed to combined effects of root exudates and nutrient changes.【Conclusion】The rhizosphere showed more influence on soil phosphatase activities and associated functional bacterial communities than nitrogen forms and phosphate fertilizer levels in acidic soil. However, the strength of the effect strongly relied on the fertilization strategies.

      • Dewaterability of Frozen-melt Brackish Water and Its Soil Salt Leaching Efficiency Based on HYDRUS-1D

        WANG Ruiqi, LI Xianwen, ZHENG Na, JIANG Simin, CHEN Junying, YAN Baowen, HE Yujiang

        DOI: 10.11766/trxb202105250272

        Abstract:

        【Objective】Soil salinization is of growing concern in China since it severely restricts agricultural development and poses ecological and environmental risks in arid and semi-arid regions. High soil salinity causes deterioration of soil physical and chemical properties and inhabits plant growth. Given the wide distribution of brackish groundwater in arid and semi-arid regions, brackish irrigation is an effective approach to mitigate the shortage of freshwater resources. In addition, the naturally low air temperature in winter makes it possible to combine brackish irrigation and freeze-melt processes to enhance salt leaching and thus help reduce soil salinity. 【Method】 To reveal the dewaterability of frozen brackish water, the melting rates and temporal changes in water quality of ice blocks frozen from brackish water were compared under two air temperatures (10 ℃, 15 ℃) and four initial salinity gradients (freshwater, 0.5 g·L-1, 2 g·L-1, and 4 g·L-1). Furthermore, to evaluate the salt leaching efficiency through saline soil by melted brackish water, the HYDRUS-1D model was applied to simulate the one-dimensional soil water and salt transport patterns under two scenarios: direct infiltration using brackish water and infiltration using desalinized water melted from brackish ice frozen at different initial salinity gradients.【Result】 Our results show that: (1) The amount of melting water per unit time of brackish water ice body increased first and then decreased, and the melting rate was faster and peaked at higher value when the initial salinity was greater; (2) Freeze-melt could effectively desalinize brackish water by selectively discharging brine with great salinity at the early stage of melting, and the dewaterability was greater at lower initial salinity with an average dewaterability > 75 %; (3) The HYDRUS-1D simulations on saline soil illustrated a better leaching efficiency when infiltrated with water melted from frozen brackish ice than directly applying unfrozen brackish water, and the leaching effect of brackish ice meltwater was better at 10 ℃ than at 15 ℃.【Conclusion】 These findings proved the applicability and effectiveness of combining brackish groundwater with freeze-melt treatments, as a new water-saving and salt-controlling mode, to help mitigate freshwater shortage and reduce soil salinization risk in the arid and semi-arid of China.

      • Spatio-temporal Evolution Characteristics of Soil Potassium in Main Dry-farming Grain Arable Land of China

        LIU Kailou, DU Jiangxue, MA Changbao, Qu Xiaolin, HAN Tianfu, LIU Shujun, LI Yazhen, LI Dongchu, ZHANG Huimin

        DOI: 10.11766/trxb202109080399

        Abstract:

        【Objective】 Upland soil, as an important type of arable land in China, plays an extremely important role in national food security and stability. Since the reform and opening of China, there were many great changes in farmers"" fertilization patterns and planting habits because of soil testing formula fertilization, straw returning and fertilizer reduction to increase efficiency. However, there is still a lack of systematic research on the effects of these changes on the input of potassium (K) fertilizer and soil K in the main dry-farming grain of China. Therefore, the objective of this study was to evaluate the evolution characteristics of K input and fertility in major wheat and/or maize production regions of the whole country, which will clarify the present situation of K fertility and provide certain theoretical guidance for rational application of K fertilizer in different regions. 【Method】 This study was based on the National Cultivated Land Quality Monitoring database, which was from the Center of Cultivated Land Quality Monitoring and Protection, Ministry of Agricultural and Rural Affairs. Then, the K fertilizer input, soil available K (AK) and slowly available K (SAK) contents were analyzed in five regions of China, which included Northeast of China (NEC), North of China (NC), East of China (EC), Northwest of China (NWC), Southwest of China (SWC) during 1988-2007 and 2008-2018. Meanwhile, the effects of soil AK on SAK were also discussed. 【Result】 There was a relatively stable chemical K, straw K, and total K fertilizers (K2O) input in the whole country during 1988-2018, with 125 kg?hm-2?a-1, 148 kg?hm-2?a-1, and 273 kg?hm-2?a-1, respectively. There was no significant change for K input during 1988-2007 and 2008-2018. In different regions, it was observed that K input in NC and NEC regions was significantly higher than that in other regions. Compared with those of 1988-2007, the total K input in NEC, NC, EC, and SWC regions was increased during 2008-2018 by 4.22%-23.8%, while it was decreased slightly in the NWC region. The AK and SAK of the whole country were 139 mg?kg-1 and 665 mg?kg-1, respectively. Compared with 1988-2007, the AK and SAK during 2008-2018 increased by 15.1% and 6.72%, respectively. The order of soil AK in the different regions was higher in NWC and NEC regions (more than 150 mg?kg-1), lower for NC and EC regions (136~149 mg?kg-1), and lowest for SWC region (116 mg?kg-1). During 2008-2018, soil AK in NC, EC, NWC and SWC regions was increased more than during 1988-2007 by 15.7%, 17.7%, 4.16% and 34.5%, respectively. Also, the soil SAK was increased by 8.95%, 2.15%, 5.71% and 4.19%, respectively. In the main dry-farming food soils of the whole country, the relationship between soil AK and SAK could be fitted by a linear equation. With the increase in soil AK, the growth rate of soil SAK in 2008-2018 (14.2 mg? kg-1) was significantly higher than 1988-2007 (7.23 mg?kg-1). Meanwhile, the fitting equations among different regions in 1988-2018 also showed that the growth rate of soil SAK in NEC, EC and NWC regions was significantly higher than that in the NC region. 【Conclusion】 On the long-term monitoring platform of farmlands in China, compared with 1988-2007, the AK and SAK of main dry-farming grain soil were increased significantly during 2008-2018, and there was an increasing trend in most regions. Also, there was a significant linear relationship between soil AK and SAK. These results should provide a technical reference for the rapid estimation of SAK content even though there were differences in the fitting equations during different experimental periods and regions. Thus, it is recommended that different areas should accurately classify soil K supply capacity through AK and SAK by local conditions since it would establish the foundation for realizing the goal of storing K in the soil.

