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    Insights and Perspectives
    • Nitrogen Fertilizer Demand in China in the Context of Green Development

      LI Tingyu, YAO Lan, ZHONG Yuxiu, WANG Yi, LI Weifang, XU Yang, LI Dongjia, LIU Rui, LI Bei, ZHANG Weifeng

      2025,62(2):308-321, DOI: 10.11766/trxb202405280211

      Abstract(319) HTML(415) PDF(718.77 K)( 420) Collect

      Abstract:

      Nitrogen fertilizer is essential for food security, but its excessive application leads to reactive nitrogen emissions, causing severe environmental issues. In the new era of promoting green development, clarifying China's reasonable nitrogen fertilizer demand and pathways for reducing chemical nitrogen fertilizer is crucial for agricultural transformation and upgrading. This study comprehensively analyzes the yield potential and nitrogen demand of 31 major crops in China and determines the reasonable nitrogen fertilizer demand under the conditions of food security and ecological sustainability by combining the nitrogen surplus levels under optimized management for different crops. Under the green development framework, the total reasonable nitrogen nutrient demand in China is 31 million tons, with a reasonable chemical nitrogen fertilizer demand of 19.04 million tons, accounting for 61% of the total demand. Future pathways for rational nitrogen fertilizer application in China should consider nitrogen fertilizer quota, increasing organic nutrient input and substitution ratio, increasing the planting proportion of leguminous crops to enhance biological nitrogen fixation potential, and optimizing nitrogen fertilizer product structure. Under these pathways, the potential for reducing chemical nitrogen fertilizer ranges from 26% to 53%. Specifically, under reasonable nitrogen input conditions (nitrogen quota), increasing the organic nutrient substitution ratio to 40% could lower the chemical nitrogen fertilizer demand to 14.28 million tons, with a reduction potential of 44%. Further increasing the planting area of leguminous crops (enhancing soybean-maize rotation ratio) could reduce the chemical nitrogen fertilizer demand to 13.6 million tons, with a reduction potential of 47%. Finally, optimizing the nitrogen fertilizer product structure could further reduce the reasonable chemical nitrogen fertilizer demand to 12.13 million tons, with a reduction potential of 53%. This study's evaluation of reasonable nitrogen fertilizer demand and exploration of green development pathways for nitrogen fertilizer will aid in implementing more scientific management systems and provide scientific support for the upgrading of China's nitrogen fertilizer industry.

    Reviews and Comments
    • Progress of Survey, Monitoring, and Control Technology of Benggang Erosion in Red Soil Hilly Area

      DENG Yusong, CAI Chongfa

      2025,62(2):322-333, DOI: 10.11766/trxb202312120526

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      Abstract:

      Benggang is aunique type of soil erosion in the south of China, which refers to the erosion phenomenon of collapse and scouring of the hillside damaged by the combined action of hydraulic force and gravity. Bengngang erosion is an advanced stage of gully development and is a permanent gully that cannot be filled in by farming practices. Benggang mainly occurs in the southern granite hill region which is mostly agricultural production, and its harmful effects are serious, destroying land resources, affecting agricultural production, and seriously impeding the coordinated and sustainable socio-economic development. Due to the complexity of the factors involved in the formation of Benggang, the knowledge of the mechanism and the management measures are still being explored. The objective of this study was to identify the current status of soil erosion in the region by outlining the survey methods of Benggang erosion, to obtain basic information on Benggang erosion, and to provide a scientific and theoretical basis for the development of soil and water conservation measures. Specifically, this study detailed the methodology, content, and purpose of individual Benggang surveys, and through this process grasped the basic characteristics of Benggang erosion. Subsequently, the methodology of investigating the regional influencing factors of the Benggang was introduced, which mainly includes the main influencing factors of the Benggang, such as geological geomorphology, climatic conditions, soil parent material, vegetation, and anthropogenic activities. Based on the investigation, this study also compiles the monitoring techniques of the Benggang used in recent years, combining the traditional manual methods with emerging technologies to truly and efficiently grasp the distribution characteristics, influencing factors and erosion development trend. Then, the research progress on the risk assessment and prediction methods of Benggang was reviewed to objectively assess the losses or impacts caused by Benggang disasters and to explore preventive and control measures. Finally, existing measures and models for the prevention and control of Benggang are discussed based on the survey of basic information on Benggang, field monitoring methods and risk assessment and prediction studies. Our investigation shed light on the current situation of erosion and the prediction of the development trend of Benggang, which is of great significance to the prevention and control of erosion in the Benggang region in China. The contents of the review in this study also assist in providing a basis for methods of investigation in the same erosion types, which can be generalized to the research of soil erosion in regions with similar geomorphology.

