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    Insights and Perspectives
    • Green Intelligent Fertilizer: From Interdisciplinary Innovation to Industrialization Realization

      ZHANG Fusuo, SHEN Jianbo, WEI Changzhou, MA Wenqi, ZHANG Weifeng, HUANG Chengdong, Lü Yang, ZHANG Lin, LU Zhenya, YING Hao, CHENG Lingyun, JIANG Rongfeng, QU Lingbo, HOU Cuihong, WANG Xinlong, XIU Xuefeng, MA Hang

      2022,59(4):873-887, DOI: 10.11766/trxb202203290145

      Abstract:

      As the material basis of food security, fertilizer plays an important role in supporting grain yield, agricultural product quality and human nutrition and health. Stepping into the new era, under the great situation of the national social economy, especially the green transformation of industry and agriculture, fertilizer innovation is facing the great challenge of synergistic realization of multiple objectives including food security, resource efficiency, environmental friendliness, nutrition and health, green and low carbon. In order to solve this major problem, the concept and industrialization pathway of green intelligent fertilizer were put forward in this paper. Through systematically elaborating the interactive principle of soil, plant, microorganism, fertilizer and environment, this study put forward a new academic idea for creating green intelligent fertilizer that matches soil, crops and climate and environmental conditions, and proposed its theoretical framework, key scientific issues, research and development pathways and future breakthroughs of green intelligent fertilizer. This study can provide new insights and reference for the design and implementation of holistic solutions for the green development of the whole industrial chain of multi-disciplinary cross-innovation and integration of industry and agriculture, aiming at promoting the green transformation and upgrading of China's chemical fertilizer industry and ultimately supporting the green development of agriculture.

    Reviews and Comments
    • Research Progress and Perspective on the Pollution Process and Abatement Technology of Herbicides in Black Soil Region in Northeastern China

      REN Wenjie, TENG Ying, LUO Yongming

      2022,59(4):888-898, DOI: 10.11766/trxb202107090354

      Abstract:

      Herbicides are important inputs in the agricultural chain of production required for the improved productivity of black soil granary. Nevertheless, the high-frequency and high-intensity application of herbicides in the black soil region in northeastern China might lead to their residual accumulation in soil. Thus, this affects the growth of after reap crops and becomes the bottleneck of crop rotation and planting structure adjustment. Therefore, research on the herbicide pollution process and key abatement technologies are of great scientific significance to ensure green sustainable development of agriculture in the black soil region. This paper systematically analyzed the research progress and development trend on herbicide pollution process and abatement technology in the black soil region. The scientific and technical problems existing in this research field was pointed out. Besides, we also put forward research ideas and key directions of herbicide pollution process and abatement technology in the black soil region in China, so as to promote the development of herbicide pollution and remediation theory and technology in the black soil region in China.

    • N2O Emissions from Black Soils in Northeast China

      ZHANG Nan, MIAO Shujie, QIAO Yunfa, CHEN Zengming, DING Weixin

      2022,59(4):899-909, DOI: 10.11766/trxb202106220322

      Abstract:

      Cropland is an important source of the potent greenhouse gas nitrous oxide(N2O). The cultivated black soils located in Northeast China play a vital role in national grain production. It has been demonstrated that the growth rate of N2O emissions from Chinese croplands is slowing down but still accelerating in the black soil area of Northeast China. Aiming at comprehensively assessing N2O emissions and understanding the production mechanisms, in this study, we summarized and characterized the N2O emission intensity, production processes and influencing factors from the black soils in Northeast China. The results showed that the average N2O-N emissions from unfertilized and inorganic-fertilizer applied black soils were 0.56±0.29 and 1.49±1.09 kg·hm–2, respectively. The inorganic fertilizer-N induced N2O emission factor(EF)was 0.45%±0.42% on average across the black soils in Northeast China. Both the background emissions and the EF values were generally lower compared with those of other uplands in China and black soils in other countries. This was likely due to the limitation of denitrification by labile carbon under normal rainfall conditions, and thus the N2O emissions were predominately derived from nitrification. It was found that the freeze-thaw cycles could greatly promote denitrification and result in large pulses of N2O fluxes during spring thaw, which might dominate the annual emissions. Compared with croplands in other regions of China, studies on the N2O emissions from black soils in Northeast China are largely limited. In future research, the in-situ observations of N2O emissions from black soils in different regions of Northeast China should be strengthened, and the mechanisms involved in freeze-thaw induced N2O emissions should be clarified. This will facilitate the evaluation of the response of N2O emissions from black soils to global climate change. Also, there is a need to strengthen researches on the effects of crop residue returning, manure application, etc. on N2O emissions, to facilitate the development of win-win strategies for enhancing soil quality and simultaneously reduce N2O emissions from black soils.

    • Research Progress on the Acid-base Properties of Variable Charge Soils Using Potentiometric Titration

      WEN Xiaocui, LI Jiuyu, SONG Jie, TAO Liang

      2022,59(4):910-923, DOI: 10.11766/trxb202010090558

      Abstract:

      Compared with the constant charge soils that distribute in temperate regions, the variable charge soils in tropical and subtropical zones are unique soils, with highly variable particle surface charges. Investigations on the surface chemical characteristics of variable charge soils have received considerable attentions. The potentiometric acid-base titration method is the most straightforward approach to qualitatively and quantitatively identify the surface chemical characteristics of variable charge soils. In this paper, the characteristics of variable charge soils are briefly described and the concept and difference of point of zero charge (PZC) is described and classified according to (i) the conditions for surface charge measurement, (ii) the modes of expression for PZC, and (iii) measurement methods for surface charge of soil colloidal particles. On this basis, the influence of the acid-base potentiometric titration setup conditions on the observed PZC, including co-existing ions, ionic strength of the solution, pre-equilibrium time, titration ranges, reaction atmosphere and titration method, is summarized and discussed. Furthermore, the research progresses on the application of potentiometric titration combined with surface complexation model (SCM, including diffuse layer model, basic stern model, triple layer model and distribution multi-site complexity and so on) to analyze the acid-base buffering capacity of variable charge soils were further summarized. Moreover, how related factors such as clay mineral composition, metal oxides, organic matter and other factors, affect the acid-base buffering capacity of variable charge soils are discussed. We believe that future studies on the variable charge soils could be carried out with the hope to:(1) establish a typical acid-base potentiometric titration method for all types of soils; and (2) verify if the combination of various surface complexation models could accurately quantify the acid-base buffer capacity of variable charge soils. It is hoped that this review can help soil science beginners to understand the basic concepts of variable charge soils, invite more researchers to pay more attentions to variable charge soils, and further encourage sustainable utilization of soil resources.

    • Rhizosphere Communication and Its Effects on Improving Phosphorus Utilization in High-input Vegetable Production System: A Review

      LI Huimin, WANG Rui, ZHONG Yueming, SHI Weiming, LI Yilin

      2022,59(4):924-934, DOI: 10.11766/trxb202007010354

      Abstract:

      Intensive vegetable production system with a high amount of phosphate fertilizer will cause phosphorus (P) resources waste and environmental risks caused by high accumulation of P in the soil. One of the effective methods to reduce P input and increase P use efficiency in vegetable fields is rhizosphere regulation, which could also improve P absorption and utilization by vegetables. This paper summarizes the major modules of rhizosphere communication, including plant-plant communication (vegetables intercropping root interactions), plant-microorganism communication (vegetable root and mycorrhizal fungi and rhizosphere bacteria interactions) and microorganism-microorganism communication (P solubilizing microorganism with rhizosphere microorganisms in vegetable fields) in promoting vegetable root development. Importantly, we discussed the mechanism (s) for activating soil accumulated P to increase the absorption and utilization of P by vegetables and its mechanism. In addition, different artificial regulation modules, such as increase P absorption and utilization of vegetables by applying P microbial fertilizer, and relieving the obstacles of continuous cropping of vegetables are discussed. Finally, the paper evaluated the direction of the rhizosphere communication in high-input systems to provided a theoretical basis for promoting the green and sustainable development of P fertilizer management in high-input vegetable planting systems.

    Research Articles
    • Evaluating the Regional Suitability of Conservation Tillage and Deep Tillage Based on Crop Yield in the Black Soil of Northeast China: A Meta-analysis

      JIANG Fahui, QIAN Yongqi, GUO Zichun, GAO Lei, ZHANG Zhongbin, CAO Zhen, GUO Jiaxin, LIU Feng, PENG Xinhua

      2022,59(4):935-952, DOI: 10.11766/trxb202202220070

      Abstract:

      [Objective] Black soil of Northeast China suffered serious degradation due to intensive farming in the past decades. To protect Black soil, conservation tillage is encouraged to be applied in this region. However, some studies have reported that this practice may reduce crop yield. Thus, our objective is to evaluate the suitability of conservation tillage and deep tillage in Black soil of Northeast China.[Method] We collected 543 yield comparisons from 61 papers published in international and domestic journals. After synthesis and grouping of required data, we analyzed the impacts of conservation tillage and deep tillage on crop yield and their influencing factors using meta-analysis as well as random-forest methods.[Result] Overall, crop yields were slightly increased under conservation tillage(+1.21%), but significantly enhanced under deep tillage(+12.3%) as compared with traditional rotary tillage. Conservation tillage caused a higher yield only at Liao River Plain(14.6%), whereas deep tillage increased yield by 10% across three plains including Sanjiang, Songnen and Liao River. Under conservation tillage, the yield effect size was most influenced by the mean annual temperature(20% contribution), mean accumulated temperature >10℃(19% contribution) and aridity index(16% contribution). For deep tillage, the most important factor was the topographic slope(14% contribution). Also, conservation tillage increased soil organic C mainly in the top layer and when combined with straw mulching reduced soil temperature remarkably and increased soil moisture. This observation was the main reason for yield reduction under this practice. Deep tillage reduced soil bulk density and penetration resistance significantly, leading to an increase in crop yield. After synthesizing the yield effect size and factor contribution, our results indicated that wind erosion sensitive regions such as western Liaoning and Jilin provinces as well as eastern Inner Mongolia are highly suitable for conservation tillage. On the other hand, the cold, humid, low-lying areas are more suitable for deep tillage, e.g., Sanjiang Plain and the typical Black soil belt.[Conclusion] This study evaluated the suitability of tillage practices in the Black soil of Northeast China based on the effect size of tillage on crop yield. The synthesized results suggest that conservation tillage is more suitable for dry and wind erosion sensitive regions or slopping lands where it can increase crop yield and protect soils as well.

    • Effects of Adding Woody Peat and Bentonite on Physical and Chemical Properties of Eroded and Degraded Black Soil

      ZHAO Xu, FAN Jun, WANG Xi, FU Wei

      2022,59(4):953-963, DOI: 10.11766/trxb202101150028

      Abstract:

      [Objective] Black land is a valuable land resource, which plays an important role in ensuring food security in the northeast region of China. In order to slow down the erosion and degradation of black soil farmland and improve farmland fertility, new soil management practices need to be developed.[Method] In this study, woody peat and bentonite were added to a typical eroded and degraded black land. The saturated hydraulic conductivity, air permeability and relative gas diffusion, water holding capacity, organic carbon content and crop yield were evaluated by the combination of indoor simulation and field in-situ observation.[Result] The results showed that:under indoor conditions, (1) adding 2% or 4% woody peat decreased the saturated hydraulic conductivity by 14.3% or increased it by 9.9%, increased the air permeability by 18.9% or 4.1%, increased the relative gas diffusion by 15.5% or 6.6%, increased the organic carbon content by 39.4% or 71.5%, and increased the yield of potted maize by 2.0 times or 1.9 times respectively; (2) adding 1% bentonite decreased the saturated hydraulic conductivity, air permeability and relative gas diffusion by 63.2%, 55.3% and 7.6%, and increased the organic carbon content and yield of potted maize by 1.0% and 1.1 times, respectively; (3) adding 2% or 4% woody peat and 1% bentonite decreased the saturated hydraulic conductivity by 65.8% or 73.1%, decreased the air permeability by 33.2% or 32.8%, increased the relative gas diffusion by 0.2% or 4.7%, increased the organic carbon content by 37.8% or 70.6%, and increased the yield of potted maize by 1.9 times or 1.5 times. The saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 75.0%, 32.0%, 36.1% and 43.2% respectively, and the air permeability decreased by 45.2% when woody peat was added to the eroded farmland. Also, the saturated hydraulic conductivity, air permeability and relative gas diffusion decreased by 39.1%, 44.4% and 44.0% respectively, while the organic carbon content and soybean yield increased by 3.6% and 4.2%, respectively, when bentonite was added to the eroded farmland. Even though there was no significant difference in organic carbon content and soybean yield; the soil saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 134.4%, 28.0%, 36.0% and 26.3% respectively, and the air permeability decreased by 38.2% when woody peat and bentonite was added to the eroded farmland. The addition of woody peat and bentonite could improve the water holding capacity of black land soils, and bentonite can retard the decomposition of organic carbon.[Conclusion] In general, the mixed addition of woody peat and bentonite has the best effect, which can effectively improve the soil aeration permeability, water holding capacity, organic carbon content and crop yield, and also help to accumulate organic carbon in the soil. It is an effective measure to rapidly improve the degraded black soil.

    • A Comparitive Analysis of Boundary Layer Methods in Solving Convectiondispersion Equation of Solute Transport

      WANG Jiao, SHAO Ming'an

      2022,59(4):964-974, DOI: 10.11766/trxb202009240537

      Abstract:

      [Objective] Understanding the behaviours of solute transport in soils is of great importance to agricultural management, resource utilitzation and environmental protection. Introducing boundary-layer theory to solve solute transport problems provides a simple and accurate alternative method to predict solute profile distribution and estimate transport parameters. Appropriate selection of boundary layer solutions requires an overall understanding of the characteristics of boundary layer solution accuracy under different conditions.[Method] This study compared the accuracy of the polynomial solution, exponential solution, combined solution, logarithmic solution and small flux solution based on multiple parameter combinations. Solute front movement with time in soil column experiments was further used to evaluate the performance of boundary layer solutions for parameter estimation.[Result] The accuracy of boundary layer solutions for predicting solute concentration profile increased first and then decreased with time. Comparison of different boundary layer solutions indicated that the cubic polynomial solution was optimal at the beginning while the exponential solution turned to be better afterwards for most cases. Importantly, the boundary layer methods performed better in estimating retardation factor than dispersion coefficient. The retardation factor obtained from boundary layer solutions was almost the same but with an exception of the small flux solution. The dispersion coefficient was greater than the breakthrough curve fitting method and varied between boundary layer solutions. The cubic polynomial and logarithmic solutions had a minimum error in the determination of the dispersion coefficient.[Conclusion] Boundary layer solutions can be used to accurately predict solute profile distribution for the early stage of solute transport processes. Cubic and exponential solutions had better performance than other solutions. Neverthless, cubic and logarithmic solutions can be the first choice for estimating parameters.