      • Research Progress on Microbial-Mediated Mitigation of Nitrous Oxide Emissions from Agricultural Soils

        SHEN Weishou, XIONG Ruonan, ZHANG Huanhuan, YANG Siqi

        DOI: 10.11766/trxb202106170315

        Abstract:

        Nitrous oxide (N2O), an important greenhouse gas, has a global warming potential of 265 times higher than that of an equivalent concentration of carbon dioxide. The N2O has a long atmospheric lifetime and does deplete the ozone layer in the stratosphere. Agricultural soil is an important source of N2O, which has a characteristic of diverse generation paths, multiple impact factors, and complicated regulation processes. Mitigation of N2O emissions from agricultural soils has long been the hotspot of research in this field. N2O-reducing bacteria harboring N2O reductase can reduce N2O to dinitrogen (N2), which is the only known sink of N2O consumption as a primary substrate in the biosphere. The direct use of microorganisms to decrease N2O emissions from agricultural soils is an emerging technology. We elaborated on the biological sources and sinks of N2O emissions from agricultural soils in detail, paying special emphasis on the screening and application strategies of microorganisms that can mitigate N2O emissions. There are three strategies for the direct use of microorganisms to decrease N2O emissions from agricultural soils: (1) application of the prepared microbial inoculum directly to the agricultural soil; (2) combination of the prepared microbial inoculum with fertilizers or other carriers before being applied to the soil; (3) construction of the microbial community with N2O mitigation effect, and then direct application to the soil or in combination with a carrier before being applied to the soil. We summarized two ecological mechanisms of microbial-mediated mitigation of N2O emissions from agricultural soils. One mechanism involved employing N2O-reducing bacteria containing nosZ gene to directly convert N2O to N2 in order to mitigate N2O emissions from agricultural soils. The other mechanism utilizes plant growth-promoting rhizobacteria to alter the community composition, abundance and activity of the N2O-reducing bacteria and indirectly mitigate N2O emissions from agricultural soils. We also discussed the environmental factors that affect the reduction of N2O to N2 by directly using microorganisms and the potential challenges. The biological process of reducing N2O to N2 is affected by many environmental factors, including the availability of NO3? and carbon sources, oxygen concentration, moisture content, temperature, pH and copper concentration. Among them, Cu availability and pH are some of the most important factors that determine the activity of N2OR. Several issues need to be addressed in future studies. For example, there are only a limited number of strains that have been screened with N2O mitigating effects. It remains unknown whether the inoculum colonizes roots or survive in the environment after the inoculation. The microbial ecological mechanisms are poorly understood; such as, how the inoculum achieve their beneficial effects in environments. Moreover, we lack effective technical means to regulate the inoculum to fully exploit their beneficial effects. Further, the methods to evaluate N2O mitigating effects also need to be improved. Finally, prospects on the application of microbial-mediated mitigation of N2O emissions from agricultural soils were suggested. The review provides an important technical reference for achieving the agricultural carbon neutrality strategic goal in China.

      • Spatiotemporal Variation of Fertility Quality of Chinese Paddy Soil Based on Fuzzy Method in Recent 30 Years

        HAN Tianfu, LIU Kailou, MA Changbao, WANG Huiying, QU Xiaolin, YU Zikun, XIE Jianhua, ZHANG Huimin

        DOI: 10.11766/trxb202107050343

        Abstract:

        【Objective】The spatiotemporal variation characteristics and driving factors of fertility quality of paddy soils in China were studied. 【Method】 Based on the long-term monitoring data (1988-2017) of the Ministry of Agriculture and Rural Affairs in the main rice areas in China, the fertility quality of paddy soil in the main rice areas was evaluated by the fuzzy mathematics (Fuzzy) method, and combined geo-statistics with machine learning.【Result】In the recent 30 years, the soil fertility index (SFI) of the rice area in China increased significantly (P < 0.05). From the prophase (1988-1999) to the interim (2000-2009) and from the interim to the recent (2010-2017), the national paddy field SFI increased by 6.9% and 17.7% on average, respectively. The characteristics of SFI varied in different time stages in the main rice regions. The rice regions in southwest China and the middle reaches of the Yangtze River showed a significant increasing trend of slow in the early period (from prophase to interim) and fast in the later period (from interim to recent) (P < 0.05). Also the rice fields in South China and the Yangtze River Delta showed a rising trend of fast in the early stage (from prophase to interim) and stable in the later stage (from interim to recent). There was a decreasing trend in the earlier period (from interim to recent) and increasing in the later period (from interim to recent) in the Northeast rice region. At the recent, the distribution of paddy SFI in China showed a trend of higher in the north and lower in the south, higher in the east and lower in the west. The area with SFI exceeding the national average (0.61) accounted for 50.2%. Compared with the SFI of the rice region in the interim, the SFI showed an overall upward trend in the recent. The increased area accounted for 69.3%. The relative importance of soil organic matter and total nitrogen to SFI change (19.4%-60.3%) was much higher than that of other indexes (0.1%-13.3%) in all rice areas in the prophase and interim (except the middle stage of the northeast rice region). The relative importance of soil Olsen-P, available potassium and soil pH (except the northeast rice region) increased in all rice regions, and the relative importance of soil Olsen-P content increased to the maximum in the middle reaches of the Yangtze River. However, the relative importance of soil total nitrogen and soil organic matter content was greater in all rice regions.【Conclusion】In conclusion, the spatiotemporal variation characteristics of soil fertility quality and the changes of key driving factors at different stages and in different rice regions should be comprehensively considered. The balanced fertilization measures should be optimized to prevent and control soil acidification and to improve the fertility quality of paddy soil.