    • Research Progress on Soil Organic Phosphorus Mineralization and Its Regulation

      ZHANG Wannian, YANG Zi, YAN Yupeng, WANG Xiaoming, YIN Hui, XU Renkou, TAN Wenfeng, FENG Xionghan

      2025,62(2):334-347, DOI: 10.11766/trxb202404140154

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      Abstract:

      Soil organic phosphorus(P) is an important component of the soil P pool and its mineralization plays an important role in global P cycling. Understanding the mineralization of soil organic P is beneficial for the efficient utilization and management of P in terrestrial ecosystems. In recent years, the application of advanced techniques such as modern spectroscopy, chromatography, and mass spectrometry has provided crucial avenues for a more comprehensive characterization of the composition and structure of organic P. This review summarizes the applications of these technologies in quantifying changes in soil organic P content. Organic P, following mineralization, is converted into inorganic P(Pi), making it available for direct uptake and utilization by plants and microorganisms. Soil organic P mineralization is orchestrated by two primary pathways: enzymatic and mineral-mediated processes. Delving into the mechanisms of biological catalysis and abiological mineral-mediated catalysis is crucial for elucidating the control pathways of organic P. The mechanisms of soil organic P mineralization can be divided into biological mineralization driven by the oxidation of organic matter by microorganisms (phoA, phoD, and phoX) in response to energy demand, and biochemical mineralization driven by the release of Pi nutrients from plants in response to the demand for P nutrients mediated by phosphatases. Recent investigations have underscored the significance of minerals as an abiological mineralization pathway, shedding light on the mechanisms and actions of mineral-mediated catalysis. The surfaces of minerals (such as iron (hydro) oxides, manganese (hydro) oxides, and aluminum(hydro)oxides)provide an enzyme-like environment, facilitating the cleavage of phosphate ester (P-O-C) and terminal phosphoanhydride(P-O-P)bonds, resulting in the hydrolysis of organic P to Pi. In soil ecosystems, the biogenic elements carbon(C) and nitrogen(N) are intimately linked with soil organic P mineralization. From a nutrient factor perspective, elucidating the driving patterns of organic P mineralization can inform strategies to regulate soil P pools. Specifically, C effectively drives microbial mineralization of organic P, whereas N influences enzymatic metabolism, with the interplay between the two elements profoundly influencing the soil organic P mineralization process. The multiple forms of organic P present in soils are susceptible to influences from various external factors, which modulate phosphatase activity and alter organic P content, thereby further affecting the mineralization process. Various factors, including agricultural practices (such as fertilizer application, tillage practices, and biochar application), soil physical and chemical properties (such as pH, temperature, soil water content, and soil aeration status), microbial biomass, soil CO2 concentration, vegetation, and pollutants all impact soil organic P mineralization, resulting in corresponding environmental ecological effects. Therefore, regulating organic P mineralization is crucial for enhancing soil fertility and protecting the environment. Future strategies can focus on enhancing phosphatase activity, altering organic P composition, and increasing the abundance of phosphorus-solubilizing microorganisms to improve soil organic P mineralization. This review summarizes the advances in soil organic P mineralization research, synthesizing the soil processes, influencing factors, and control pathways, and highlighting the existing challenges and prospects.

    Research Articles
    • Research on Soil Type Inference Based on Combinatorial Cartography Method

      LI Kun, HUANG Wei, FU Peihong, CHEN Yuhao, WANG Ziying

      2025,62(2):348-361, DOI: 10.11766/trxb202402030056

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      Abstract:

      【Objective】 For the rational use of land resources, it is important to obtain accurate spatial distribution of soil types using digital soil mapping technologies. 【Method】 In this study, environmental factors were screened according to the soil parent material type based on field sampling points, and then three different mapping methods, random forest, SoLIM, and KNN, were used to map the zones according to the selected environmental factors, respectively. Each method was used individually to generate zoning maps, providing different reasoning for the spatial distribution of soil types. The zoning mapping results were obtained and combined to form a universal spatial distribution map of soil types, and then, we used the FP-Growth algorithm to effectively mine the internal correlation between environmental factors. By combining these associations with different mapping results obtained previously, the spatial distribution of soil types in the study area was deduced and used to obtain higher quality and precision inference results. 【Result】 The mapping results revealed several key findings: (1) The independent mapping of soil type based on the parent material type of soil by three different mapping methods is more effective and accurate than the joint mapping of all parent materials, and the inference of spatial distribution of soil types is also more reasonable. (2) Among the three mapping methods adopted in this study, the method combining random forest and frequent itemset mapping had the highest accuracy of 70.73%. Moreover, the results obtained by this combined method are similar to the spatial distribution of soil types inferred by the other two combined methods. Through comparative analysis, we were able to determine the approximate spatial distribution of soil species in the study area. (3) After the three mapping methods were combined with frequent itemsets, we observed that all methods had different degrees of improvement in accuracy verification and Kappa coefficient. Among them, the KNN method had the most significant improvement effect, the total mapping accuracy increased by 9.76%, and the Kappa coefficient increased by 11.70%. On the contrary, the random forest method had the smallest improvement, wherein, the total mapping accuracy and the Kappa coefficient increased by 4.88%, and 5.85%, respectively. These results validate the effectiveness of the combination method designed in this study. 【Conclusion】 The first, aspect of this study aimed to investigate the influence of soil parent material type on environmental factor screening. This aspect had relatively important reference significance for selecting appropriate environmental factors in the process of digital soil mapping. On the other hand, by combining frequent itemsets with the three different mapping methods used, this study not only provides a new method and idea for the exploration and application of digital soil mapping, but also provides a useful reference for the information application of frequent itemsets association.

    • Spatial Distribution of the Buried Depth and Thickness of Albic Soil Albic Layer in Sanjiang Plain and Its Influencing Factors

      DONG Fangjin, ZHANG Zhongbin, JIANG Fahui, WANG Jianhao, WANG Qiuju, Li Lujun, PENG Xinhua

      2025,62(2):362-374, DOI: 10.11766/trxb202311070459

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      Abstract:

      【Objective】 Albic soil is one of the main soil types with low productivity in Northeast China, mainly distributed in Sanjiang Plain. The soil profile is mainly composed of three layers, the black soil layer, the albic layer, and the illuvial layer. The albic layer has the physical characteristics of high bulk density, high strength, and poor aeration and water permeability, which is easily subjected to drought and waterlogging, thus, limiting crop root growth and yield formation. Its buried depth and thickness are closely related to the penetration depth and growth performance of crop roots, which are the key indexes to quantify the productivity of albic soil. However, little is known about the spatial distribution and driving factors of buried depth and thickness of the albic layer in the albic soil in Sanjiang Plain. The objective of this study was to investigate the spatial distribution pattern and driving factors of the buried depth and thickness of the albic layer in the albic soil in Sanjiang Plain. 【Method】 Based on classical statistics and geostatistics, the albic soil in the southeast of Sanjiang Plain ( Jidong County, Mishan City, Hulin City, and Baoqing County) was selected, and the soil profile of 0-60 cm was excavated. The thickness of the black soil layer and the albic layer was obtained by visual method, and the soils of the black soil layer, and the albic layer were taken for physical and chemical analysis. In addition, the meteorological, topographic, and parent material data of each sample point were collected. A total of 62 sampling points were obtained from 51 sampling points in the field and 11 points in the literature survey. 【Result】 (1) The average buried depth of the albic layer in the albic soil was 23.7 cm, and it gradually increased from southwest to northeast (13-37 cm). The average thickness was 18.5 cm, which gradually increased from southwest to northeast (8-35 cm), and the buried depth was opposite to the thickness of the albic layer in some local areas. (2) The burial depth of the albic layer was mainly affected by human tillage methods, and plough tillage increased the burial depth of the albic layer. (3) The thickness of the albic layer was negatively correlated with altitude ( r=–0.355, P<0.01), annual average evaporation ( r = –0.441, P<0.01), annual average temperature ( r=–0.273, P < 0.05), and clay mineral montmorillonite ( r=–0.432, P< 0.01), but positively correlated with annual average precipitation ( r=0.463, P<0.01), annual average humidity index ( r=0.461, P<0.01), coarse mineral hydromica (r=0.446, P<0.01), and coarse mineral quartz ( r=0.321, P<0.05). 【Conclusion】 The buried depth of the albic horizon in the Sanjiang Plain is related to tillage methods. The thickness of the albic horizon is mainly affected by meteorological topographic factors and soil minerals, resulting in a spatial distribution pattern of shallow and thin in the southwest and deep and thick in the northeast.