    • The Effects of Iron Oxide Phases Distribution on Aggregate Stability of Ferrisol Along a Subtropical Slope Derived from Granite

      XING Dengchun, CHEN Jing, BAO Haipeng, LONG Xiaoyong

      2022,59(4):975-986, DOI: 10.11766/trxb202009170519

      Abstract:

      [Objective] Iron oxides are sensitive to the pedogenic environment and an important cement of soil aggregates. The differentiation of iron oxide phases occurs at multiple scales in natural systems, which may affect the formation and stability of soil aggregates. This study aimed to explore the differentiation of iron phases, including total iron (Fet), free Fe-oxide (Fed), amorphous Fe-oxide (Feo), hematite (Hm), and goethite (Gt) at the hillslope, profile and aggregate scales and evaluate their effects on the stability of soil aggregates.[Method] A topo-sequence of Ferrisol, derived from granite in the hilly area of central Fujian Province, was fractionated into aggregates using wet-sieving and pipette methods. Fed and Feo in bulk soils and different aggregates were extracted with the citrate-bicarbonate-dithionite (CBD) solution and the acid ammonium oxalate (AAO) solution, respectively. Diffuse reflectance spectroscopy (DRS) was applied to determine Hm and Gt content. The percentage of water-stable aggregate (WSA) and the mean weight diameter (MWD) were evaluated.[Result] At the hillslope scale, the Fed and Fed/Fet in bulk soils decreased, while the Feo and Feo/Fed increased downslope. Meanwhile, the Hm and Hm/(Hm+Gt) significantly declined, while the Gt kept a little variation downslope. At the profile scale, the upper layers generally possessed higher contents of Fed and Gt, as well as lower levels of Feo and Hm in contrast to the deeper layers. At the aggregate scale, Fed, Feo and Gt were enriched in micro-aggregates. The contents of Hm were comparable in the micro- and macro-aggregates, while Hm/(Hm+Gt) increased with the aggregate size. Micro-aggregates were the main components, but the >0.25 mm macro-aggregates dominated the aggregate stability along the hillslope. The WSA of 0.5~0.25 mm and 1~0.5 mm aggregates were significantly positively correlated with Feo and Feo/Fed respectively, and the WSA of 2~1 mm macro-aggregate was significantly positively correlated with the Hm and Hm/(Hm+Gt).[Conclusion] The iron oxides demonstrated significant differentiation from hillslope scale to aggregate scale. The soil aggregate stability in the top-slope and bottom-slope profiles were higher than those in the transitional profiles due to the upslope enrichment of Hm and downslope enrichment of Feo along the hillslope.

    • Magnetic Characteristics of Yellow-Red Soil and Transformation of Its Magnetic Minerals, in Zhouning, Fujian Province

      LIU Xin, Lü Bin, ZHENG Xingfen, CHEN Zixuan, DU Jiahao

      2022,59(4):987-998, DOI: 10.11766/trxb202008240424

      Abstract:

      [Objective] In order to explore magnetic characteristics of the yellow-red soil in the subtropical region and transformation of the magnetic minerals in the soil under relatively humid and cold climate conditions, the author selected a profile of yellow-red soil (Profile ZN) derived from granite weathering crust in Zhouning County, northeast of Fujian Province. Under a mid-subtropical monsoon mountain climate, this area had an average annual temperature of 15℃, an average annual rainfall of 2 049.3 mm, and an elevation of 906.4 m counted from the bottom of the profile. The profile was about 1.9 m thick. With the floating soil on the surface removed, a total of 20 samples were collected at 10 cm intervals from the soil and weathering crust layers of the profile.[Method] In this study, room temperature magnetic parameters of the samples were measured, and thermomagnetic analysis conducted of representative samples, in combination of chroma, major geochemical elements and diffuse reflectance spectrum analyses.[Result] Results show:The profile was low in magnetic susceptibility, and relatively low in content of magnetic minerals, the upper part of the profile contained relatively more superparamagnetic particles, while the lower part did relatively more multi-domain particles. a*, b* and Ca*b* varied in the same trend, being the highest in Horizon B and the lowest in Horizon C, while b*/a* was high in the profile surface. The content of Fe2O3 increased with the degree of pedogenesis, indicating that during the soil forming process, other elements were leached while iron accumulated relatively. Iron content was not a major factor limiting magnitude of magnetic susceptibility. The profile was lower than those in the humid and hot low altitude tropical and subtropical regions in CIA (chemical index of alteration).[Conclusion] By comparing this profile with the three (NPN, PC-GL, PC-SY) in the adjacent area, the following conclusions were drawn:(1) Profile ZN contains relatively less magnetic minerals, which are composed of mainly ferrimagnetic mineral and small portions of maghemite, antiferromagnetic minerals hematite and goethite as well as paramagnetic minerals. Moreover, its content of goethite is higher than that of hematite. The magnetic particles in the lower part of the profile are coarser, and mainly multi-domain particles. And the particles get finer, and the portions of single-domain and superparamagnetic particles increase with decreasing soil depth. (2) Parent material and climatic conditions are two important factors contributing to the difference in magnetic characteristics between different profiles, and the climate conditions are the main ones controlling the content of secondary magnetic minerals (especially hematite and goethite). Chroma index b*/a* can be used to measure the content of goethite/hematite. (3) Under a relatively humid and cold climate the transformation of magnetic minerals in the soil is dominated by the transformation of strong magnetic minerals (magnetite and maghemite) into weak magnetic minerals (hematite and goethite). (4) Temperature, instead of precipitation, is the dominant factor influencing the content and relative proportion of goethite and hematite in the soil derived from granite weathering crust in humid subtropical regions.

    • Research on Spatio-temporal Heterogeneity of Soil Electrical Conductivity in Cotton Field Based on Electromagnetic Induction Technology

      FENG Chunhui, LIU Xinlu, JI Wenjun, WU Jialin, LIU Weiyang, PENG Jie

      2022,59(4):999-1011, DOI: 10.11766/trxb202010170576

      Abstract:

      [Objective] Characterizing spatial and temporal variability of soil salinity at field and landscape scales is important for a variety of agronomic and environmental concerns. In arid regios, soil salt content and its distribution position in the profile are important factors for the calculation of the irrigation quota of salinized soil. Due to the strong spatial variability of soil salinity content, the guiding value of soil surface salinization information for quota irrigation is very limited. A three-dimensional visualization study of the distribution and content of salinity in the soil profile is of great significance to the fixed irrigation of saline soil. The objective of this study was to evaluate apparent electrical conductivity (ECa) directed soil sampling as a basis for monitoring management-induced Spatio-temporal change in soil salinity.[Method] A soil salinity assessment study was conducted on an 18 hm2 saline-sodic field in Alar's Agricultural Science and Technology Park from March to November 2018. The study evaluated the three-dimensional spatio-temporal change that had occurred as a result of irrigation with drainage water over that period. Using geospatial electromagnetic induction (EMI) measurements of ECa and a spatial response surface sampling design 18 soil profile sites were selected and they reflected the ECa measurements every time. At each site soil profile samples were taken at 0.2 m intervals to a depth of 1 m and analyzed for electrical conductivity of the saturation extract (ECe). Also, the soil apparent conductivity data of four different periods and the electrical conductivity data of soil profile samples collected synchronously were analyzed. The inversion model between measured and apparent conductivity of different soil layers in the soil profile was constructed by the multiple linear regression method. Furthermore, the 3D visualization of soil salinity was realized by using 3D-IDW and the spatial and temporal changes of soil salinity in cotton field under mulch drip irrigation of Xinjiang were studied.[Result] The results showed that there was a good correlation between the apparent conductivity and the measured conductivity. The determination coefficient (R2) of the measured conductivity inversion model based on the apparent conductivity data was between 0.82 and 0.99. The results of 3D-dimensional data statistics of soil electrical conductivity showed that the distribution characteristics and content of soil salinity in different periods are quite different. These differences were attributed to human factors such as irrigation, film mulching and uncovering, and natural factors such as air temperature, evaporation and groundwater level. Also, the distribution type of soil salinity in March was uniform and the electrical conductivity range of the 0-100cm soil profile was 0.78 to 0.88 dS·m–1. The salinity in June and October was mainly concentrated in 0~20 cm and the electrical conductivity was 3.32 to 5.28 dS·m–1, respectively. Also, the electrical conductivity of 20~100 cm was 0.99~1.36 to 0.95~1.70 dS·m–1, respectively. In July, the salinity was mainly concentrated in 0~40 cm, and the conductivity in 0-40cm was 2.25~2.45 dS·m–1while the conductivity of 40~100 cm was 0.87~0.93 dS·m–1.[Conclusion] An assessment of three- dimensional spatio–temporal changes in soil salinity was conducted to provide a preliminary evaluation of the sustainability of irrigation quota on the Agricultural Science and Technology Park to ascertain its potential as an alternative for drainage water disposal. The results of this study can be used as guidance for accurate irrigation application in cotton fields.

    • Effects of Different Land-use Types on Physical and Chemical Properties of Coastal Saline-alkali Soils in Shandong Province

      LI Shan, YANG Yuechao, YAO Yuanyuan, LIU Yan, ZHANG Shugang, ZHANG Yanpeng

      2022,59(4):1012-1024, DOI: 10.11766/trxb202008310491

      Abstract:

      [Objective] The problems of high salinity, low nutrient and poor soil structure in the coastal saline-alkali area of Shandong province seriously affect the development of agricultural production. Therefore, the effective development and utilization of the soils in this region are of great importance to its agricultural production and income.[Method] In this study, the four land-use types (wasteland, grassland, cultivated land and forest land) in Kenli County of Dongying City were taken as the research objects, and the effects of different land-use types on the basic physical and chemical properties and aggregate stability of coastal saline-alkali soils were evaluated.[Result] The results showed that (i) the electrical conductivity (EC) and water-soluble K+ and Na+ contents in wasteland > cultivated land > grassland > forest land, with EC and Na+ content of wasteland being significantly higher than those from other sampling plots; (ii) the total nitrogen (N) and total organic carbon content (SOC) of the soils in forest land > grassland > cultivated land > wasteland, with SOC in the 0.25~2 mm water-stable aggregates being the highest; (iii) the mechanical stability mean weight diameter (MWD) and the mechanical stability aggregate content of > 0.25 mm particle diameter (R0.25) were significantly lower in forest land than those of other sampling plots; (iv) the water stability mean weight diameter (WMWD) and the water stability aggregate content of > 0.25 mm particle size (WR0.25) in wasteland were significantly lower than those in other sampling plots; and (v) the percentage of aggregate destruction (PAD) in wasteland > cultivated land > grassland > forest land. Additionally, results of the surface and internal scanning electron microscopy (SEM) of the 2 mm water-stable aggregates in grassland, cultivated land and forest land showed relatively obvious particles, pores, and adhesive materials. Furthermore, the Pearson correlation analysis showed that mechanical composition was significantly correlated with MWD and R0.25 while PAD was significantly correlated with soil water soluble Na+ content and SOC of 0.25~2 mm water-stable aggregate soil.[Conclusion] Different land-use types have different effects on soil physical, chemical, and mechanical properties. The grassland and forest land use types have significant ameliorating effects on the physical and chemical properties of coastal saline soil while forest land use has higher carbon reserves and aggregate water stability, but lower mechanical stability. The results of this study can provide references for the rational planning and sustainable development of land use in the coastal saline-alkali area.

    • The Spatial Variations of Saline-alkali Artificial Grassland on the Songnen Plain

      YANG Hongtao, WANG Zhichun, YANG Fan, An Fenghua, ZHANG Lu

      2022,59(4):1025-1035, DOI: 10.11766/trxb202101110601

      Abstract:

      [Objective] Grasslands in Songnen plain are propitious to the develop the mechanized-graziery due to its flat terrain and the climatic conditions, which influences by temperate continental monsoon climate. Moreover, influenced by the high plant coverage and diversity, black soil was developed, and the high quality forage species was dominated by Leymus chinensis in the past decades. However, the fragile eco-environment of Songnen grasslands could be impacted by the special topography, high salinity and shallow groundwater, and the parent material. Soil parameters are typically used to quantify the relationship between soil properties and forage yield and to identify the limiting factors of grassland productivity. Because of overgrazing and overdevelopment, the Songnen grasslands were degraded and salinized significantly. The husbandry was remarkable hindered by the low grassland productivity. The objectives of this study were:1) to investigate the spatial variation characteristics of soil physical and chemical properties; 2) to estimate the spatial variation characteristics of vegetation community; 3) to explore the potential linkages between dry yield of alfalfa and soil physical and chemical properties.[Method] The artificial grassland locates at the Xinfawopeng village of Baicheng City, which covers an area of 600 m×450 m. The soil sample points were set by grid method, with the spacing of each neighbor sample points was 50 m. The soil samples were collected from alfalfa artificial grassland from by cutting rings and soil auger in October 2017 and May 2018 for detecting the soil physico-chemical properties, meanwhile, the forage samples were collected in a quadrat of 1 m2 (1 m×1 m). All the soil samples were air-dried, ground and then passed through a 2-mm sieve for chemical properties. The 1:5 of soil-water extracts were used to determining soil pH, EC, Na+, Ca2+, Mg2+, HCO3, and CO32–. The spatial variations of soil properties, including soil mass water content (MWC), soil pH, EC, and total alkalinity (TA) were determined by classical statistics and geostatistics. Furthermore, the spatial variations of biological characteristics of artificial grassland, such as the Shannon-Wiener Index (SWI), dry yield (DY), shoot height (SH), and cover degree (CD) in the study area, were analyzed with classical statistics and geostatistics.[Result] At the depth of 0~30 cm, very high spatial variability of the EC and TA were found, however, the pH and MWC showed moderate spatial variations; The biological properties of the grassland community showed high spatial variations. Results of multiple linear regression (MLR-step wise) suggested that the alfalfa dry biomass (DM) could be predicted by (DM)=2699.73–276.496 pH (7.17< pH <9.76), which indicated that the soil pH influenced the alfalfa yield more than other soil properties.[Conclusion] The above results indicated that the soil physico-chemical properties of artificial grasslands in western Songnen pain were high and moderate spatial variations, and the alfalfa could not tolerance the pH higher than 9.76.

    • Identifying the Status of Heavy Metal Pollution of Cultivated Land for Tradeoff Spatial Fallow in China

      ZENG Siyan, YU Haochen, MA Jing, LIU Junna, CHEN Fu

      2022,59(4):1036-1047, DOI: 10.11766/trxb202009270541

      Abstract:

      [Objective] Farmland pollution affects national food safety and public health. From the perspective of soil pollution, clarifying the scale and spatial layout of fallow land at the national scale is of great importance. To restore heavy metal-contaminated farmland soils and ensure green development of agriculture, an urgent scientific solution is needed for soil pollution. In recent years, fallow has been pioneered as a means of recuperation and management of polluted farmland. However, some important management issues such as how much farmland should be fallowed, location of the fallow area, and how to fallow are yet to be defined at the national scale.[Method] In this study, we constructed a database of heavy metal pollution in Chinese farmland soils which comprised of 6 490 sample data from 2 343 farmland locations. These data were extracted from 569 published papers on the topic of farmland heavy metal pollution (Including combined pollution and single heavy metal pollution, such as Ni, Hg, As, etc.), published from 2000 to 2018 on Web of Science and China National Knowledge Infrastructure (CNKI). We assessed heavy metal pollution, the influence index of soil comprehensive quality, and the potential ecological risk to identify the spatial distribution of fallow priority grades, including urgent-fallow zone (I), regular-fallow zone (II), controlled-rotation zone (III), and general-rotation zone (IV).[Result] The results showed that the excessive concentration rates of heavy metals was Cd (18.03%)>As (2.95%)>Ni (2.26%)>Hg (1.55%)>Zn (1.42%)>Pb (1.34%)>Cu (0.49%)>Cr (0.10%). The proportions of soil environmental quality index such as severely, moderately and slightly exceeded were 1.71%, 3.89% and 23.84%, respectively. Also, the ratio of extremely strong and very strong potential ecological risk accounted for 0.29% and 2.89%. The ratio of the fallow area in China due to soil heavy metal pollution is 15.58%, of which the proportions of level I, II and III are 0.77%, 1.53% and 3.26%, respectively. Level I fallow areas are mainly distributed in 8 provinces of China including Henan, Hunan, Yunnan, Anhui etc. Additionally, fallow areas are mainly distributed in Henan and Hunan province, followed by Liaoning and Shandong province.[Conclusion] To promote the remediation of heavy metal pollution in Chinese surface soils, the implementation of differentiated fallow strategies for farmland areas with different pollution levels is recommended. This study shows the status of heavy metal pollution in farmland soils and spatially identified the urgency of fallowing areas in China. It also provides theoretical support for controlling farmland soil pollution and fallow space-time allocation in China.