      • Contributions of Various Forms of Nitrogen to Nitrogen Uptake by Maize in Red Soil with Different Fertilities

        ZOU Hongqin, LI Dejin, REN Keyu, WANG Boren, CAI Zejiang, XU Minggang, DUAN Yinghua

        DOI: 10.11766/trxb202108060408

        Abstract:

        【Objective】Soil nitrogen (N) is an important resource for N uptake by crops. The availability of soil N is dependent on soil fertility to a high extent, which in turn affects the absorption and utilization of N by crops. Understanding the various N forms in red soils with different fertility and their contribution to crop N uptake can provide a theoretical basis for clarifying the N cycle mechanism and cultivating high-yield and high-N efficiency soils.【Method】In May 2019, low-fertility, medium-fertility and high-fertility red soils were selected for the field micro-area experiments, and two treatments, no nitrogen fertilizer (N0) and conventional fertilization (N1) were set up. We determined the contents of soil mineral nitrogen (MN), fixed ammonium (FN), microbial biomass nitrogen (MBN) and soluble organic nitrogen (SON) before planting and after harvest of 2020 maize (the third crop of the experiment). The relationship model between each form of N and the quantity of N uptake was established through structural equation modeling (SEM). 【Result】The grain yield of high fertility soil under N0 treatment was about 4.6 times that of medium fertility soil. Under N1 treatment, the maize yield and biomass of high fertility soil had no significant difference with that of medium fertility soil. Meanwhile the N uptake of high fertility soil was significantly higher than that of medium fertility soil. Compared with before planting, the FN content in the medium-fertility soil after harvest was significantly increased by 63% under N0 treatment. The FN of low and high fertility soil increased by 47% and 11%, respectively, while the contents of MN, MBN and SON in the soil were reduced. The MN content of the soils was decreased by between 0.4-4.0 mg?kg-1. MBN was decreased by 18%-44% and there was no significant difference in soil fertility. Also, the SON was decreased by 55%-84%. Under N1 treatment, the content of MN was decreased by 22~38 mg?kg-1 and the content of MBN was reduced by 32%-72%. The SON was reduced by 99 mg?kg-1 in high-fertility soil, which was 2.0 times higher than medium-fertility soil and 9.3 times higher than low-fertility soil. The correlation analysis results revealed a significant positive correlation between the amount of N uptake by the aboveground biomass and the decrement of MBN, SON and NH4+-N. The structural equation model results further showed that the content of SON and NH4+-N directly affected the amount of N uptake, while MBN indirectly affected the N uptake by maize by changing SON and MN.【Conclusion】SON and NH4+-N can directly regulate the maize N uptake. The MBN and FN indirectly affect maize N uptake through the MN and SON. In the future, it is crucial to strengthen the research on the mechanism of soil N form transformation to promote red soil fertility and high-efficiency utilization of N.

      • Phosphorus Level Regulates the Interaction Between Endophytic Fungus Phomopsis liquidambaris and Rice

        CHEN Man, ZHANG Yang, BAI Yanan, DAI Chuanchao

        DOI: 10.11766/trxb202108030397

        Abstract:

        Objective】The interaction between endophytic fungi and plants is affected by many factors, among which the content of phosphorus in soil plays a key role in regulating the interaction between them. However, it is not clear whether and how phosphorus fertilizer in the environment affects the interaction between endophytic fungi and plants.【Method】In this study, the symbiont of Phomopsis liquidambaris (B3) and rice(Oryza sativa L.)was used as the experimental model. Three different phosphorus levels, i.e., low phosphorus (LP), medium phosphorus (MP), high phosphorus (HP) , uninoculated endophytes treatment (E-), and inoculation endophytes treatment (E+) were designed in this experiment. Physiological indexes of rice and B3 colonization were detected under different phosphorus levels to explore how phosphorus regulates the interaction between B3 and rice in the outdoor experiment and greenhouse experiment. 【Results】In the outdoor experiment, B3 significantly (i) increased the phosphorus uptake ability of rice, (ii) promoted rice growth in the whole growth period and the formation of rice grain in the mature stage, and (iii) increased the rice yield by 7.05% under LP treatment. When under MP and HP treatments, the effect of B3 was weakened. In the greenhouse experiment, under LP treatment, compared with the uninoculated treatment, the root/shoot ratio of rice inoculated with B3 increased by 22.48%, and resulted in an enhanced phosphorus uptake ability of rice by 39.98%. There was a significant enhancement of photosynthesis in rice and the accumulation of carbon sources such as sucrose, glucose and fructose in rice roots. However, the colonization of B3 was significantly limited under this condition. Also, consistent with this result, the biomass of B3 cultured in the LP medium was significantly lower than that in MP and HP mediums, which meant that B3 would be significantly affected by the phosphorus concentration. In the MP and HP treatments, B3 had high colonization in rice roots, but had little effect on rice growth. 【Concusion】Phosphorus concentration affects the symbiotic relationship between B3 and rice. In LP treatment, B3 colonization was low in rice roots, but it significantly promoted plant growth. In MP and HP treatments, B3 had high colonization rates in rice roots but with no significant effect on rice growth. Understanding the influence of phosphorus fertilizer on the interaction between endophytic fungi and plants will be helpful to improve the utilization efficiency of phosphorus fertilizer and microbial resources, which will provide a new path for the sustainable development of agriculture.

