Abstract:Long-term archived soil samples, as an important part of the foundational support of national science and technology in China, is of great value to the study of long-term changes in soil and environment and the sharing of samples and data. In recent years, with the continuous increase of investment in agriculture and eco-environmental science and technology in China, soil surveys are more needed and the accumulation of soil samples is accelerating significantly. Thus, there is an urgent need for establishing the relevant standards and specifications for the long-term storage of soil samples. Based on the national standard "Soil quality Guidance on long and short term storage of soil samples (GB/T 32722-2016)", and combined with the experience constructing a distributed long-term soil archiving system in CERN during the 13th Five-Year Plan in China, a soil sample storage management strategy, the standards for soil sample archiving conditions and the information management system were introduced in detail in the paper. The system will help provide references for the long-term standardized storage of soil samples and the construction of soil samples archiving system for the Third Nationwide Soil Condition Census.

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.

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.

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.

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.

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.

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 (N_100%, pure nitrogen application of 180 kg·hm^–2), 1/6(N_1/6), 1/3(N_1/3), 1/2(N_1/2), and zero (N₀) nitrogen application rates.Result The peanut yield and plant nitrogen uptake of N_1/2 and N_1/6 treatments were insignificantly lower than those of the N_100% treatment (P > 0.05). Besides, N_1/6 and N_1/2 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). N_1/6, N_1/3, N_1/2, 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 N_100% treatment (P < 0.05). Also, N_1/3, N_1/2, and N₀ treatments reduced the average TN concentration in the leakage compared to the N_100% treatment. However, the average increase in TN leakage concentration in the N_1/6 treatment was not significantly different from that of the N_100% 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.

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(BD_1.1), 1.3(BD_1.3), 1.5(BD_1.5) and 1.7(BD_1.7) 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 BD_1.3, BD_1.5 and BD_1.7 compared with BD_1.1. In relative to BD_1.1, the increase of compactness decreased macro-porosity by 19.0%, 65.5% and 88.5%, respectively under BD_1.3, BD_1.5 and BD_1.7. 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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, CO₃^2–, HCO₃^–, SO₄^2–, 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.