    • Desorption of Sulfamethoxazole from a Soil-Microplastics Mixture System

      WANG Jiaqing, YU Ben, MA Shaofeng, CHEN Yiyang, LUO Yongming, ZHANG Haibo

      2022,59(4):1048-1056, DOI: 10.11766/trxb202101220038

      Abstract:

      [Objective] Desorption of antibiotics in soils in the presence of microplastics is key to its migration, transformation, and bioavailability. The objective of this study was to reveal the desorption characteristics of sulfamethoxazole in an artificial antibiotic contaminated soil in the presence of five different microplastics.[Method] Batch equilibrium desorption experiments were carried out using an acid paddy soil that was spiked with 33.4 mg·kg–1 sulfamethoxazole and was aged for 5 days before use. Five polymeric microplastics including polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET) (1.67% and 3.33%). The microplastics were added to the soil individually and a soil:solution ratio of 1:10 was maintained in the experiment. The supernate was sampled for the sulfamethoxazole analysis using high-performance liquid chromatography (HPLC) from 0.25 to 96 h during the desorption kinetic experiment. Also, different concentration of NaCl and fulvic acid were added into the soil-microplastics mixture system to study the effect of salinity and dissolved organic matter (DOC) on sulfamethoxazole desorption, respectively.[Result] The results indicated that the desorption rate of sulfamethoxazole declined significantly and a slow desorption phase was observed from 10 h to 48 h after the addition of polyethylene and polystyrene microplastics. The equilibrium desorbed concentration of sulfamethoxazole declined significantly (P < 0.05) in the presence of polyethylene and polyvinyl chloride microplastics. The influence of sodium and calcium ions on sulfamethoxazole desorption from the soil was not affected by the addition of microplastics. However, the influence of fulvic acid on sulfamethoxazole desorption was mitigated after the addition of microplastics in general. Importantly, with an elevated concentration of fulvic acid, the decline of sulfamethoxazole desorption was negligible.[Conclusion] Generally, the desorption of sulfamethoxazole from soils was altered in the presence of microplastics. In soils with a relatively high concentration of DOC, elevated sulfamethoxazole desorption was observed. Therefore, this study highlights the migration and bioavailability of sulfamethoxazole in soils contaminated with microplastics and how different solvents influenced its desorption.

    • Effect of Long-term Elevated CO2 Concentration on CH4 Emissions from Rice Paddy Fields

      YU Haiyang, WANG Tianyu, HUANG Qiong, ZHANG Guangbin, MA Jing, ZHU Chunwu, XU Hua

      2022,59(4):1057-1067, DOI: 10.11766/trxb202009110515

      Abstract:

      [Objective] Increases in atmospheric CO2 concentration have certain direct or indirect impacts on CH4 emission from rice paddy fields. So it is of great significance to have an in-depth study on impacts of long-term elevated atmospheric CO2 concentration on CH4 emission and related microorganisms for assessing and managing CH4 emissions from rice paddy fields in the context of future climate.[Method] To investigate effects of long-term elevated atmospheric CO2 concentration on CH4 emission and its mechanism, CH4 emission fluxes and abundance of the methanogens and methanotrophs under ambient CO2 (ACO2) and elevated CO2 conditions (ECO2) in rice paddy fields were monitored during the 2016-2017 season, with the aid of the Chinese rice FACE platform that has been operating for more than 10 years. Moreover, meta-analysis was conducted to determine quantitatively effects of elevated CO2 relative to duration on CH4 emission from and the abundances of methanogens and methanotrophs in rice paddy fields.[Result] Results show that compared with ACO2, long-term ECO2 significantly reduced CH4 emission and the abundance of methanogens by 28% and 39%, respectively (P<0.05), but increased the abundance of methanotrophs by 21% (P>0.05). Meta-analysis shows that with the increase in duration of CO2 elevation, the effect of elevated atmospheric CO2 concentration promoting CH4 emission and the abundance of methanogens gradually decreased, while the effect on the abundance of methanotrophs gradually increased.[Conclusion] Therefore, it could be concluded that under future climate conditions, long-term elevated CO2 will reduce CH4 emission from rice fields, which is of great significance for mitigating the greenhouse effect brought about by rice cultivation.

    • Comparative Study on Ammonia Volatilization from Soil Surface and Whole Shed in Solar Greenhouse

      ZHANG Zhaobei, LUO Wei, BAI Xinlu, CHENG Yuzhen, CHEN Zhujun, ZHOU Jianbin

      2022,59(4):1068-1077, DOI: 10.11766/trxb202101280056

      Abstract:

      [Objective] Ammonia volatilization from solar greenhouses driven by excessive nitrogen input has received widespread attention in recent years. However, the ammonia volatilization emission of greenhouse system is mainly determined by soil surface ammonia volatilization. Greenhouses are semi-closed structures, as a result, a part of NH3 emitted from soil can be absorbed again by the plant canopy or dissolved in the greenhouse membrane water and returned to the soil. The volatilization of ammonia from soil surface can not accurately reflect the amount of ammonia discharged into the atmosphere by solar greenhouse. Therefore, ammonia volatilization from soil surface is difficult to accurately reflect the amount of ammonia emitted into the atmosphere by solar greenhouse.[Method] Experiment comprised four treatments:(i) no nitrogen input with conventional irrigation (N0+FI), (ii) conventional nitrogen input with conventional irrigation (FT+FI), (iii) optimum nitrogen input with conventional irrigation (OPT+FI), and (iv) optimum nitrogen input with optimum irrigation (OPT+OI). Ammonia volatilization losses were measured in three vegetables seasons (tomato-watermelon-tomato) using intermittent closed chamber ventilation method. The air volume mask (Kanomax 6570) was used to measure the gas flow at the vent, and the ammonia concentration at the vent was continuously monitored by pumping method. In this way, the loss rate and amount of ammonia volatilization were measured from the whole greenhouse, and losses were compared with the soil surface.[Result] The results showed that the ammonia volatilization rate peaked on the same day after greenhouse fertilization, and there was no significant difference between fertilized and unfertilized (control) after 7 days. During the three planting seasons, the ammonia volatilization under different nitrogen treatments were:2.82-4.97 kg·hm–2, 6.59-9.97 kg·hm–2and 15.77-21.83·kg hm–2, respectively, and the corresponding ammonia volatilization emission factors were 0.64%-1.50%, 3.11%-4.21% and 2.59%-3.90%, respectively. The trend of ammonia volatilization rate of the whole shed was basically consistent with that of the soil surface. The ammonia volatilization rate of the whole shed was N 2.22 kg·hm–2 in the second quarter and N 2.92 kg·hm–2 in the third quarter, which accounted for 13.38%-33.69% of the ammonia volatilization from the soil surface, and the ammonia volatilization coefficient was only 0.46%-1.48%, which was much lower than the ammonia volatilization from the soil surface.[Conclusion] Thus, it is concluded that the ammonia volatilization from solar greenhouse will be overestimated when only taking the soil surface ammonia volatilization into consideration. Measuring ammonia volatilization based on the whole solar greenhouse system is thus recommended in future studies.

    • Leaching Is the Main Pathway of Nitrogen and Phosphorus Losses for Citrus Orchards with Sandy Soil in Three Gorges Reservoir Area

      LI Hongying, WANG Sichu, GAO Mengning, XIA Lizhong, HAN Qingzhong, WANG Qinglong, WU Yonghong

      2022,59(4):1078-1088, DOI: 10.11766/trxb202010200584

      Abstract:

      [Objective] Citrus production is one of the main income of farmers in the Three Gorges Reservoir area. The loss of nitrogen and phosphorus caused by excessive fertilizer in the Three Gorges Reservoir area present negative impacts on the aquatic environment.[Methods] In this study, sandy soil citrus orchard with natural grass mulching was chosen. The amount of nitrogen and phosphorus loss from surface runoff and leaching was observed for two consecutive years by plot experiment at six levels of fertilization. The pathways of nitrogen and phosphorus losses in the citrus orchard and the effects of different fertilization levels on nitrogen and phosphorus losses were investigated. Seven treatments were set in the experimental plot, with an average row and plant spacing of 4.7 m × 3.4 m; with no fertilizer application (T1) as the control, the application rates of nitrogen, phosphorus and potassium fertilizer for the T3, T4, T5, T6 and T7 treatments were 1.67, 2.33, 3.00, 3.67 and 4.33 times those of T2, respectively. During the growth season of navel orange in 2016—2017, rainfall and atmospheric deposition of nitrogen and phosphorus were monitored. Surface runoff water, sediment, and infiltration water were sampled for total nitrogen (TN) and total phosphorus (TP) content.[Results] Under the ecological protection mode of grass mulching, the surface runoff and soil erosion were effectively controlled. The main pathway of water loss in the rain-fed citrus orchard was leaching with a low coefficient of surface runoff and weak soil erosion. During the study period, the rainfall loss by seepage accounted for 48.9% of the rainfall, and the surface runoff only accounted for 1.73% of the rainfall. The amount of fertilization applied in deep furrow had no effect on the amount of nitrogen and phosphorus loss from the surface runoff. Leaching was the main pathway of nitrogen and phosphorus loss. The average leaching loss of total nitrogen and total phosphorus accounted for 99.0% and 76.9% of the total loss of nitrogen and total phosphorus respectively. Also, the amount of nitrogen loss (y) by seepage increased with the increase of application rates (x), and there was a significant linear correlation between them (y =0.35x–5.77, P<0.01). However, no significant correlation existed between the amount of phosphorus loss and application rates (P =0.05). Also, only a small amount of phosphorus can be leached to the bottom of the soil after the roots uptake and soil particles adsorption in up layers. Moreover, the residual phosphorus in the deep soil; after deep plough before citrus planting, had an impact on the leakage of phosphorus.[Conclusion] The problem of nutrient loss; leaching nitrogen loss in citrus orchards, in particular, should be given more attention. To reduce nutrient loss and achieve efficient utilization, nutrient management should be further optimized.

    • Effects of Litters and Phosphorus Addition on Soil Carbon Priming Effect in Pinus massoniana Forest

      MEI Kongcan, CHEN Yuehmin, FAN Yuexin, ZHOU Jiacong, ZHANG Qiufang, CHENG Lei, ZENG Quanxin, XU Jianguo, YUAN Xiaochun, CUI Juyan, LIU Yuanyuan

      2022,59(4):1089-1099, DOI: 10.11766/trxb202101130025

      Abstract:

      [Objective] Priming effect (PE) plays a critical role in the storage and turnover of soil organic carbon (SOC) in forest ecosystems. The intensity and direction of the priming effect, induced by litters, usually depend on the availability of limited nutrient (e.g., phosphorus, P), especially in subtropical highly weathered forest soils. However, how P and litters addition affect the soil priming effect in this region is not clear. This study aimed to investigate the effects of litter and phosphorus addition on SOC mineralization and priming effects in subtropical low-phosphorus soils and to provide a theoretical basis for the study of the carbon cycle in forest ecosystems in this region.[Method] Three kinds of 13C-labeled litters (Pinus massoniana, Michelia macclurei and Liquidambar formosana) and P (KH2PO4) were added to P. massoniana forest soil. The incubation of treated and control soils was conducted for 35 days in the laboratory. The physical and chemical properties, microbial properties and priming effect of the soils were determined after incubation.[Result] The results showed that the addition of the three kinds of litters significantly increased the soil native SOC mineralization, and produced a positive priming effect. The intensity of priming effect performance for P. massoniana > M. macclurei > L. formosana. In addition, litters addition decreased the content of soil inorganic nitrogen (nitrate and ammonium nitrogen, IN), but increased microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and β-glucosidase (βG) and acid phosphatase (ACP) activities. P addition alone significantly enhanced SOC mineralization, and the available phosphorus (AP), dissolved organic carbon (DOC), microbial biomass carbon (MBC), MBN, and MBP were also increased. Compared with the addition of litters alone treatment, the M. macclurei and L. formosana litters combined with P addition significantly reduced the priming effect and ACP activity. Linear regression analysis revealed that the cumulative priming effect was correlated negatively with soil AP, MBN and MBP content, whereas it was positively correlated with ACP activities.[Conclusion] The addition of litters stimulated microbial growth and as such promoted SOC mineralization and produced a positive priming effect. Also, the intensity of priming was mainly related to the quality of litters. Although P addition alone increased SOC mineralization, the influence of P added with litters on soil priming effect was dependent on the litter types; with low-quality litter having a lower soil priming effect.

    • The Subsequent Effects of Phosphorus Fertilization in Upland Red Soils and the Underlying Mechanisms

      SHI Wei, ZHANG Limei, WANG Jinsong, LI Congping, GU Chaoling, ZHAO Huiyu

      2022,59(4):1100-1111, DOI: 10.11766/trxb202106220680

      Abstract:

      [Objective] The utilization efficiency of phosphorus fertilizer is generally low in agro-ecosystems as phosphorus is readily co-precipitated with iron and manganese oxyhydroxides, iron aluminides, or directly adsorbed to the soil minerals, particularly in the red soil ecosystem. Thus, understanding the subsequent effects of phosphorus retained in the soil on soil ecological function and crop nutrient supply is of significance to guide the management of phosphorus fertilization.[Method] Based on a long-term fertilization experiment in red upland soil, this study investigated the effect of the conventional fertilization (CK) and short-term phosphorus fertilizer input (at rates of 0, 50, 100, 150 and 1 000 kg·hm–2, P2O5) on soil nutrients, soil nitrogen cycle process and crop yields after 27 years. We evaluated the relationship between these factors and the residual effect of phosphorus using the multivariate statistical analysis method.[Result] Short-term P fertilizer addition at a high rate (1 000 kg·hm–2, P1000) had no significant effects on soil total carbon (TC), total nitrogen (TN) and microbial biomass (MBC) compared to the conventional fertilization treatment (CK). Also, it significantly increased soil pH, nitrogen mineralization rate (Nmin), soil nitrogenase activity (SNA), and potential nitrification rate (PNR) (P < 0.05), while it significantly decreased the net N2O emission potential (NN2O) (P < 0.05). Compared with the low phosphorus dosage treatments (50, 100, 150 kg·hm–2), P1000 significantly increased soil available phosphorus (AP), Nmin, SNA, PNR and potential N2O production rate (PN2O) by 33.3%-76.4%, 88.2%-388.1%, 111.4%-4 826.3%, 22.6%-152.4% and 13.8%-78.9%, respectively (P < 0.05), but significantly decreased the net N2O emission potential by 64.6%-78.9% (P< 0.05). These results suggest that the application of a high dosage of phosphorus fertilizer has a strong residual effect on soil microbial activity and nitrogen processes even after 27 years. Spearman correlation analysis and redundancy analysis showed that AP and pH were the most important factors affecting soil microbial activities. Maize yield in the recent three years showed no significant difference among all treatments but was significantly positively correlated with TP, AP and pH. In comparison to low phosphorus treatments, P1000 treatments showed a promotion effect of 3%-23% on maize yield based on the historical yield data during 1991—2019.[Conclusion] Our results reveal that the short-term application of a large amount of phosphorus fertilizer has significant positive effects on maintaining soil fertility, microbial activity, soil nitrogen cycle function activity and crop yield even after 27 years, owing to the promotion of soil pH and slow release of available phosphorus.