      • Acidification Resistance of Tobacco-planting Soils Derived from Different Parent Materials in Wuling Qinba District, China

        SHI Renyong, WANG Changjun, YAN Jing, LAI Hongwei, CHEN Zhenguo, LI Decheng, XU Renkou, SUN Jingguo

        DOI: 10.11766/trxb202107010339

        Abstract:

        【Objective】 This study aimed to investigate the effects of parent materials and initial soil pH on the resistance of soils to acidification. 【Method】 Twelve soil samples derived from different parent materials under tobacco-cultivation were collected from Wuling Qinba District, China. The pH buffering capacity (pHBC) of the different soil samples was determined by acid-base titration in the pH range 4.0 to 7.0. Additionally, the changes of soil pH, soluble Al and exchangeable Al following acid input were investigated through simulated acidification with HNO3. 【Result】 The results showed that soil pHBC was significantly affected by parent materials and initial soil pH. Due to the depletion of buffering substances in soils by acidification, the pHBC of weakly acidic yellow-brown soils and yellow soils (11.79-45.15 mmol?pH-1?kg-1) was lower than that of neutral yellow-brown soils and yellow soils (23.74-141.53 mmol?pH-1?kg-1). Therefore, the decrease in soil pH and increase in soil active Al in neutral yellow-brown and yellow soils were slow during the simulated acidification, indicating a weak acidification potential. Among the neutral yellow-brown soils and yellow soils, the soil pHBC increased with an increase in carbonate content in soils. The soils derived from limestone and carbonate parent materials reserved more carbonate (21.14 and 1.18 g?kg-1), which led to a higher pHBC than soils derived from quartzite and siliceous parents. However, the opposite tendencies were observed in the weak acid yellow-brown soils and yellow soils. In weak acid soils, the exchangeable base cations played the major pH buffering role due to the exhaustion of carbonate. Compared with the soils derived from limestone and carbonate parents, soils derived from quartzite and siliceous parents contained more clay and organic matter, which provided more H+ exchangeable sites and was thus beneficial to buffer exogenous acid and slow down the activation of soil aluminum during acidification. Among the 12 tested soils, the acidic yellow-brown soil derived from pelite was extremely sensitive to exogenous acids due to the lowest pHBC (11.79 mmol?pH-1?kg-1). When 6 mmol?L-1 HNO3 was added, the pH of the acidic yellow-brown soil derived from pelite was lower than that of the acid yellow-brown soils derived from carbonate parents and siliceous parents (by 0.74 and 1.10 pH units, respectively). Correspondingly, the soluble Al and exchangeable Al in the acid yellow-brown soil derived from pelite were significantly higher than those in the acid yellow-brown soils derived from carbonate parents and siliceous parents. 【Conclusion】 The acid yellow-brown soil derived from pelite presented the highest potential acidification risk. Thus, it is necessary to pay more attention to the acidification trend of soils derived from pelite and improve the resistance of these soils to acidification through the application of organic fertilizer. These findings provide significant guidelines for the management of soil acidification during continuous tobacco cultivation in the Wuling Qinba region, China.

      • Human Bioavailability and Health Risk Assessment of Heavy Metals in Soils from a Mining Area of Southwest China

        BAO Xinchen, MA Jiaoyang, XU Wumei, WANG Haoji, WANG Chengchen, XIANG Ping

        DOI: 10.11766/trxb202107200287

        Abstract:

        【Objective】Ingestion of soil is a pathway of human exposure to several environmental contaminants, including several heavy metals. Risk assessment of soils has typically been performed on total concentrations of target heavy metals. However, it may overestimate the potential adverse effects. To refine exposure risk, bioaccessibility and bioavailability measurements have been employed in many studies. Bioaccessibility tests are used to measure the bioaccessible fractions of contaminants in soils while bioavailability evaluates the fraction of heavy metals that reach the systemic circulation. These tests are both considered accurate approaches to evaluate the potential health risk of contaminants. However, there are few studies on the health risk assessment of heavy metals from mining soils via bioavailability. 【Method】In this study, five soil samples from the mining area of Wenshan, Yunnan Province were collected and the levels of Cd, Pb, Zn and Cu were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The bioaccessibility of Cd, Pb, Zn and Cu was detected using in vitro digestion method (SBRC), and the relative bioavailability (RBA) of Cd was determined by BALB/c mice models. The health risks of the four heavy metals in mining soils were assessed based on total, bioaccessible, and bioavailable data, respectively.【Result】The results showed that Cd pollution in this study area was serious, with the content being 2.06 mg?kg?1, which was 9.36 folds higher than the limit of soil background value in Yunnan. The bioaccessibility of Cd, Pb, Zn and Cu in the gastric phase was 24.29%-50.55%, 7.68%-17.87%, 24.61%-32.18%, 7.75%-37.87%, respectively, while in intestinal phase, they were 22.78%-44.32%, 1.64%-5.22%, 14.10%-28.11%, 8.51%-31.49%, respectively. As evident, the bioaccessibility of Cd was the highest among the four heavy metals. The RBA of Cd measured in vivo was 1.31%-48.39% in the liver, 2.83%-8.58% in the kidney, and 4.60%-50.95% in the liver and kidney. Compared with a single endpoint, Cd-RBA in the liver and kidney provided better repeatability and were ideal target organs for the determination of Cd-RBA. In vivo- in vitro correlation showed that the bioavailability of Cd determined by SBRC had a poor potential to predict Cd-RBA in contaminated soils from the mining area in China. Health risk assessment of the mining soil based on the target heavy metals, bioaccessibility and bioavailability revealed that the assessment using the total heavy metals had greater human health risk, while the data based on bioaccessibility and bioavailability showed a significantly reduced risk. 【Conclusion】The health risks assessment based on the total heavy metals in soil may be overestimated, and the establishment of a new method based on the bioavailability data will be more accurate. Our results provide a scientific basis for the health risk assessment of contaminated soils in China.

      • Mechanisms of Diminishing Capacity for Mitigating Nitrous Oxide Emissions by Field-aged Biochar in the Rice-wheat Rotation Ecosystem

        ZHU Shuangge, ZHANG Qianqian, XU Xintong, BI Ruiyu, SONG Yanfeng, XIONG Zhengqin

        DOI: 10.11766/trxb202108250452

        Abstract:

        [Objectives] Biochar is an important soil amendment material, as it plays an increasingly prominent role in carbon sequestration and greenhouse gases mitigations, especially in nitrous oxide (N2O) mitigation. To investigate the effects and the mechanisms of the biochar aging process on soil N2O emissions under a rice-wheat rotation system, an in situ field experiment was conducted. [Methods] Five treatments were established as follows: CK (without urea and biochar), N (urea), NB0y (urea with fresh biochar), NB2y (urea with 2-year aged biochar) and NB5y (urea with 5-year aged biochar). Soil N2O emission dynamics were monitored during rice and wheat annual rotation. Also, soil physicochemical characteristics and the abundance of relevant microbial functional genes during the N2O production process were determined after rice and wheat harvest. [Results] Biochar treatment significantly reduced the cumulative N2O emissions by 32.4% - 54.0%, with the reduction capacity following NB0y> NB2y> NB5y. Compared with the N treatment, NB0y, NB2y and NB5ytreatment significantly increased soil pH by 0.6 -1.2 units, soil NO3--N content by 1.7% - 31.3%, and soil organic carbon (SOC) content by 21.4% - 58.6%. Nevertheless, the ability of biochar to improve soil pH was decreased with aging. Also, NB0y, NB2y and NB5ytreatments significantly increased the abundance of nosZ gene by 54.9% -249.4%, and the soil (nirS+nirK)/nosZ ratio increased with the biochar age. Meanwhile, the cumulative N2O emissions showed a significant negative correlation with soil pH, and a positive correlation with NO3--N content and amoA-AOB gene abundance. [Conclusions] In summary, both fresh and aged biochar can significantly improve soil physical and chemical properties and decrease soil N2O emissions, but the effect of fresh biochar was better than that of aged biochar. The mitigation capacity of aged biochar decreased mainly due to the increase of soil NO3--N content and (nirS+nirK)/nosZ ratio.

      • Seasonal Variations in Methane Production Potential and Methanogenic Pathway in a Permanently Flooded Rice Field

        ZHU Xiaoli, HUANG Qiong, SONG Kaifu, MA Jing, ZHANG Guangbin, XU Hua

        DOI: 10.11766/trxb202107050347

        Abstract:

        [Objective] The mitigation of methane (CH4) emission has long been the focus of governments and researchers worldwide. Rice fields are an important source of CH4 emission, and CH4 production is the precondition of CH4 emission. It is mainly produced by acetate fermentation and CO2/H2 reduction. Substantial CH4 emissions are observed from the permanently flooded rice fields, thus leaving a high mitigation potential of emission. However, reports on the seasonal variation of the methanogenic pathway in these rice fields are limited. [Method] Fresh soil samples from four rice growth stages (tillering stage, booting stage, heading stage, and maturity stage) were collected from a permanently flooded rice field in Ziyang City, Sichuan Province, China. The CH4 production potential (MPP) was observed through anaerobic incubation experiments. Both stable carbon isotope technique and methyl fluoride (CH3F, 2%) inhibition method were used to quantify the carbon isotopic fractionation factor for the conversion of CO2 to CH4 (α (CO2/CH4)), as well as to quantitatively estimate the relative contribution of acetate-dependent methanogenesis (? acetate). [Result] The addition of CH3F significantly decreased the CH4 production, and the MPP reached the highest value at the maturity stage, ranging from 3.22 to 12.71 μg·g-1·d-1. The δ13C-value of produced CH4 (δ13CH4) varied in the range -66.83‰ ~ -59.62‰, which was much more positive than that of produced CH4 with CH3F addition (-90.83‰ ~ -82.26‰). The α (CO2/CH4) reached its maximum and minimum values at tillering and booting stages, respectively, which was between 1.064 and 1.076. The ? acetate (30% ~ 61%) decreased sharply from 54% ~ 61% at the tillering stage to 30% ~ 35% at the booting stage and then increased to 54% ~ 61% at the maturity stage. Further analysis showed that the seasonal variation of MPP was positively correlated with the variation of soil dissolved organic carbon (DOC) content, and the seasonal variation of ? acetate was significantly related to variations of acetate content. [Conclusion] Distinct seasonal variations were observed in both MPP and methanogenic pathways of the permanently flooded rice fields, which was mainly affected by soil DOC content and acetate content, respectively.