    • Biological Effect of Trichoderma-enriched Biofertilizers on Cabbage Cultivation in Coastal Saline Soil

      YU Ya'nan, WU Haiyan, WANG Panxing, DING Mingyue, MA Xingcong, JIANG Siqi, CAI Feng, SHEN Qirong, CHEN Wei

      2022,59(4):1112-1124, DOI: 10.11766/trxb202009100511

      Abstract:

      [Objective] The area of coastal saline soil is recognized as an important land resource with utilization value for agriculture. However, coastal mudflat area is usually characterized by poor plant growth and low microbial activity due to its high salinity suppressing most crops via the high osmotic stress, nutrient deficiency, toxicity and poor physical soil conditions. Soil microbes like Trichoderma spp. play a significant role in assisting plants to tolerate salinity stress. The present study aimed to investigate the effect of two Trichoderma-enriched bio-organic fertilizers on the yield and quality of cabbages (Brassica oleracea L.) grown in coastal saline soil as well as their effect on soil nutrient availabilities.[Method] Field and pot experiments were carried out with eight treatments:100% chemical fertilizer (CF), 30% bio-organic fertilizer plus 70% chemical fertilizer, 60% bio-organic fertilizer plus 40% chemical fertilizer, 100% bio-organic fertilizer (without chemical fertilizers), and using the non-fertilization treatment as the control (CON). The two bio-organic fertilizers were respectively prepared with strains of Trichoderma guizhouense NJAU 4742 (which is commercially available in China as a plant-growth-promoting agent) and T. arenarium 1A131 (which was previously isolated from saline mudflat of Dafeng, Jiangsu). The nutrient load of the seven fertilization treatments was set up to equal in the aspect of the contents of total N, P and K.[Result] Results obtained from both the field and pot experiments demonstrated that there was no significant difference in the effect of the two bio-organic fertilizers. Compared to the non-fertilized control (CON) and the full chemical fertilization (CF), 30% or 60% bio-organic fertilizer significantly increased the contents of nitrate N and available P in soil. The treatment of 60% bio-organic fertilizer plus 40% chemical fertilizer influenced the cabbage growth by significantly (P< 0.05) promoting the biomass of shoot and roots, and the chlorophyll content (shown by the SPAD values) in leaves. Among the fertilization treatments, application of 60% bio-organic fertilizer plus 40% chemical fertilizer resulted in the significantly highest yield and best quality of cabbage heads (with increased sugar and vitamin C contents, and less nitrate accumulation, P < 0.05). Moreover, principal component analysis (PCA) demonstrated that the significantly better plant growth effect did not correspond to the variation of soil nutrients. Rather, it may be related to the loaded microbes which were previously reported to be able to promote plant growth via producing phytohormones and activating the local microbiome.[Conclusion] Application of 60% bio-organic fertilizer combined with 40% chemical fertilizer, which allows the roots to develop to the maximum in such a saline ecosystem, is the optimized fertilization regime to cultivate cabbages in saline agriculture in coastal mud flats. Besides, compared to the nutrient load from the fertilizers, the function of the Trichoderma strains was found to be more directly linked to the plant-beneficial effect of this fertilization regime. The biological effect from the applied strains did not significantly rely on the origination of a specific strain. Moreover, the requirement of applying a local saline soil strain to the saline agriculture was not fully addressed here at least not in this study, and thus, needs further investigations.

    • Characteristics of Rhizosphere Microbial Communities in a Diseasesuppressive Soil of Tomato Bacterial Wilt and Its Disease-suppressive Transmission Mechanism

      LIU Hong, DONG Yuanhua, SHEN Minchong, SUN Feifei, WANG Xia, LIU Jingping, LI Jiangang

      2022,59(4):1125-1135, DOI: 10.11766/trxb202101200037

      Abstract:

      [Objective] Microorganisms in the rhizosphere play an important role in the process of plants resistance to soil-borne diseases. This study investigated the characteristics of rhizosphere microbial community and the mechanism of microbial community assembly in disease-conductive soil and disease-suppressive soil in a tomato-cultivated field.[Method] Real-time quantitative PCR was applied to detect the pathogen density in disease-conductive rhizosphere soil and disease-suppressive rhizosphere soil. Also, the distinction of tomato rhizosphere soil microbial community diversity, composition, structure, and assembly processes based on zero model were analyzed through high-throughput sequencing of 16S rRNA gene amplicon.[Result] Results show that, compared to disease-conductive soil, there was a significantly lower disease index of tomato bacterial wilt in disease-suppressive soils (disease index in disease-conductive soil and disease-suppressive soil were 47.5 and 22.5, respectively). The rhizosphere bacterial communities in disease-suppressive soils were characterized with higher alpha diversity, more abundant beneficial microorganisms, such as Actinobacteria, Firmicutes, Bacillaceae, and Streptomycetaceae, lower abundance of Ralstonia solanacearum (abundance of pathogenic bacteria decreased by 12.22 times) and accompanied with more stochastic processes. This shows that the adaptability of disease-suppressive soil to pathogenic disease stress was stronger than that of disease-conductive soil. The disease-conductive soil and disease-suppressive soil were mixed in a certain proportion to form three treatments; disease-conductive soil alone (D10H0), a mixture of disease-conductive soil and disease-suppressive soil with a mass ratio of 1︰1 (D5H5), and disease-suppressive soil alone (D0H10) to test the transmitability of inhibition properties of disease-suppressive soil. It was observed that with the increase in the proportion of disease-suppressive soil, the disease index of tomato bacterial wilt gradually decreased (the disease index in D10H0, D5H5, and D0H10 were 41.67, 29.17, and 16.67, respectively). While the diversity of bacterial alpha gradually increases, the abundance of Firmicutes, Streptomyces, and Bacillaceae increase significantly. Also, the dominant role of the stochastic and random processes is strengthened.[Conclusion] Disease stress had a significant effect on the alpha diversity, composition, structure, and community assembly process of the tomato rhizosphere microbial community. The disease-suppressive soil can recruit more beneficial microorganisms through plant roots to resist pathogenic disease stress.

    • Molecular Phylogeny Suggests a Key Role of ATPase Genes on Evolutionary Adaption of Soil Ammonia-oxidizing Archaea to Acid Stress

      SONG Yuxiang, WANG Baozhan, QIN Hua, KUANG Lu, TANG Xiufeng, WANG Xinxin, ZHOU Xiaoli, JIA Zhongjun

      2022,59(4):1136-1147, DOI: 10.11766/trxb202101310062

      Abstract:

      [Objective] Ammonia-oxidizing archaea (AOA) is considered the main microbial group catalyzing the nitrification process in acidic soils. However, how AOA adapts to acid stress remains largely uncertain, and we hypothesize that the gene encoding ATPase for microbial energy metabolism may likely play a key role in the adaption of AOA to acidic stress in these soils.[Method] In this study, 736 billion base pairs were obtained by ultra-deep metagenomics sequencing of acidic soils of Masson pine plantations with five different planting years (15 a, 24 a, 45 a, 55 a, 63 a). The phylogenetic congruency between the AOA amoA gene and ATPase subunit A gene was reconstructed to study the molecular mechanism that may enable the acidophilic lifestyle of AOA.[Result] The habitat expansion of AOA to the acidic environment cannot be explained by the phylogenetic evolutionary trajectory of canonic amoA genes encoding ammonia monooxygenase. The dominant AOA taxa from all 5 forest soils were phylogenetically affiliated with Nitrososphaerales and Ca. Nitrosotaleales based on amoA gene phylogeny. Even though Nitrososphaerales is more distantly related to Ca. Nitrosotaleales, it is more closely related to neutral AOA in alkaline soils. Therefore, the phylogenetic law based on the amoA gene cannot explain the successful colonization of Nitrososphaerales in acidic soils. The phylogeny of ATPase subunit A genes indicated a single clade of AOA in all acidic forest soils. These results thus suggest that during the habitat expansion and evolution of AOA, the amoA and ATPase genes could have experienced different selection pressures to cope with acid stress, and the V-ATPase gene may be obtained through horizontal gene transfer to adapt to acid stress. With the increase in forest age, the abundance of Ca. Nitrosotaleales group first decreased and then increased, while the abundance of Nitrososphaerales group first increased and then decreased. Also, it was observed that soil bioavailable potassium is an important environmental factor that significantly affects the structure of the AOA community.[Conclusion] These results indicate that the AOA populations in acid plantation soils under different planting years were clearly differentiated, and the horizontal transfer of V-ATPase gene may be an important mechanism that enables AOA to survive acidic stress for the habitat expansion.

    • Long-term Straw Mulching Affects Rice and Wheat Yields, Soil Nitrogen Fractions, and Microbial Community under a No-till System

      ZHOU Zijun, GUO Song, CHEN Kun, ZENG Xiangzhong, SHANGGUAN Yuxian, YU Hua, QIN Yusheng, TU Shihua, HE Mingjiang, LI Lijun

      2022,59(4):1148-1159, DOI: 10.11766/trxb202011190522

      Abstract:

      [Objective] Conservation tillage has attracted increasing attention over recent decades due to its benefits in improving soil quality. A 12-year fixed field experiment was conducted to assess the effects of long-term straw mulching on yields of rice and wheat, soil nitrogen fractions and microbial community with soil layers under a no-till system in Southwestern China.[Method] Two treatments, no-till without straw mulch (NT) and no-till with straw mulch (NTS), were used for the experiment. The soil was sampled at 0-5, 5-10, 10-20, and 20-30 cm soil layers. Soil total nitrogen (TN) and labile nitrogen fractions, including particulate organic nitrogen (PON), microbial biomass nitrogen (MBN), NH4+-N, NO3-N, and dissolved organic nitrogen (DON) were analyzed. Soil microbial community was determined using phospholipid fatty acid (PLFA) analyses. Crop yields were measured from September in 2013 to May in 2018.[Result] The results showed that compared to the NT treatment, the NTS treatment significantly increased wheat yield by 6.49%, with negligible effects on rice yield. The NTS treatment increased the contents of soil TN at 0-5 cm soil layer, NH4+-N and NO3-N at 0-5 cm layer, PON at 0-5 and 5-10 cm layers, and DON at 0-5 and 10-20 cm layers but not MBN content. Also, the NTS increased the DON/TN ratio at 0-5 and 10-20 cm layers rather than the ratios of other labile nitrogen fractions to TN. Soil total microbial PLFA and bacterial PLFA were higher in the NTS than in the NT treatment. Additionally, fungal and actinobacterial PLFA were comparable between the two treatments, leading to a lower fungal/bacterial ratio in the NTS. Principal component analysis revealed that the soil microbial community at 20–30 cm layer was separated from the other three soil layers, and soil microbial communities of NTS treatments were generally separated from NT treatments along the first principal component axis. Furthermore, redundancy analysis demonstrated that soil MBN, TN, and ratio of particulate organic carbon to PON were key factors in shaping soil microbial community. Soil TN, labile nitrogen fractions, and microbial PLFA fractions decreased with increased soil layers, irrespective of straw mulching status.[Conclusion] Straw mulching should be recommended to no-till systems in Sichuan province, Southwestern China because it leads to effective improvements in soil nitrogen contents, wheat yields, and soil total microbial PLFA.

    • Effects of Different Ameliorative Measures on the Enzyme Activities of Quaternary Red Soil

      ZHAO Jing, WANG Yanan, ZENG Xibai, WEN Jiong, WEN Yunjie, WU Cuixia, ZHENG Zhong

      2022,59(4):1160-1176, DOI: 10.11766/trxb202008100444

      Abstract:

      [Objective] Red soil is one of the important soil types in China. Its low fertility is a problem for agricultural output. Exploring the effect of different improvement measures on soil fertility is integral for realizing sustainable use of middle and low yield fields.[Method] In this study, dryland red soils derived from Quaternary red earth were collected from a field experiment in Yueyang, Hunan Province and used to measure the changes in soil pH and nutrient contents across different soil layers and years of different treatments. These treatments included fallow (F), no fertilizer control (CK), a single application of inorganic fertilizer of nitrogen, phosphate, and kalium (NPK), inorganic fertilizer combined with straw-return (NPKS), inorganic fertilizer combined with lime (NPKL), inorganic fertilizer combined with amendments of organic crushed-bones (NPKA), and inorganic fertilizer combined with commercial bio-organic fertilizer (NPKC). We also compared the activity of enzymes related to carbon, nitrogen, and phosphorus cycles in this soil using the microplate fluorescence method.[Result] Some treatments significantly affected soil nutrients and enzyme activities. Soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) in the 0-20 cm soil layer treated with NPKC in 2020 increased by 73%, 29%, 61%, and 1 847%, respectively, relative to the control. This treatment also significantly increased the enzyme activities of the enzymes that participate in the carbon cycle, including α-1, 4-glucosidase (αG), β-1, 4-glucosidase (βG), β-1, 4-xylosidase (βX), and cellobiohydrolase (CBH). Also, the activity of β-1, 4-N-acetylglucosamine (NAG), which is involved in the nitrogen cycle, was increased. Correlation analysis showed that SOM was significantly positively correlated with enzyme activities of αG, βG, βX, CBH, and NAG (P < 0.01). Additionally, the pH value was significantly negatively correlated with acid phosphatase (ACP) activity (P < 0.01). The effect of improvement measures on the enzyme activity of 0-20 cm soil layer was greater than on deeper layers. In 2019, compared with the control, NPKA treatment increased CBH enzyme activity in the 0-20 cm soil layer by 352%, but only by 2% in the 20-40 cm soil layer. Besides, ACP enzyme activity in the soil also showed a trend of increasing with years of treatment.[Conclusion] The combination of inorganic fertilizer and organic materials can significantly improve the nutrient status and soil enzyme activity in red soils. This can be used to efficiently improve the fertility of barren red soil.

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      • 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.