      • Community assembly and functional potential of bacterial habitat generalists and specialists in typical paddy soils

        LIU Hongtao, HU Tianlong, WANG Hui, ZHANG Yanhui, GUO Shiwei, XIE Zubin

        DOI: 10.11766/trxb202105310284

        Abstract:

        Great differences exist in the utilization of carbon and nutrients between habitat generalists and specialists, which play unique roles in the cycle of soil energy and nutrients. At present, the research on farmland microorganisms mainly focuses on the whole bacteria, fungi, archaea or other functional communities, and the understanding of habitat generalists and specialists in farmland ecosystems is still lacking. Therefore, this study was designed to explore the community structure, assembly mechanism and possible functions of habitat generalists and specialists in typical paddy soils in eastern and southwestern China. Sixteen surface soil samples (0~20cm) were collected from the eastern area (Anhui, Jiangsu, Shanghai) and southwestern area (Yunnan and Guizhou) of China according to the data of the second soil survey, and their physico-chemical properties and next generation high-throughput sequencing were analyzed. The results showed that 3.28% of all OTUs were classified as habitat generalists while 9.07% as habitat specialists. There were significant differences in species composition between habitat generalists and specialists. At the level of phylum, the proportions of habitat specialists in Chloroflexi, Actinobacteria, Nitrospirae, Firmicutes and Planctomycetes were higher than those of habitat generalists. The analysis of the community assembly process based on the β diversity null model showed that habitat generalists and specialists were dominated by deterministic process. Compared with habitat specialists, habitat generalists were more affected by the stochastic process. The environmental factors driving the community structure variation of habitat generalists and specialists were different. pH, mean annual precipitation, clay content and total nitrogen were the main factors driving the community structure variation of habitat generalists, while the community structure variation of habitat specialists was dominated by pH and clay content. By analyzing the co-occurrence network and robustness of habitat generalists and specialists, it was found that the habitat specialists’ network had more connections, more complexed structure and stronger robustness. The functional prediction by FAPROTAX showed that biological nitrogen fixation mainly existed in habitat generalists. Information derived from the community structure, environmental driving factors, assembly process, co-occurrence network characteristics and related functions of nitrogen metabolism of habitat generalists and specialists, provides a theoretical basis for the evolution and regulation of bacterial communities in paddy fields.

      • Effects of Drying and Oxidation Stage on the Forms and Availability of Cd and As in the Soil-rice System

        ZHANG Yuting, ZHU Qihong, HUANG Daoyou, TIAN Yingbing, XU Chao, ZHU Hanhua, HE Lei, WANG Wei, ZHANG Quan

        DOI: 10.11766/trxb202105190264

        Abstract:

        【Objective】The chemical behavior of cadmium (Cd) and arsenic (As) in paddy soils is opposite to the change in biological efficiency. This presents serious challenges to the simultaneous control of Cd and As pollution in rice. Previous studies have found that continuous flooding of Cd polluted fields can reduce the bioavailability of Cd while reducing soil water content can mitigate the bioavailability of As. However, the forms and availability of Cd and As in the soil-rice system under the process of drying (oxidation) remain unclear. 【Method】In this study, continuous sampling during the process of drying (days 0, 3, 5, and 7 of the drying process) under tillering period of rice in a pot experiment was carried out. At the same time the soil samples were analyzed for pH, Eh, soluble organic carbon, available Cd and As, and the different forms of Cd and As. Also, the plant samples were analyzed for Fe plaque in the rice roots and Cd and As concentration in the rice tissues. 【Result】 The results showed that: during the process of drying, the Cd concentration in all parts of rice tissues increased with a reduction in water content, and the Cd concentrations in roots and shoots were increased by 109% and 183%, respectively, under the second drying stage (drying for 5 days) compared with the control treatment (P < 0.05). The concentration of As in rice roots decreased firstly and then increased with the reduction of water content. Compared with the control treatment, the concentration of As in rice roots was decreased by 41.96 mg·kg-1 (P < 0.05). Also, the shoot As concentration was decreased by 12% and 18%, respectively, under the second and third stages of drying (drying for 5 and 7 days) (P < 0.05). The Cd, As and Fe concentrations in the Fe plaque increased by 96%, 16% and 16%, respectively (P < 0.05). With the decrease of soil water content, soil Eh, soil soluble organic carbon, and soil available Cd extracted by DTPA were increased, but soil pH, soil available As, and soil available Fe extracted by DTPA were decreased. In addition, reducing soil water content promoted the transformation of residual Cd to acid extractable and reducible Cd, resulting in the increase of oxidizable As concentration. It was also observed that when the soil moisture content was 33.6%, the bioavailable Cd and As concentration remained relatively low. 【Conclusion】Reasonable water management practices can reduce the bioavailability of Cd and As in soil. This is due to the changing soil Eh, pH, soluble organic carbon and available Fe, and the promotion of adsorption and fixation of Cd and As by the Fe plaque. However, it is worth noting that while exploring water management methods to reduce the bioavailability of Cd and As, the growth and development of rice cannot be ignored. Our study contributes to the wealth of knowledge aimed at improving the remediation of Cd and As contaminated soils.