      • Progress of Functional Genes Related to Soil Nitrogen Cycling Based on Knowledge Mapping

        wu han qing, ruan chu jin, wan wei, li sheng long, pei ding yi, han miao, chen guo wei, liu ying, zhu kun, wang gang

        DOI: 10.11766/trxb202110270580

        Abstract:

        Functional genes related to soil nitrogen (N) cycling are widely involved in a series of ecological processes, including N fixation, ammonification, nitrification and denitrification, and are key components of the N biogeochemical cycling, which greatly affects soil productivity, carbon neutralization, and agricultural sustainable development, as well as global environmental changes. In recent decades, the rapid development of molecular and microecology technology has promoted the research about functional genes related to soil N cycle and their microbial functional communities. In order to objectively and analyze the research trends, hotspots, and historical trends in the field of functional genes related to soil N turnover, the pertinent literature retrieved from the Web of Science database from 2001 to 2020 was analyzed from four aspects of publications amount, highly cited papers, high-frequency keywords and historical direct citations based on knowledge mapping. The results showed that: (1) The application of molecular biology techniques to excavate the functional genes and community structure related to soil N turnover so as to explore the microbiological mechanism is the current hotspot and entry point in the research field. (2) The research about soil N turnover functional genes mainly focused on three aspects: 1) Using metagenomics and other technologies to screen, identify and annotate the functional genes related to soil N turnover, so as to discover new microbial functional gene sequences and updates primer database, etc.; 2) Effects of environmental factors and agricultural management practices on soil N turnover related microbial indicators; 3) Using functional gene abundance to characterize the soil N cycling processes-related functional microorganisms, as well as analyze the relationship between functional genes, soil properties, and microbial community structure, in order to reveal the molecular mechanism of soil nitrogen turnover. 3) The historical development context of soil N turnover functional genes was from the screening, identification, identification, corresponding primer design and analysis method determination of N-cycling functional genes, to the influencing factors (or environmental conditions) of soil N turnover functional genes, combined with the current data of the activity, abundance of functional genes related to soil N turnover, and functional microbial populations, community structure and even soil properties, to comprehensively explore the microbial mechanism of soil N cycling.

      • 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.

      • Effect of Different Rice Planting Years on Pore and Infiltration Properties of Soda Saline-alkali Soil

        ZHOU Bin, HU Shuwen

        DOI: 10.11766/trxb202105180262

        Abstract:

        [Objective]The existing scientific literature and production practice have proved that rice planting can effectively improve soda saline-alkali soil. However, there is still a lack of research on how rice planting affects soil structure and infiltration performance to improve saline-alkali land. [Method] In this paper, the pressurized mercury method was used to study the micro-pore changes of soil in different years of rice planting and the difference of soil infiltration performance was studied by soil column experiment, to clarify the influence of rice planting on the change of saline-alkali soil structure and infiltration performance. [Result] The result show that the average pore size of soil increased with an increase in the planting years. Specifically, the average pore size of soil in the 7th year increased by 0.808μm compared with that in the 1st year. Also, the specific surface area of soil decreased with an increase in planting years, and the specific surface area of soil after 7 years was decreased by 0.087m2·g-1 compared with that after one year. Soil porosity increased with the planting years, and the soil porosity after 7 years was increased by 8.35% compared with that in the 1st year. With the increase of planting years, the number of small pores decreased while that of large and medium pores increased. The pore size of the soil planted for 7 years was 28.25% (ranging from 30~75μm) and 12.45% (ranging from 75~200μm). Also, the infiltration performance of the soil was also significantly improved. The steady infiltration rate of soil planted for 7 years was 107 times higher than that of waste land. [Conclusion] Planting rice in saline alkali land is conducive to the formation of soil pores and the transformation from small pores to large and medium pores. The increase of soil pore size and porosity can effectively improve soil structure and improve soil infiltration performance. Under the experimental conditions, the leaching rate of salt in saline-alkali soil was increased, thereby enhancing the desalination efficiency of the soil tillage layer.

      • 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.

      • 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

        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.

      • 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.

      • 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

        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.

      • 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.

      • Environmental Behavior and Control of Antibiotic Resistance Genes in Soil – A Review

        SHENG Hong-jie, WANG Fang, XIANG Lei-lei, FU Yu-hao, WANG Zi-quan, XU Min, MEI Zhi, LIU Yu, DOU Qing-yuan, JIANG Xin, JAMES M. Tiedje

        DOI: 10.11766/trxb202111100608

        Abstract:

        Over the past several decades, the long-term misuse and abuse of antibiotics in human health and livestock production have significantly contributed to the widespread dissemination of antibiotic resistance. Antibiotic resistance has been regarded as the top of the six emerging environmental issues and global challenges humans face in this century. Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in natural and agricultural environments such as soil may have a substantial impact on the spread of resistance determinants to the human microbiome. Research on the distribution, source, diffusion and elimination techniques of ARGs in soil has become a hot topic. ARGs have been widely identified in diverse environments affected or unaffected by human activities, including soil, water sources, and atmosphere. Soil undoubtedly contains a complex natural resistome and also acts as a key reservoir for ARB and ARGs in the environment. The ARGs in soil primarily originate from internal resistance and external input. The internal resistance in microorganisms mainly indicates the presence of ARGs in the genomes of microbes. However, the antibiotic resistance in microbial can also be ascribed to the random mutation of genes under special conditions. In addition, with the widespread use of antibiotics in clinical care, livestock and agricultural production, more ARB and ARGs are introduced into the soil, resulting in an increased enrichment of ARGs. The transfer of ARGs often occurs via environmental media. However, recent studies have shown that they may also be transmitted between parents and offspring or among different species of bacteria by vertical and horizontal gene transfer (HGT), respectively. ARGs in the soil can be transferred to surface/groundwater, atmosphere and the phytosphere. Both natural factors and human activities play vital roles in ARGs transmission in soils. For example, soil physicochemical properties (pH, organic matter, water content, etc.), agronomic regulations (cropping patterns, reclaimed water irrigation, organic fertilization, etc.), and environmental contaminants (heavy metals, nanoparticles, microplastics, etc.) can significantly affect the structural diversity and function of soil microbial communities. They have been identified as important environmental pressures that induce the evolution and spread of antibiotic resistance. ARGs are also identified in human clinical pathogens conveyed by soil microbes. When comparing the multidrug-resistant resistome of soil bacteria with those in clinical human pathogens, the functional metagenomic analysis indicated a high nucleotide identity (>99%). This inferred possible HGT among bacteria from various environments. To reduce the threat posed by ARGs, treatment measures (aerobic composting, anaerobic digestion, and wastewater treatment technologies) have been examined to alleviate the selective pressure and reduce the import of ARGs into the soil. Generally, the reduction of ARGs in the environment is mainly related to extracellular DNA and cell transport, death of the host, and attenuation of extracellular ARGs. Although the threat of ARB and ARGs to humans is generally recognized, it is difficult to determine threshold values for the maximum admissible levels of ARB and ARGs in diverse environments highly related to human activities. Furthermore, there is insufficient information to quantitatively evaluate the associated human health risks. Considering the urgency of the problem, it is necessary to establish a global systematic and publicly available monitoring network, for consecutively measuring antibiotic usage and the diversity of antibiotic resistance from clinical and agricultural practices. Continuous surveillance of antibiotic resistance can contribute to disease therapy, effective antimicrobial management and policy formulating. Thus, the “One-Health” theory was proposed to manage the development and spread of ARGs in an interdisciplinary manner, and holistically reduce human risk to the lowest level. More attention should be paid to ARGs pollution with investment in both fundamental and applied research, to provide a strong scientific basis for formulating effective alleviation actions and a standardized assessment system. This will serve as a baseline for preventing, reducing, and removing these environmental contaminants.

      • 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.

      • Effects of Long-term Application of Phosphorus and Organic Fertilizer on Transformation of Zn Forms in Yellow Paddy Soil

        LIU Yanling, LI Yu, JIANG Taiming, ZHANG Yarong, HUANG Xingcheng, ZHU Huaqing, YANG Yehua, ZHANG Meng, ZHANG Wen’an, ZHANG Yan

        DOI: 10.11766/trxb202107290283

        Abstract:

        【Objective】To investigate the variation of zinc (Zn) speciation in yellow paddy soil under different long-term fertilization and its effect on available Zn, a field experiment was designed in 1995. 【Method】There were six treatments: the control (no fertilizer, CK), P deficiency (NK), balanced application of chemical N, P and K fertilizer (NPK), single manure (M), lower organic and inorganic fertilizer combination treatments (0.5 MNP), and higher organic and inorganic fertilizer combination treatments (MNPK). The change process of soil available Zn and the temporal variation of different forms of Zn were studied. Also, the relationship between different forms of Zn and available Zn was analyzed with correlation and path analyses. 【Result】The results showed that the available Zn and Zn activation coefficient of soil with NK treatment decreased with the increase of experimental years. During this time, the linear fitting formula of the Zn activation coefficient reached a significant level, and the annual growth rate was -0.052 percentage points. Compared with NK treatment, the available Zn and Zn activation coefficient of soil with NPK treatment increased by 44.1% and 1.49 percentage points, respectively in 2019. Also, the contents of weak acid soluble Zn and reducible Zn increased by 15.9% and 5.3%, respectively. For treatments with organic fertilizer, the available Zn and Zn activation coefficient of soil increased linearly with the increase of experimental years, and the annual growth rate was 0.074-0.1244 mg?kg-1and 0.032-0.063 percentage points, respectively. Compared with NPK treatment in 2019, the available Zn and Zn activation coefficient of soil in the manure treatments increased significantly by 6.3%-22.6% and 0.68-1.47 percentage points, respectively. For these treatments, the contents of weak acid-soluble, reducible, and oxidizable Zn increased significantly by 33.6%-84.0%, 32.5%-47.4%, and 25.5%-36.3%, respectively. In addition, the proportions of weak acid-soluble, reducible, and oxidizable Zn increased significantly by 0.6-1.3, 1.7-3.4, and 1.2-7.3 percentage points, respectively. On the contrary, the proportion of residual Zn was observed to decrease by 3.6-12.0 percentage points. Correlation analysis showed that soil available Zn was significantly positively correlated with weak acid-soluble, reducible, and oxidizable Zn, but significantly negatively correlated with residual Zn. Path analysis results showed that the direct path coefficient of weak acid-soluble Zn was the largest and had a significant direct positive effect on available Zn, residual Zn showed a significant direct negative effect on available Zn, while reducible and oxidizable Zn indirectly affected weak acid soluble Zn and had a strong indirect positive effect on available Zn. 【Conclusion】The weak acid-soluble Zn was the main source of available Zn in yellow paddy soil, while reducible and oxidizable Zn were the important cache database of available Zn. In agricultural production, the soil Zn efficiency could be improved by applying organic fertilizer reasonably to promote the transformation of Zn to weak acid-soluble, reducible, and oxidizable Zn, and avoid the accumulation of Zn in the residual state.

      • Effects of Shrub-encroached Grassland on the Stability of Soil Aggregates and Cementing Materials in Alpine Grassland of Qinghai-Tibet Plateau

        CHEN Hong, MA Wenming, WANG Changting, DENG Zengzhuoma, TANG Sihong, HOU Chen

        DOI: 10.11766/trxb202107290253

        Abstract:

        【Objective】Soil aggregate is an important storage unit of soil organic carbon, and its stability directly affects the sequestration of organic carbon. This study explored the effects of shrub encroachment on the stability of soil aggregates and their cementing materials in grassland.【Method】The content of soil aggregates and their cementing materials (soil aggregate organic carbon, Fe-Al oxides, Ca bond organic carbon, and Fe-Al bond organic carbon) and the stability of aggregates (the content of aggregates >0.25 mm, mean weight diameter/MWD and fractal dimension) were determined at four typical shrub-encroached grasslands (Spiraea alpina, Sibiraea angustata, Caragana microphylla, Potentilla fruticosa) in the eastern margin of the Qinghai-Tibet Plateau. 【Result】 The results show that shrub encroachment significantly decreased the aggregate content of 2~0.25 mm and <0.002 mm and aggregate stability in the Caragana microphylla plot. However, there was no significant effect on the other three shrub grasslands. Shrub encroachment mainly changed the content of cementing substances in the aggregates of the Caragana microphylla and Sibiraea angustata plot. The results of boosted regression tree analysis between cementing materials and MWD show that the main contributing factors to the stability of aggregates in Spiraea alpina polt were complexed iron (Fep) and amorphous iron and aluminum (Feo, Alo). Also, the major contributors to grassland and other shrub plots were soil aggregate organic carbon (SAOC) and free iron oxides (Fed). 【Conclusion】 Although shrub encroachment increases the content of main cementing material—SAOC in <0.053 mm in Caragana microphylla plot, it reduced the content of large aggregates and clay, as well as the content of Fed in the Caragana microphylla plot. Thus, the stability of aggregates is reduced, which may be detrimental to the retention of organic carbon. This study provides theoretical knowledge for the stability theory of aggregates and the dynamic change of the organic carbon pool in this region.

      • 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.

      • 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

        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 sample plots 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, and some plots were relatively relatively Firmicutes. The abundance is up to 85%; fungi Ascomycota and Basidiomycota are the dominant 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) and available phosphorus (AP) 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.

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

        Yan Shuxian, LiuMing, LiuCaixia, ZhaoMengli, QiuWei, GuJiayue, FengGelin, GaoJing, CaiLingxiao, XuQiufang

        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.

      • 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.

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

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

        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.

      • 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 Land Use Change on Evapotranspiration in The Loess Tableland

        LU Yunqing, XIANG Wei, LI Min, SI Bingcheng

        DOI: 10.11766/trxb202103150143

        Abstract:

        【Objective】 Studying the response of evapotranspiration to land use change in Chinese Loess Plateau (CLP) is of great significance to clarify the effects of the Grain for Green Project on regional climate. Many studies have focused on the temporal trend or spatial distribution of reference evapotranspiration based on meteorological or satellite data at the watershed or regional scales. However, these studies cannot reflect the actual situation of the impact of land use change on surface evapotranspiration. Thus, the quantitative evaluation of actual evapotranspiration at the stand scale is lacking. Therefore, the objective of this study is to evaluate the effects of conversion from cultivated farmland into apple orchard on the actual evapotranspiration. 【Method】 A paired experimental study was conducted at the Changwu Tableland, south of the CLP. Both the cultivated farmlands and 20-year-old apple orchards were sampled with a soil auger (0.06 m in diameter) at 0.2 m intervals at each of the five selected sites, with a total of 10 deep soil cores (10 m). The volumetric soil water content was calculated by mass water content and soil bulk density, and the chloride concentrations of soil water were measured by extraction method. Since the local apple orchards were all converted from cultivated farmlands and the soil texture is uniform, the space-for-time method was applied. As precipitation is the only source of water for local crops, the chlorine mass balance method can be used to estimate groundwater recharge. Therefore, the surface evapotranspiration can be estimated by combining soil water mass balance with chloride mass balance. 【Result】 The results show that the averaged soil water content of 4~10 m soil layer in 20-year-old apple orchard was 0.20 m3 m-3. This was significantly lower than that in farmland (0.28 m3·m-3) and implies that soil water content were obviously affected by deep root after cultivated farmland converted into apple orchard 20 years ago. The long-term averaged groundwater recharge rate was 57±13.5 mm·a-1 in cultivated farmlands, which resulted in the actual evapotranspiration of 527±13.5 mm·a-1 and accounting for 90±2.3% of the annual precipitation. After cultivated farmland converted into 20-year-old apple orchard, the actual evapotranspiration significantly increased, with an average of 625 mm·a-1, accounting for 107% of the annual precipitation. Compared to cultivated farmlands, the actual evapotranspiration, in total, increased 1960 mm in 20-year-old apple orchard from 20 years ago, with an annual average of 98 mm. Within the 20-year-old apple orchards, soil water in 4~10 m, and 10~18 m soil layers contribute 24 mm·a-1 (4%), and 41 mm·a-1 (3%) to the annual evapotranspiration, respectively. 【Conclusion】 The small contributions of 4~10 m and 10~18 m soil layers indicated that the deep soil water (below 4 m) has an important role in evapotranspiration of the deep rooted apple tree. However, the main water sources for evapotranspiration still depend on the shallow soil water (0~4 m) that is easily recharged by the latest precipitation. This is the first study that quantitatively evaluated the impacts of cultivated farmland being converted into apple orchard on the evapotranspiration and the contribution of deep soil water to evapotranspiration. This study provides a scientific basis for evaluating the effects of land use change on the regional evapotranspiration and climate on the CLP and other regions with a significant land use/cover change.

      • 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.

      • Response of paddy soil anammox bacteria to rice straw returning and different tillage practices

        Sun Mei, Nie San An, Long Ze Dong, Li Chao, Wang Hua, Xiao Xiao Ping, Luo Zun Chang, sungeng

        DOI: 10.11766/trxb202109010267

        Abstract:

        【Objective】This study was carried out to reveal the response of paddy soil anammox bacterial activity, abundance and community structure to rice straw returning and different tillage practices, which may provide scientific basis for nitrogen (N) management of paddy field. 【Method】Three different till treatments (conventional till, rotary till and no till)+rice straw returning were set up, respectively, with conventional till but 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 significant difference and the values could be ranked as no till > rotary till > conventional till (p<0.05), while no significant difference was observed between control and rotary tillage+rice straw. No significant difference was detected in 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 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 no 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 potentially.

      • 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.

      • Effects of Humic Acid on Biodegradation of Pyrene by Mycobacterium sp. NJS-1

        fang wenwen, Li Xiaoning, wu shixi, wang fang, gu zhenggui, zhang yinping

        DOI: 10.11766/trxb202110010341

        Abstract:

        【Objective】Pollution by Polycyclic Aromatic Hydrocarbons (PAHs) in the soil environment has become a serious problem. In recent years, microbial degradation of PAHs to achieve soil remediation has become an important method. However, microbial degradation is not a very efficient and ideal process for the remediation of PAHs-polluted environments. In this study, humic acid (HA) was added during the degradation process to explore its effect on the microbial degradation of PAHs. 【Method】 Using pyrene as a typical PAH and HA as representative dissolved organic matter, Mycobacterium sp. NJS-1 with high pyrene degradation efficiency was selected to degrade pyrene with or without HA. Fourier transform cyclotron resonance mass spectrometry (FT-ICR-MS), laser confocal microscopy (CLSM), and techniques such as infrared and Raman spectroscopies were used to analyze the residual characteristics of pyrene, intermediates and colony changes during degradation. 【Results】 Results show: (1) The presence of HA significantly accelerated pyrene biodegradation. Approximately 88.33%±3.40% of pyrene was biodegraded within 7 days of incubation with the addition of HA, but only 35.33%±3.27% was biodegraded without HA; (2) The FT-ICR-MS results indicated that addition of HA induced two biodegradation pathways - attacking of 1,2-positions and 4,5-positions of pyrene by dioxygenase, whereas in the absence of HA only the 4,5-position was attacked; (3) The CLSM results showed that HA enhanced the growth of Mycobacterium sp. NJS-1 with no death of bacteria cells. Simultaneously, tyrosine proteins and fulvic acid-like compounds under visible light were detected and showed that HA enhanced bacterial activity by biofilm formation; (4) The results of the spectral analysis showed that a series of bands, mainly including protein amide, tyrosine, tryptophan and phenylalanine, red-shifted, implying that the interacted forces from the functional groups of bacterial surfaces changed in the presence of HA.【Conclusion】 HA can improve the degradation efficiency by increasing the degradation pathway of pyrene and inducing the interaction of functional groups on the cell surface to form a microbial membrane. Meanwhile, the addition of exogenous HA could also promote the interactions among colonies and accelerate the degradation. Keywords: Humic acid; Pyrene; Biodegradable; Microbial film

      • 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.

      • Impacts of Artificial Revegetation on Soil Fungal Community in Desertified Alpine Grassland

        wangyani, huyigang, wangzengru, liyikang, zhangzhenhua, zhouhuakun

        DOI: 10.11766/trxb202107050329

        Abstract:

        Abstract:【Objective】 This study aimed to illustrate the impacts of different revegetation approaches on the resilience of soil fungal communities in desertified alpine grasslands, and to explore the main environmental factors in driving the succession of soil fungal community.【Methods】We sampled surface soils within 0-10 cm from four different types of alpine grasslands, i.e., natural grassland (NG), desertified grassland (DG), herb-based artificial grassland (AG) and shrub-based artificial grassland (AS). Fungal community biomass, α-diversity and structure were studied using qPCR and Illumina Mesiq high-throughput sequencing technologies.【Result】1) grassland desertification significantly decreased soil fungal biomass and α-diversity, which showed no significant difference among AG, AS and NG after 22-year revegetation. 2) Both desertification and artificial revegetation significantly changed the fungal community structure. The relative abundance of Basidiomycota significantly (P<0.05) decreased after desertification. Some rare fungi phyla with less than 1% relative abundance tended to disappear, while the relative abundance of unclassified fungal phyla significantly (P<0.01) increased. After 22 years of revegetation, there was no significant difference in the relative abundance of most fungal phyla among AG, AS and NG. AG and NG showed more similar fungal structure than that of AS and NG. 3) The correlations of soil fungal α-diversity with vegetation and soil properties were diversity-index-dependent, while fungal structure significantly (P<0.01) positively correlated with most of vegetation and soil properties. Importantly, vegetation and soil properties jointly explained 21.4%-50.0% of variations in soil fungal community structure.【Conclusion】These findings indicate that fungal diversity and biomass in desertified grassland almost paralleled to the undegraded level after 22 years of revegetation. Despite fungal community structure in revegetation sites was still not similar to that of natural grassland, it is more beneficial to use grassland plants than shrub species for the restoration of soil fungal community structure in the degraded alpine grassland.

      • 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.

      • 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

        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.

      • Effects of Different Fertility Improvement Measures on Microbial Community Structures in Biological Red Soil Crusts of Woodland

        Wang Jinping, Haung Rongzhen, Zhu Liqin, Huang Guomin, Zhou Xianhua, Guan Hongzhi, Lin Lijing, Li Xin

        DOI: 10.11766/trxb202108130311

        Abstract:

        【Objective】Microorganisms play an important role in the formation of biological soil crusts while biological soil crusts are important for controlling soil erosion. However, there is limited research on microbial community in the biological soil crusts of southern red soil. Therefore, the changes of microbial community structure under forest fertility improvement measures in this area are unclear.【Method】The present study was conducted in the Pinus elliotti forest of tropical Quaternary laterite in the middle subtropical zone. Organic fertilizer, biochar, and lime + microbial fertilizer were added to soil, and bare land was set as the control (CK). High throughput sequencing technology (Illumina MiSeq) was used to study the effects of the three fertility improvement measures on bacterial and fungal community structures. 【Result】Results showed that 21 bacteriophyta and 7 mycobionta were detected in biological soil crusts. The dominant bacteriophyta were Acidobacteria (27.39%), Proteobacteria (25.90%), Actinobacteria (16.68%), Chloroflexi (12.26%), while the dominant mycobionta were Basidiomycota (61.19%) and Ascomycota (29.48%). The three fertility improvement measures had no significant effects on the diversities of bacteria and fungi, but significantly changed their community structures in order of organic fertilizer > biochar > lime + microbial fertilizer, and these effects were higher in bacteria, compared to fungi. Also, the effects of the three fertility improvement measures on specific bacteriophyta and mycobionta were different. The three fertility improvement measures increased the relative abundance of Proteobacteria, and decreased the relative abundance of Chloroflexi. Organic fertilizer and lime + microbial fertilizer increased the relative abundance of Ascomycota, but decreased the relative abundance of Basidiomycota, while biochar had opposite effects on mycobionta. Among the soil environmental factors, pH, organic carbon, and total nitrogen had a great influence on microbial community structure.【Conclusion】These results provided significant scientific guidance for the regulation of soil microbial community structures in biological soil crusts, which is beneficial for the formation of biological soil crusts and the control of water and soil erosion in southern red soil.

      • 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.

      • 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

        DOI: 10.11766/trxb202101110019

        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 93.98kg·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 ofin 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 31.44%. Thus, rReduced nitrogen fertilization could, therefore, 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.

      • 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

        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.

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

        YUAN Jinhua, QIAO Wandekua, E Shengzhe, CHE Zongxian

        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.

      • 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.

      • Metastable Equilibrium Adsorption of Alkali Metal Ions on the Surface of Montmorillonite and Its Specific Effects

        DU Wei, HU Feinan, XU Chenyang, LI Xiong, Lü Jialong

        DOI: 10.11766/trxb202105210265

        Abstract:

        【Objective】Metastable equilibrium is an important theoretical paradigm to describe the characteristics and extent of the actual reaction equilibrium in ion-exchange adsorption. This study aimed to theoretically derive the metastable equilibrium model of ion adsorption, establish the mathematical relationship between ion equilibrium adsorption amount and activation energy, and discuss the specific effect of alkali metal ion metastable equilibrium adsorption. 【Method】Using miscible displacement technology combined with the ion adsorption kinetic model and based on surface electrostatic field theory, the metastable equilibrium adsorption of K+, Na+, and Li+ on the surface of saturated Cs+-montmorillonite was investigated. The theoretical model was verified by carrying out adsorption kinetics experiments of K+, Na+, and Li+ on the Cs+-montmorillonite surface. 【Result】(1) Significant metastable equilibrium characteristics were observed during K+, Na+, and Li+ adsorption onto the surface of Cs+-montmorillonite saturated samples, and the adsorption activation energy (energy barrier) of exchange ions came from the desorption process of adsorbed Cs+; (2) Strong ion polarization caused by the surface electrostatic field resulted in specific effect of metastable equilibrium adsorption of each ion under the same ion concentration condition; (3) The metastable equilibrium of ion adsorption was affected by both ion concentration and specific ion effects, and the ion equilibrium adsorption capacity was proportional to the ion adsorption rate. 【Conclusion】The adsorption equilibrium of alkali metal ion at the montmorillonite surface is a metastable equilibrium rather than a real equilibrium. The presence of ionic metastable adsorption equilibrium should be attributed to the restraint of activation energies to ion adsorption kinetics. Also, the different polarization effects of alkali metal ions lead to different activation energies of each system, which further triggers the specific effect of ion metastable equilibrium adsorption.

      • High-resolution Digital Mapping of Soil Organic Carbon at Small Watershed Scale Using Landform Element Classification and Assisted Remote Sensing Information

        WEI Yuchen, LU Xiaoli, ZHU Changda, ZHANG Xiuxiu, PAN Jianjun

        DOI: 10.11766/trxb202103120140

        Abstract:

        【Objective】 Soil organic carbon (SOC) is an important indicator of soil fertility and plays a fundamental role in the terrestrial ecosystem carbon cycle. As one of the primary environmental factors in digital soil mapping (DSM), landform elements are irreplaceable in predicting SOC. The purpose of this study was to simulate the complex and nonlinear relationship between SOC and environmental variables and evaluate the importance of each variable to accuracy in SOC mapping. 【Method】We applied machine learning techniques to map SOC content in a small watershed (1: 25000) of Huangmei Town, Jurong City using high-resolution landform elements classification maps known as geomorphons, digital elevation model (DEM) derivatives, optical and synthetic aperture radar (SAR) remote sensing data. The performance of all geomorphon (GM) variables under different hyperparameter settings was evaluated to predict SOC content. Three machine-learners including bagged classification and regression tree (Bagged CART), random forest (RF) and Cubist were used to construct predictive models of SOC content based on 74 soil samples and different combinations of environmental covariates. Model A, Model B, and Model D included only GM variables, DEM derivatives, and remote sensing variables, respectively. Model B was a combination of GM data and DEM derivatives, while Model E included all predictor variables. The performance of these models was evaluated based on a 10-fold cross-validation method by four statistical indicators. Concordance index (C index), root mean square errors (RMSE), bias and coefficient of determination (R2) of the three models were worked out for evaluation of the accuracy of their predictions. The best model was screening-out for mapping SOC in the study area based on the raster datasets of all environmental variables. 【Result】Overall, the Cubist model performed better than RF and Bagged CART, and these models yielded similar spatial distribution patterns of SOC, i.e. an ascending trend from the northern hilly area to the southern flatter land of the study area. Our results showed that more accurate predictions of SOC content were provided with the introduction of GM variables than individual DEM derivatives. The GM map with 20 cells search radius (L) and 5° flatness threshold (t) showed the highest relative importance within four GM variables in three models. The Cubist E model that functioned based on GM landform elements classification variables, DEM derivatives and remote sensing variables was much better than the others in performance and could explain most of the spatial heterogeneity of SOC (R2 = 0.53). Also, the prediction accuracy changed with and without the GM predictors with the R2 for estimating SOC content using the Cubist model increasing by 14.3%. The SOC contents of the hilly region predicted with the Cubist E model ranged from 5.65 to 13.31 g·kg-1. In addition, topographic variables were the main explanatory variables for SOC predictions and the multi-resolution index of valley bottom flatness (MRVBF) and elevation were assigned as the two most important variables. 【Conclusion】The Cubist model that functions based on GM variables, DEM derivatives, as well as remote sensing variables, is a promising approach to predicting the spatial distribution of SOC in hilly regions at a small watershed scale. The results of this study illustrate the potential of GM landform elements classification data as input when developing SOC prediction models.

      • 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 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

        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 g?cm-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.

      • 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 Progresses on Soil Enzymes as Indicators of Soil Health and Their Responses to Heavy Metal Pollution

        TAN Xiangping, HE Jinhong, GUO Zhiming, WANG Ziquan, NIE Yanxia, YE Qing, HE Wenxiang, SHEN Weijun

        DOI: 10.11766/trxb202107240275

        Abstract:

        Soil enzymes play a vital role in the biogeochemical cycling of key elements, maintenance of animal and plant health, and decontamination of environmental pollution. The activities of soil enzymes can be applied in the environmental risk assessment of soil heavy metal pollution. However, the effects of heavy metals on soil enzyme activities varied with soil physicochemical and biological properties and the differences of research methods. Thus, these factors hinder the application of soil enzymes in the assessment of soil health and quality. This study systematically elaborates the eco-toxicological effects of heavy metal pollution on soil enzyme activities and the kinetic characteristics of soil enzyme catalytic reactions. We also constructed a conceptual diagram of soil enzymes in response to soil-heavy metals-microorganisms, proposed and discussed the future trends and directions in soil enzyme in the assessment of heavy metal pollution. Soil enzymes are potential biological indexes for the evaluation of soil heavy metal pollution, because the determination of soil enzyme activity is efficient and cheap, and soil enzyme activity is sensitive to heavy metal toxicity. However, soil enzyme activity may overestimate or underestimate the ecological toxicity of heavy metals as an individual indicator. Furthermore, there is no uniform standard on how to select soil enzyme as a general indicator to assess the toxicity of heavy metals in different soils. Also, it is difficult to establish a quantitative relationship between the ecological doses of heavy metals for soil enzyme activity and soil properties, which led to the arguments about its accuracy and applicability in the ecological risk of heavy metal pollution. Therefore, it is crucial to use new technologies and methods to uncover the reactive mechanisms of enzymes to heavy metal toxicity in different types of soils, and quantitatively analyze the relationship between soil properties and ecological doses of heavy metals based on kinetic parameters. This can strengthen the practical application of soil enzymes in the diagnosis of soil pollution by heavy metals.