      • Study of the Water Infiltration Processes using ERT and TDR in Layered Soils

        LIN Qing, XU Shaohui

        DOI: 10.11766/trxb202104280227

        Abstract:

        【Objective】Soil water is the link between surface water and groundwater,and the carrier of solute transport in soil, which plays a key role in the Soil-Plant-Atmosphere Continuum (SPAC) system. The movement of soil water is a very complex process, especially in the layered structure. Heterogeneity of texture and pore of layered soil changes hydraulic characteristics at the interface of the soil layer, and thus the soil water movement and solute transport differ significantly from that in homogeneous soil.【Method】To fully understand the process of soil water movement, infiltration was evaluated using electrical resistivity tomography (ERT) in soil with a stratified profile. A field infiltration test was performed on an 8.7-m-long transect and successive measurements using ERT allowed determining resistivity changes as infiltration progressed. In the meantime, the soil water content was measured by time domain reflectometry (TDR) at the point scale, and the quantitative relationship was established between resistivity and water content. In addition, the soil water contents derived by ERT were validated with the soil water content derived by the drying method. 【Result】Results showed that the Multi-electrode resistivity method can fairly monitor the process of soil water movement, identify the depth of water infiltration, 90 cm in our study, and quantitatively retrieve the profile water content. The movement of soil water is mainly vertical downward with a weak horizontal flow. A good correlation between resistivity and soil moisture measurements revealed the capability of resistivity measurements to infer soil moisture spatial and temporal variability with root mean square error (RMSE) equal to 0.042 cm3·cm-3 for loam and 0.041 cm3·cm-3 for clay loam. However, when the soil water content was lower than 0.15 cm3 cm-3, the electrical resistivity changed greatly with the increase in water content, while the soil water content was higher, the resistivity did not change significantly with water content. When the soil water reached the interface (~30 cm) between loam and clay loam, the soil water did not immediately move to the lower layer. According to the established relationship between resistivity and water content, it is estimated that at the soil interface, when the mass moisture content reached 0.136 g·g-1 at the upper layer of the soil, the water infiltrated the lower layer. Unexpectedly, abnormally increased resistivity appeared under the area of the soil water infiltration, which was presumably caused by the significant difference in resistivity of soil adjacent layers during the infiltration process. 【Conclusion】 In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out without disturbing the soil. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in the field. Also, this study provides a new method for quantitative analysis of the movement of soil water at a layered interface.

      • Influence of Land Use Changes on Evolution of Different K Forms in Purple Paddy Soils

        LI Xiuzhi, HU Conyue, YANG Fan, HAN Guangzhong

        DOI: 10.11766/trxb202106290334

        Abstract:

        【Objective】Significant changes have recently taken place in the agricultural planting structure of the purple paddy soil area. These changes have profoundly affected the form and dynamic balance of soil potassium. Thus, understanding the impact of land-use changes on the evolution characteristics of different forms of potassium in purple paddy soil is of great significance to regional potassium management and environmental protection. 【Method】In this paper, we analyzed the dynamic characteristics and influencing factors of different forms of potassium in the purple paddy soil after abandonment, dry farming and conversion to fish ponds, using the time series method. 【Result】The results showed that abandonment and dry farming reduced the water-soluble potassium content of purple paddy soil, and conversion to fish ponds increased the water-soluble potassium content of purple paddy soil. Abandonment, dry farming and conversion to fish ponds could all increase the exchangeable potassium and non-exchangeable potassium content of purple paddy soil. Both the increasing magnitude and rate are highest for dry farming, intermediate for abandonment, and smallest for fish farming. 【Conclusion】In the purple paddy soil, potassium in different forms reached a general balance after 5 years of fish farming or 12 years after abandonment. However, after 20 years of dry farming, the different forms of potassium in the soil did not reach a general balance. The results also showed that the release of mineral potassium in purple paddy soil was relatively fast in the natural state. After the land-use changes, there were complex connections between the occurrence and dynamic balance of purple paddy soil, the loss of soil organic matter, and the transformation of soil clay minerals, which needs further research.

      • Responses of Soil Carbon Pool of Abandoned Grassland on the Loess Plateau to Two-years Warming and Increased Precipitation

        WANG Xing, ZHONG Zekun, WANG Jiayi, JIAN Junnan, YANG Gaihe, REN Chengjie, HAN Xinhui

        DOI: 10.11766/trxb202106120307

        Abstract:

        【Objective】Global climate change has had a huge impact on the carbon pool of terrestrial ecosystems, and the changes in average temperature and precipitation patterns pose severe challenges to the management of terrestrial carbon pools. This is especially serious in the Loess Plateau where the ecological environment is fragile. Therefore, understanding the changes of different fractions of soil organic carbon pool and the stability of this carbon pool under the background of the warming and humid climate of the Loess Plateau is of great significance. This will be of importance in the sustainable development of the carbon pool in fragile ecological areas and the evaluation of regional ecological benefits.【 Method】In this study, natural abandoned grassland in the loess hilly region was taken as the research object. Soil warming and increased precipitation were artificially simulated and the changes in vegetation community, soil carbon fractions content and distribution, carbon pool stability index under warming (W), precipitation (P50%) and their interactions (WP50%) were analyzed. 【Result】The results showed that: (1) P50% significantly increased the vegetation Gleason richness index, W and WP50% significantly reduced the Gleason richness index(P < 0.05)and the leaf organic carbon content under the WP50% was significantly higher than the control treatment. Both P50% and WP50% treatments reduced the Shannon-wiener diversity index and pielou evenness index. (2) Soil organic carbon (SOC), acid hydrolyzable organic carbon (AHC), easily oxidizable carbon(EOC), dissolved organic carbon(DOC)content and their distribution ratio of the two sampling years under P50% were significantly higher than the control treatment. Also, warming based on P50% can further increase soil EOC, microbial biomass carbon(MBC)content and distribution ratio. However, only the soil MBC showed a significant difference compared with the control under W treatment. Recalcitrant organic carbon (ROC) presents an opposite trend to AHC. The correlation analysis showed that there was a significant correlation between soil total organic carbon and each active carbon fractions(P < 0.05). (3) The soil carbon pool activity (CA), carbon pool activity index (CAI), and carbon pool management index (CPMI) under WP50% treatment were higher than other treatments. The sensitivity index of AHC and MBC was relatively high under the treatment of climate change.【Conclusion】In summary, the total organic carbon, the content and distribution ratio of active fractions of organic carbon, and the stability of the carbon pool in abandoned grassland of the loess-hilly area will be significantly improved under background warming and humid climate. This will contribute to the healthy development of the carbon pool. From a sensitivity point of view, AHC and MBC can be used as early important indicators of changes in soil organic carbon under warm and humid climates in the future. This study provides a theoretical and scientific basis for research on climate change and carbon pool management in fragile ecological areas.

      • Effects of Key-stone Microbe Based on Co-occurrence Networks on Wheat Yield in the Soils with Straw Returning

        QIU Lili, LI Dandan, ZHANG Jiabao, ZHAO Bingzi ☨

        DOI: 10.11766/trxb202107200372

        Abstract:

        【Objective】The mechanism of the inconsistent effects of straw application on crop yield is still unclear, and the main reason may be related to the insufficient understanding of the effects of straw application on soil microbial community composition and its abundance changes on crop yield.【Method】A pot experiment to study the growth of wheat was carried out using red and yellow-cinnamon soils. Three levels of straw application were set for each soil, namely 0, 10 and 30 g·kg-1 soil (S0, S10, S30). Based on bacterial-fungal co-occurrence networks, the Path analysis model was used to evaluate the contribution of microbial ecological clusters, enzyme activities and chemical properties to wheat yield.【Result】The results showed that although the content of available nutrients, soluble organic carbon, microbial biomass carbon and enzyme activities (amylase, invertase, polyphenol oxidase, urease, acid phosphatase, dehydrogenase) increased significantly in both soils, the wheat yield increased with the increase in straw dosage in the red soil but decreased in yellow-cinnamon soil. Compared with S0, S10 and S30 treatments increased wheat grain yield and above-ground biomass by 33%~44% and by 73%~85% in the red soil; and decreased wheat grain yield and above-ground biomass by 22%~25% and by 55% in the yellow-cinnamon soil, respectively. The abundance of two key ecological clusters within the bacterial-fungal co-occurrence network, enzyme activities and soil chemical properties had positive effects on wheat yield in red soil while the abundance of two key ecological clusters had a larger positive effect on wheat yield in yellow-cinnamon soil. The straw application significantly increased the abundance of Aspergillus, a key microorganism positively correlated with wheat yield in red soil, while significantly decreased the abundance of Bacillus, Burkholderia, and Basidiobolus, which were positively correlated with wheat yield in yellow-cinnamon soil.【Conclusion】The combined effects of straw application, an increase in key microbial abundance, enzyme activities, and improvement of soil chemical properties was responsible for improving wheat yield in the red soil. In the yellow-cinnamon soil, the decrease in wheat yield was mainly related to lower key microbial abundance, whose effect was superior to the potential positive effects of improved soil chemical properties and enzyme activities. These results suggest that the change in the abundance of key microorganisms has an important influence on the variation of crop yield after straw returning.

      • Research Progress on the Microstructure and Constituents of Fe-Mn Nodules in Soil

        WANG Yi, HUANG Laiming

        DOI: 10.11766/trxb202107130360

        Abstract:

        Ferromanganese concretions (or Fe-Mn nodules), as a specific type of soil neoformations, are formed during pedogenic processes. The structure of concentric rings in soil Fe-Mn nodules can be used to reconstruct paleoclimatic conditions and soil-forming environments. The constituents of soil Fe-Mn nodules can provide nutrients and energy for microbial metabolism that in turn affect the transformation, fixation and mobilization of soil nutrients and heavy metals. This article reviewed the research progresses on soil Fe-Mn nodules during the past several decades, including (i) the formation mechanism and process of Fe-Mn nodules and the associated influencing factors; (ii) differences in the microstructure and constituents of Fe-Mn nodules in different regions; and (iii) effects of Fe-Mn nodules on nutrient transformation and heavy metal sorption. Future research priorities include (a) study of the formation rates and environmental thresholds of Fe-Mn nodules during different stages of soil development; (b) establishment of the evolution models of Fe-Mn nodules in different soil-forming environments; and (c) elucidation of the mechanisms of stabilization and release of soil nutrients and heavy metals by Fe-Mn nodules. This will facilitate understanding of the pedogenic processes and elemental biogeochemical cycling in the Earth’s Critical Zone and provide a basis for quantitative evaluation of soil quality and function under changing environments.

About

Supervisor: Chinese Academy of Sciences

Sponsor:Soil Science Society of China

Editor-in-Chief:Xu Renkou

Address:71 East Beijing Road, Nanjing 210008, P. R. China

Zip Code:210008

Phone:+86-25-86881237

Email:actapedo@issas.ac.cn

ISSN:0564-3929

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