      • Nitrate-Dependent and Photosynthetic Fe(II) Oxidation Processes in a Calcareous Paddy Soil

        CHEN Zhihuai, WANG Xugang, SUN Lirong, DONG Leheng, GUO Dayong, SHI Zhaoyong

        DOI: 10.11766/trxb202104010174

        Abstract:

        【Objective】Iron redox processes under anaerobic conditions are closely correlated to nitrogen cycling in soils. Both nitrate-dependent ferrous oxidation (NDFO) and photosynthetic ferrous oxidation (PFO) are crucial pathways of biological ferrous iron oxidation. However, whether NDFO occurs in calcareous paddy soils and its relation to PFO is still ambiguous. 【Method】 We collected soil samples from Mengjin County, Henan Province, within the middle and lower reaches of the Yellow River. The soil samples were made into slurries using 10 mmol?L-1 NO3-/NH4+ solution or water at the very beginning. Then the slurries were anaerobically incubated under darkness or illuminated. On the 7th day of the incubation, we injected 0.5 mL 70 mmol?L-1 NO3- or NH4+ into a part of those slurries made with water to adjust their external NO3- or NH4+ content to 10 mmol L-1. To assess the iron reduction, and ferrous oxidation, Fe(II) in the slurries was measured dynamically using the phenanthroline colorimetric method. To evaluate the nitrogen transformation, NO3- and NO2- were analyzed dynamically using an ion chromatograph equipped with an electrical conductivity detector, and NH4+ was measured after the incubation by 1 mol?L-1 KCl extraction-Kjeldahl method. To fractionate the PFO, O2 in the headspaces was determined dynamically using a portable fiber-optic trace oxygen meter. 【Result】The results showed that, though no apparent ferrous oxidation was observed, iron reduction rate decreased by 0.28 mg?g-1?d-1 and 0.33 mg?g-1?d-1. Also, the iron reduction rate constant was decreased by 0.15 d-1, and 0.17 d-1 in slurries under darkness with NO3- or NH4+ amended at the very beginning. Ferrous iron was oxidized by 2.21 mg?g-1 and 0.68 mg?g-1 in slurries with NO3- or NH4+ injected on the 7th day of the dark incubation and by 1.99 mg?g-1 in slurries incubated under light. In addition, Fe(II) in the slurries was negatively correlated to O2 in the headspace. Importantly, the reduction of NO3— to NH4+ occurred in the slurries with NO3- injected on the 7th day of dark incubation. 【Conclusion】 Ferrous oxidation caused by NDFO was observed in the calcareous paddy soil amended with 10 mmol?L-1 NO3- and incubated anaerobically under darkness. However, the oxidation could be inhibited since the ferric iron resulting from NDFO would be reduced rapidly when the NO3- becomes depleted. Both NDFO and PFO occurred in the calcareous paddy soil incubated under illumination and the PFO resulted in 1.99 mg?g-1 ferrous iron oxidized. Ferrous oxidation in soils under illumination was increased by 0.57 mg?g-1 when NO3- was injected. These results help to further understand the redox processes and the coupled nitrogen transformation in wetland soils.

      • Effects of Straw returning instead of Chemical Fertilizer on Crop Yield and Soil Fertility in Fluvo-aquic Soil

        ZHAO JinHua, CHEN Lin, Duan Yan, Zhang Congzhi, Ma Donghao, ZHANG JiaBao

        DOI: 10.11766/trxb202106230326

        Abstract:

        Abstract:【Objective】The excessive application of chemical fertilizers in China’s major grain-producing areas has led to a series of problems including the reduction of fertilizer utilization rate, soil quality degradation, and increase pollution risk,【Method】A field experiment was set up in the fluvo-aquic soil area of the Huang-Huai-Hai Plain to study the effects of straw returning combined with different proportions of nitrogen and phosphorus reduction on soil nutrients. Also, the effects of these amendments on crop yields, straw nutrient release, and soil microorganisms were studied to clarify the nutrient components of chemical fertilizers that can be replaced by straw returning without loss of crop yields and soil nutrients. Importantly, the microbial mechanism that promotes efficient utilization of straw nutrients and provides a basis for the implementation of chemical fertilizer reduction action was explored.【Result】The results showed that compared with conventional fertilization, a 30% reduction of nitrogen or 50% reduction of phosphorus had no significant effect on crop yield and soil nutrient content. The straw degradation rate reached 43.33% ~ 53.11% in the first season while the reduction of 30% nitrogen or 50% phosphorus could increase it by 12.40%, and the degradation rate reached 63.41% ~ 75.62% after two years. Nitrogen reduction by 100% significantly reduced the abundance, species richness and diversity of bacterial fungi, while phosphorus reduction had little effect. Nitrogen and phosphorus reductions by 30% and 50%, respectively, mainly increased the relative abundance of Gemmatimonadetes longimicrobiaceae and Proteobacteria nitrosomonadaceae in bacteria, increased the relative abundance of Chrytridiomycota GS13 class in fungi, and decreased the relative abundance of Ascomycota sordariomycetes and Mortierellomycota mortierellomycetes. Redundancy analysis showed that the main environmental factors affecting bacteria and fungi were soil organic carbon (SOC) and total nitrogen (TN). 【Conclusion】In conclusion, straw returning combined with nitrogen reduction by 30% or phosphorus reduction by 50% has the potential to maintain fertilizer use efficiency and stable yield in the medium and high yield fields of fluvo-aquic soil.

      • Status of Soil Phosphorus Pool and Environmental Risk Assessment in Rice-Oilseed rape Rotation Area in the Yangtze River Basin

        yanjinyao, guolixuan, wangkunkun, liaoshipeng, luzhifeng, congrihuan, lixiaokun, rentao, lujianwei

        DOI: 10.11766/trxb202108050327

        Abstract:

        The objective of this study was to clarify the status of soil phosphorus (P) pools in rice-oilseed rape rotation areas in the Yangtze River Basin, and assessed the risk of soil P leaching. Alse it aimed to provide a reference for reasonable phosphorus application in the rice-oilseed rape rotation system in the Yangtze River Basin. From April to May 2018, 247 soil samples of the cultivated layer after the oilseed rape harvest were collected in 14 provinces (cities/districts) around the Yangtze River Basin in typical rice-oilseed rape rotation regions to determine soil total phosphorus, available phosphorus (Olsen-P) and soluble phosphorus (CaCl2-P). With reference to soil total phosphorus and available phosphorus grading indexes, the current status of soil phosphorus abundance and deficiency in rice-oilseed rape rotation areas in the Yangtze River Basin was clarified, and the quantitative relationship between Olsen-P and CaCl2-P was established. According to the available phosphorus grading, 72 samples were selected for Hedley phosphorus fraction determination, and the distribution characteristics of soil phosphorus pool in rice-oilseed rape rotation were analyzed. The results showed that the average content of total phosphorus, available phosphorus and CaCl2-P in cultivated soils of rice-oilseed rape rotation area in the Yangtze River Basin were 0.62 g·kg-1, 23.2 mg·kg-1 and 0.49 mg·kg-1, respectively. There was no significant difference in total phosphorus between the upper, middle and lower reaches of the Yangtze River, and 48.6% of the total area was in a state of abundance. The lack and excess of soil available phosphorus coexist, accounting for 23.1% and 31.1%, respectively. The areas of soil available phosphorus deficiency and excess were concentrated in the middle and lower reaches of the Yangtze River, respectively. Also the soil phosphorus pool was dominated by inorganic phosphorus, accounting for an average of 82.2%. The average content of H2O-Pi, NaHCO3-Pi, NaOH-Pi, HCl-Pi, NaHCO3-Po, NaOH-Po and Residual-P pools were 10.8, 46.8, 115.6, 218.6, 22.3, 104.9 and 193.8 mg·kg-1, respectively. With an increase in soil available phosphorus levels, the contents of NaHCO3-Pi and NaOH-Pi increased significantly, and the stable phosphorus pools (HCl-Pi and Residual-P) were relatively stable. The relationship between Olsen-P and CaCl2-P conformed to the double-line model. When a change point appeard, the content of Olsen-P was 39.9 mg·kg-1 with a corresponding content of CaCl2-P of 0.6 mg·kg-1. Also, when the Olsen-P content was greater than 39.9 mg·kg-1, the risk of soil phosphorus leaching increased. Generally, the soil phosphorus content in the rice-oilseed rape rotation area in the Yangtze River Basin showed an upward trend and 13.0% of this area was at a high risk of phosphorus leaching. Also, the soil phosphorus mainly accumulated in stable phosphorus pools. Therefore, more attention should be paid to the rational application of phosphorus fertilizers, appropriately reduce phosphorus fertilizer input, and tap the potential of stable phosphorus pools in soils. Thus, this will reduce soil Olsen-P accumulation, environmental P loss in the rice-oilseed rape rotation system, and improve crop P fertilizer utilization.

      • 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

        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.

      • Research on the Cross-Coloration Effect of Iron Oxides and Humus in Soil

        GUAN Yanxia, LU Jinmei, MA Rongjun, XING Dengchun, LONG Xiaoyong

        DOI: 10.11766/trxb202103200154

        Abstract:

        Soil color is an important index of soil classification, climate reconstruction and environmental remote sensing. Iron oxides and humus are the two major chromogenic components of soil, which dominate the spectral response characteristics of soil. 【Objective】This paper is based on the unclear cross-coloration effect of iron oxides and humus in soils and sediments.【Method】 We selected kaolinite as substrate, hematite (Hm) and goethite (Gt) as the representatives of iron oxides, humic acid (Ha) and fulvic acid (Fa) as the representatives of humus. The spectral characteristics, color changes and cross-interference characteristics of iron oxides and humus with different contents were discussed by high-resolution Diffuse Reflectance Spectrum (DRS). 【Result】It is found that in terms of the chromogenic effect of a single component, Hm is stronger than Gt, and Ha is stronger than Fa. The addition of humus has an obvious effect on the coloration of iron oxides, which usually reduces the Mean Reflectance, Value (V) and Chroma (C), and makes the Hue (H) yellowish. The anti-jamming ability of Hm is greater than that of Gt. The a* of Lab color system and the redness of DRS are sensitive to the change of Hm content. The b* of Lab color system and the yellowness of DRS are sensitive to the change of Gt content. They can be used as indices for the quantitative determination of soil iron oxides. However, the addition of Ha can lead to the underestimation of Hm and Gt, and the addition of Fa has less effect on the estimation depending on the contents of Hm and Gt. 【Conclusion】Based on this, the estimation formulas of Hm and Gt mixed with different contents of humic acids are given. It not only helps understand the color change of natural soils but also lays a foundation for iron oxide determination at a large scale based on remote sensing.

      • 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.

      • Evaluation of Phosphate Fertilizer Reduction on Annual Phosphorus Loss under Intensive Open-field Vegetable Production

        WANG Rui, SHI Weiming, LI Yilin

        DOI: 10.11766/trxb202102050078

        Abstract:

        【Objective】Intensive vegetable fields have been the priority control projects for phosphorus (P) loss in farming due to massive fertilization and flood irrigation, accounting for the highest proportion of P pollution from farmlands. Therefore, (i) quantifying the assessment of the annual P loss of vegetable fields, (ii) clarifying the reasonable threshold range of phosphate fertilization for vegetables, and (iii) controlling P migration and loss from vegetable fields through the source are of great significance for effectively reducing the environmental pressure caused by agricultural non-point source pollution. 【Method】A plot experiment in the Tai Lake Basin with conventional fertilization and phosphate fertilization reduction treatments was conducted in a perennial and open vegetable field. The one-year vegetable rotation experiments focused on clarifying the environmental threshold of P and annual P runoff loss characteristics. There were five treatments, conventional fertilization (CK), reduction of 20% (P-20), 30% (P-30), 50% (P-50), and 100% (P-100) based on conventional P fertilization. 【Result】 The environmental threshold of soil P in the tested vegetable fields was 78.9 mg?kg-1. During the whole experimental period, Olsen-P content in the soil surface of different treatments exceeded the leaching threshold. The results of annual total P (TP) runoff loss concentration in vegetable fields showed that with the decrease of phosphate fertilization input, the annual loss concentration of TP decreased. Also, dissolved P (DP) was the dominant form of P species, accounting for 50.1%~63.1%. Runoff loss loads of P showed seasonal characteristics, with the amount of P loss in a summer-autumn season (1.93~3.26 kg?hm-2), accounting for 59.2%~63.2% of the annual P loss flux. Based on the structural equation modeling (SEM), the amount of phosphate fertilizer had a direct and extremely significant effect on TP loss concentration. Furthermore, TP loss concentration had a positive and extremely significant impact on TP runoff loss load with a path coefficient of 0.97. The loss coefficients of P were between 1.36% and 3.33%, and the lowest loss coefficient was in the P-50 treatment. With a decreased amount of P applied, the reduction ratio of P runoff loss increased, and a P loss reduction rate of 41.5% was recorded in the P-100 treatment. Treatments of P-20 and P-30 had no significant yield reduction during a three-successive vegetable growth period in a year compared with CK. 【Conclusion】 Taking environmental risk and economic yield into consideration, it is appropriate to reduce between 20%~30% P fertilizer application based on conventional phosphate fertilizer rate for open vegetable fields in Tai Lake region.

      • Effects of Different Phosphorus Application Techniques on Phosphorus Availability in a Rape System in a Red Soil

        WANG Yikun, CAI Zejiang, FENG Gu

        DOI: 10.11766/trxb202104210207

        Abstract:

        【Objective】Phosphorus (P) is an indispensable nutrient needed for plant growth and development and P is deficient, especially in the red soil region of South China. However, the unsuitable application of P fertilizer results in low use efficiency of the fertilizer, ranging from 10% to 25% in the current season in the region. This could result in P surpluses in soils, and runoffs and is one of the important nonpoint source pollutions of aquatic habitats and other water resources. Thus, it is important to investigate a suitable P fertilization in the region to improve P use efficiency and sustain crop yields. 【Method】A field experiment was conducted at the Experimental Station of the Chinese Academy of Agricultural Sciences, Qiyang, Hunan Province, China. The effects of different phosphorus fertilizers (superphosphate, swine manure, calcium magnesium phosphate, monoammonium phosphate, diammonium phosphate), P application rates (conventional phosphorus application, phosphorus reduction 20%, phosphorus reduction 30%), and P combined with amendments (lime, calcium magnesium phosphate fertilizer combined with diammonium phosphate, or crop straw return) on phosphorus availability and crop growth in red soil were tested. 【Result】Of the different phosphorus fertilizers, swine manure induced the highest soil available phosphorus and aboveground biomass and P use efficiency in 2019. Also, under this treatment the crop yield in 2020 was significantly higher than that of other treatments. Compared with the control treatment, swine manure treatment significantly increased soil available phosphorus and aboveground biomass by 32% and 241%, respectively, in 2019, and by 73% and 510% in 2020. As P application rates decreased, the soil available P content was also significantly decreased. However there were no changes in rape seed yield, aboveground biomass, P use efficiency and phosphorus agronomy efficiency. Among them, 30% phosphorus reduction was the best treatment. Compared with a single application of calcium magnesium phosphate, the combined application of calcium magnesium phosphate and diammonium phosphate effectively improved crop yield, soil available phosphorus and phosphorus efficiency index to a certain extent. The treatment of calcium magnesium phosphate fertilizer + diammonium phosphate had the best effect on the crop yield, soil available phosphorus, phosphorus fertilizer cumulative use efficiency, phosphorus agronomic efficiency and soil phosphorus surplus. The addition of lime improved crop yield, soil available phosphorus and phosphorus fertilizer cumulative use efficiency , but did not reach a significant level as compared to superphosphate only treatment. There was a significant positive correlation between rape seed yield and soil available phosphorus. 【Conclusion】 From the above research results, we can conclude that the replacement of chemical phosphorus fertilizer by swine manure phosphorus could achieve the purpose of reducing application and increasing efficiency. Also the best amount of phosphorus fertilizer was a 30% reduction of conventional phosphorus application rate. The calcium magnesium phosphorus fertilizer as a P source should be applied combination with diammonium phosphate to supply P demand for crop growth in such weak acidic red soils.

      • 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

        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,so 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.And 89.4% of the sloping farmland utilization in the province is planting crops, and maize and soybean are the main ones 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 provided a basis for the calculation of the soil-fixing ability of crop roots. It also provided a reference for the rational layout of crop planting to prevent soil erosion on slope farmland.【Method】In this study the field experiment was designed to have three treatments and a total of 9 experimental plots were set up, 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 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: ①Compared with rootless soil, the roots of maize and soybean could significantly enhance the shear strength of root-soil composite (P < 0.01), and the strength of the root-soil composites is increased by 117.65% and 71.91%, respectively;②The 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). and the contribution of fine roots with D≤1mm to the cohesive force increment is greater than that of other diameter-level roots;③In the different root architecture traits, the number of root branches of maize is 45.44% higher than that of soybeans, and the root distribution of each diameter class is more even. The corn root-soil complex shows weak strain hardening characteristics when the root content increases. The crack propagation slows down and the lateral deformation decreases.【Conclusion】The root systems of the two crops could enhance the shear strength of the soil, but the different root structure types have 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, so 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.

      • Enrichment Characteristics of Soil Ammonium Nitrogen in Ionic Rare Earth Mining Area

        XU Zhe, YANG Jinling, ZHANG Ganlin, ZHAO Yue, ZHOU Jun

        DOI: 10.11766/trxb202104140195

        Abstract:

        【Objective】The leaching agent (ammonium sulfate) causes residues of ammonium nitrogen in the soil of ionic rare earth mining area.This results in serious nitrogen pollution in the soil and water bodies and destroys the ecological environment in the mining area. It also endangers the health of the surrounding residents and restricts the mining of ionic rare earth ore. However, the ammonium nitrogen pollution situation in ionic rare earth tailings and its impact mechanism are still unclear. 【Method】In order to understand the enrichment characteristics of soil ammonium nitrogenin in the mining area and its influencing factors, we chose an in-situ leaching ionic rare earth mining area that has been closed for 4 years in Longnan County, Ganzhou City, Jiangxi Province. We sampled sites located on the different slopes of the hill. Soil samples were chosen from the soil surface to the bottom of the ore body, with a depth of 5.5 to 9.7 m. Ammonium nitrogenin and other soil properties in the soil were determined. 【Result】The results show that soil ammonium nitrogenin content in the mining area ranged from 2.32 to 1056.44 mg·kg-1, and was several times or even hundreds of times higher than in the natural and farmland soils. Ammonium nitrogenin in the mining layers with rare earth was higher than in the upper soil, and with wide the variations among different soil layers in the vertical direction. Also, soil ammonium nitrogenin content in the hill slope followed the sequence of top > bottom > middle slope. The correlation between soil ammonium nitrogen and the physicochemical properties of ionic rare earth tailings was observed to be different from the research conclusions of natural or farmland soil. Due to the supersaturation of ammonium in the soil, the distribution of ammonium nitrogenin is not directly controlled by soil basic physicochemical properties which have an important influence on the ammonium nitrogen adsorption, such as soil clay, cation exchange capacity, etc. 【Conclusion】The major factors observed to influence ammonium nitrogen are the depth and amount of leaching solution inputting, and the permeability changes caused by the soil structure. Mining facilities such as leaching liquid pools, liquid collecting ditch, etc, affect the surrounding soil ammonium nitrogenin content. Due to gravity, ammonium nitrogen will gradually migrates from the top to the middle and the bottom of the slope. This causes ammonium nitrogen to accumulate at the bottom of the slope over time. Under the leaching action of rainfall, a large amount of ammonium nitrogenin in mining area soil will continuously migrate to the surrounding soil and water, which will harm the ecological environment in the long run. The results of this study are of great significance for improving the migration process of soil nitrogen in ionic rare earth mining areas and guiding the treatment of ammonia nitrogen pollution.

      • Effects of Freeze-thaw Cycles and Soil Water Contents on Disintegration Characteristics of Brown Earth

        ZHU Longxiang, FAN Haoming, MA Renming

        DOI: 10.11766/trxb 202103020119

        Abstract:

        【Objective】 Undisturbed brown earth soils from 5~7 cm and 25~27 cm depths in the Shenyang area of China were collected for this research. The effects of freeze-thaw cycles and soil water contents on the disintegration characteristics of the soils were analyzed. 【Method】 Based on meteorological data and field observation, five freeze-thaw cycles were designed. The weighed water contents of the soil samples were regulated to 10%, 15%, 20%, 25% and 35%, respectively, and the disintegration process was measured. 【Result】 1) The soil disintegration had four phases, including the rapid water absorption phase, exponential disintegration phase, step disintegration phase, and disintegration completion phase. In the four phases, the exponential disintegration phase was regarded as the main disintegration process. Importantly, during the exponential disintegration phase, the soil sample collapsed continuously due to pulling or losing support. Also, the disintegration rate in the exponential disintegration phase and non-capillary water content showed similar behavior as the increasing freeze-thaw cycle. According to the two fitting surfaces, there was a most easily disintegrating soil water content in the range10%~15% in which the total disintegration rate was largest. When the water contents were 25% and 35%, all soil samples skipped the exponential disintegration phase and directly entered the step disintegration phase. The total disintegrations of 5~7 cm and 25~27 cm soils were very small under 35% soil water content, and was no more than 6.93% and 11.14%, respectively. 2) Over-consolidation was observed on soil samples with 10% and 15% water contents, and the polarization distribution of soil pores was accelerated under the freeze-thaw cycles. The disintegration rate of the exponential disintegration phase and non-capillary water content of both soil samples was increased after continuous freeze-thaw cycles. Under the freeze-thaw cycles, the structure of soil samples with 25% and 35% water contents was destroyed, soil pores were expanded with an internal settlement, and the water absorption capacity was reduced. 3) The pore difference of 25~27 cm soil sample was slightly larger, the control ability of electric double layer to free water was inhibited by the higher clay content, which resulted in a higher total disintegration rate. 【Conclusion】 The ability of soil to resist erosion from inside to outside was transformed into the ability from outside to inside under freeze-thaw cycles. All the findings may serve as a data basis for brown earth soil erosion research.

      • Research Progress of the Evolution Trends and Controls of Soil Organic Phosphorus Speciation during Natural Pedogenesis Based on Solution 31P Nuclear Magnetic Resonance

        LUO Yuanjun, HUANG Laiming, YUAN Dagang

        DOI: 10.11766/trxb202105060240

        Abstract:

        Soil organic phosphorus (Po) is an important phosphorus pool in soils. The forms, contents and bioavailability of Po change significantly with pedogenesis, which affects soil P supply, nutrient balance and ecosystem productivity. However, compared with inorganic phosphorus (Pi), previous studies paid less attention to Po, which was mainly attributed to the difficulty in the extraction, analysis and identification of different Po speciation. In recent years, the solution 31P nuclear magnetic resonance (31P NMR) spectroscopy was increasingly applied in pedology for characterizing Po compounds, providing a new way for quantitative analysis of Po forms and contents. This significantly improved our understanding of the transformation process of Po during long-term terrestrial ecosystem evolution. This paper systematically summarized the forms and properties of soil Po, and described the principle and procedures of solution 31P NMR spectroscopy for characterizing soil Po speciation. Then we reviewed the evolution trends and controls of different Po speciation during natural pedogenesis, and put forward several questions that need to be resolved in the future. Future research priorities include (i) determining the rates, pathways and thresholds of soil Po transformation during long-term soil evolution; (ii) elucidating the coupling relationship between Po and other nutrients such as C and N at different stages of soil evolution and the mechanisms of fixation and release of soil Po; and (iii) building a quantitative model of Po evolution in different types of soils. Providing solutions to the above questions can improve our understanding of the phosphorus biogeochemical cycle in Earth’s Critical Zone and provide a theoretical basis for nutrient management and regulation at different stages of soil evolution, and would promote sustainable utilization of soil resources.

      • 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

        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.

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

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

        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.

      • Effects of Different Treatments with Straw Returning on Arbuscular Mycorrhizal Fungal Community and Corn Phosphorus Utilization Efficiency

        HU Kaijie, LUAN Lu, ZHENG Jie, LI Jing, XUE Jingrong, SUN Bo, JIANG Yuji

        DOI: 10.11766/trxb202103280167

        Abstract:

        【Objective】Arbuscular mycorrhizal fungi (AMF) can form a symbiotic structure with 80% of plants, and play important roles in the nutrient cycling of the plant-soil system. As a typical soil in south China, red soils are facing numerous challenges including rapid acidification, low phosphorus availability, and the degradation of soil microbiome functioning. Straw returning has been proposed as an effective method to improve the fertility of red soils. In order to improve and control the degradation of red soil, we studied the effect of the AMF community in the rhizosphere on corn phosphorus utilization efficiency in a typical red soil.【Method】In this study, we performed a long-term field experiment by returning straw with equal carbon content in the Red Soil Agroecosystem Experiment Station of the Chinese Academy of Sciences in Yingtan, Jiangxi Province. Five fertilization treatments were set up, including no fertilization (CK), conventional NPK (N), NPK with straw (NS), NPK with straw and pig manure (NSM), and NPK with straw biochar (NB). High-throughput sequencing was used to estimate the diversity and structure of the rhizosphere AMF community in driving plant growth and phosphorus utilization efficiency under the different treatments.【Result】The results showed that soil properties were significantly affected after treatments with straw. The NSM treatment increased significantly the contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP), as well as the acid phosphomonoesterase (ACP) and alkaline phosphomonoesterase (ALP) activities. Treatments with straw significantly promoted the diversity and modified the structure of the rhizosphere AMF community. Glomus and Paraglomus were the two dominant genera in the AMF community. The diversity and structure of the AMF community were mainly affected by SOC. Corn yield and phosphorus utilization efficiency were the highest under the NSM treatment. Also, phosphate utilization efficiency was primarily affected by AP, TP, SOC, TN, the diversity and composition of the AMF community, and ACP activity.【Conclusion】The composition of the AMF community in the rhizosphere may regulate the phosphorus activation, corn productivity, and phosphorus utilization efficiency under all three treatments with straw. Our results highlight the importance of the rhizosphere AMF community in strengthening soil health and crop productivity.

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

        TIAN Yuhua, YIN Bin, ZENG Ke, ZHAO Xu

        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.

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

        HUANG Minxue, GUAN Yufeng, SU Zixian

        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.

      • Characteristics of Enhanced Microbial Thermogenic Functions in Hyperthermophilic Composting

        CUI Peng, AI Chaofan, LIAO Hanpeng, ZHOU Shungui

        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 80oC 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 70oC, 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.

      • 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

        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.

      • 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

        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 correlation 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.

      • Soil nitrogen supply and retention capacity determine the effect and utilization rate of nitrogen fertilizer in paddy field.

        Yang Binggeng, Cai Siyuan, Liu Yujuan, Xu Lingying, Wang Yu, Peng Xianlong, Zhaoxu, Yan Xiaoyuan

        DOI: 10.11766/trxb202104070181

        Abstract:

        Wuchang and Changshu are the representative production areas of high-quality japonica single-cropping rice in Northeast and East of China, respectively. However, the amount of nitrogen (N) fertilizer required to maintain a high yield in Wuchang is usually much lower than that in Changshu, but the agronomic use efficiency of fertilizer N (AE) is higher than that in Changshu. Different hydrothermal conditions, crop varieties, farmland managements and soil types in these two places make it difficult to identify what causes such regional differences. To explore soil factors" influence on NUE, black paddy soil (BS) and gleyed paddy soil (WS) were collected from the two rice fields. There were three N treatments as follows: no N treatment (CK), low N rate and high N rate (150 and 300 kg N·hm-2 with 15N urea). A rice pot experiment was carried out in Changshu National Agro-Ecosystem Observation and Research Station to compare the rice yield, NUE, and total N loss between the two soils. The characteristics of N mineralization in the two paddy soils were also studied through a three-week indoor anaerobic incubation experiment. The results suggested that the rice yield, agronomic fertilizer N use efficiency and above-ground N uptake of BS were better than that of WS among these N treatments under the same climate, rice variety and management levels. The NUE of BS was higher than that of WS by about 20.0-28.7%. However, the 15N recovery efficiency of BS was only higher than that of WS by about 5.56-8.01%. Although the above-ground N uptake by rice increased after N addition in two soils, the N increment of BS from the soil source was 95%-215% higher than that of WS. Also, the increment of N taken up from the priming effect (difference of above-ground plant N uptake derived from the soil between CK and the corresponding N application treatments) of BS was 173-354 mg·pot-1 and 88-113 mg·pot-1 for WS. This observation was consistent with the results that the net soil N mineralization amount of BS was 0.95-2.49 times higher than that of WS after N application in the anaerobic incubation experiment. Thus, this result indicated that the N application had a greater priming effect on the increase of N supply in BS soil. Also, the total loss of 15N fertilizer in WS soil was significantly higher than that of BS with the increase of N application rate in the pot experiment. Overall, the high yield and NUE of BS may be related to the fact that N fertilizer could provide a greater priming effect and maintain a higher soil N retention level. However, the rice yield of WS depended more on the N fertilizer input due to its lower priming effect of N fertilizer and had a weaker ability to retain fertilizer N. Thus, the soil is an important factor influencing the difference in agronomic use efficiency of fertilizer N and N use efficiency in paddy fields.

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

        ZHU Yanjie, HEYan, XU Jianming

        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.

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

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

        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.

      • Low pH Stress Induces the Accumulation of ROS By Increasing Production of Nitrate Reductase-Dependent NO in Rice Root Tips

        SUN Liming, MA Jianfeng, SHEN Renfang

        DOI: 10.11766/trxb202102070085

        Abstract:

        【Objective】 Low pH stress is one of the major factors limiting crop production on acidic soils. It often coexists with metal ion toxicity and this makes it difficult to explore directly the effect of pH in acidic soils. So far, the mechanisms of low pH stress in rice is poorly understood. 【Method】Two rice varieties with different low pH tolerance, Kasalath (low pH-tolerant) and Jinguoyin (low pH-sensitive), were selected to (i) study the relationship between low pH stress and the accumulation of nitric oxide (NO) and reactive oxygen species (ROS), and (ii) explore the regulatory relationship between NO and ROS under low pH stress. 【Result】Low pH caused the accumulation of NO and ROS in the root tips of Jinguoyin, but there was no significant change in Kasalath. The NO scavenger cPTIO reduced NO and ROS accumulation in root tips of Jinguoyin. Feedback inhibitor of nitrate reductase Gln significantly reduced NO content in the root tips of Jinguoyin under low pH, while L-NAME, a nitric oxide synthase inhibitor, did not affect NO content in the root tips of Jinguoyin. Low pH significantly increased the expression of nitrate reductase genes NIA1, NIA2 and NIA3 in Jinguoyin, and also increased the activity of nitrate reductase.【Conclusion】Low pH stress of Jinguoyin was related to the NO-mediated ROS accumulation. The NO signal generated under low pH stress is mainly synthesized by nitrate reductase through increasing the expression of NIA1 and NIA2.

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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