    • The Spatial Distribution of Particulate Organic Matter within Aggregates of Shajiang Black Soil Under Various Straw Return Practices Based on X-ray CT Technology and Machine Learning

      DING Tianyu, GUO Zichun, WANG Yuekai, JIANG Fahui, ZHANG Ping, PENG Xinhua

      2025,62(2):375-387, DOI: 10.11766/trxb202401310052

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      Abstract:

      【Objective】 Protection of particulate organic matter (POM)within soil aggregates has been recognized to be one of the principal mechanisms of C sequestration in soil. The low soil organic carbon (SOC) content of Shajiang black soil is a major factor for limiting crop yields in the Huaibei plain. Increasing SOC sequestration by returning crop residues to the field has been recommended. No-tillage (NT), rotary tillage (RT), and deep tillage (DT) with straw return (S) are commonly implemented. The objective of this study was to evaluate the spatial distribution of POM within aggregates in Shajiang black soil under various straw return practices. 【Method】 The six-year field experiment was conducted using X-ray CT technology and machine learning. The soil aggregates (6-8 mm in diameter) were collected from depths of 0-10, 10-20, and 20-40 cm. POM is divided into two parts: fresh residue and old POM, based on its morphological characteristics. 【Results】Overall, the POM within aggregates was primarily composed of fresh residues, comprising 76.4% to 87.0% across various soil layers under three different straw return practices. The distribution ratio of fresh residues in connected pores ranged from 0.266 to 0.788, while the distribution ratio of old POM varied between 0.177 and 0.569. There was a substantial quantity of POM was distributed within aggregates under NTS treatment in the 0-10 cm soil layer. Fresh residues and old POM were primarily distributed in the connected pores, with the proportions of 0.788 and 0.569, respectively. In the 20-40 cm soil layer, POM volume density within aggregates was highest under DPS treatment among all the treatments. Specifically, the proportions of fresh residue and aged POM distributed in the connected pores were 0.729 and 0.536, respectively. In comparison to the RTS treatment, the NTS led to a significant change in both the total POM volume density and fresh residue volume density by 54.4% and 56.7% within the 0-10 cm soil layer (P < 0.05), respectively. Additionally, the NTS treatment resulted in a 25.5% increase in the proportion of fresh residues in connected pores and a remarkable 96.4% increase in its volume density (P < 0.05). Furthermore, the DPS treatment resulted in a reduction of 37.4% in total POM and 40.4% in fresh residue volume density within the 0-10 cm soil layer (P < 0.05). However, there were no significant differences observed in the total POM volume density, porosity (>16 μm), or connected porosity of the aggregates among the NTS, RTS and DPS treatments within the 10-20 cm soil layer (P > 0.05). Compared with the RTS, the DPS treatment led to a significant increase in the total POM volume density by 2.78 times within the 20-40 cm soil layer, with the fresh residue and old POM volume density increasing by 3.10 and 1.72 times (P < 0.05), respectively. Additionally, the DPS treatment significantly increased the porosity of aggregates (>16 μm) and connected porosity by 74.2% and 142.8% within the 20-40 cm soil layer (P < 0.05), while it increased the fresh residue volume density and old POM volume density in the connected pores by 9.41 times and 7.96 times (P < 0.05), respectively. 【Conclusion】 The substantial increase in POM volume density within aggregates primarily stems from a significant rise in fresh residue volume density observed in the topsoil (0-10 cm)under no-tillage, as well as in the deeper soil (20-40 cm)following deep ploughing with straw incorporation. Connected pores serve as pivotal reservoirs for the storage and transformation of fresh residue through decomposition processes. Our findings suggest that deep tillage promotes the formation of connected pores and POM accumulation in the deeper soil layers, which is significant for improving agricultural soil quality and soil carbon sequestration in Shajiang black soil.

    • Evaluation of Improvement Effect and Analysis of Influencing Factors of Different Amendments on Saline-sodic Soils Based on A Meta-analysis

      HUANG Guangzhi, HUANG Lihua, LIU Baishun, JIANG Xiaotong, YANG Can, LIANG Yanping, CAI Jinghui

      2025,62(2):388-399, DOI: 10.11766/trxb202309060360

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      Abstract:

      【Objective】 Saline-sodic soils are widely distributed in the western part of the Songnen Plain. A variety of materials or measures have been used to improve soils in the process of long-term saline-sodic land management, and get great improvement effect. However, the improvement effect of these amendments on saline-sodic soils is mostly an assessment of individual factors, thus, the quantitative assessments for the impacts on multiple soil functions of different amendments are still lacking. 【Method】 Based on this, Our study used a meta-analysis to obtain 854 sets of relevant data from 589 papers on the improvement of saline-sodic soils in the past 30 years. The improvement effects of gypsum type amendment, biochar, and mixed amendments (combined application of 2 or more amendments)on saline-sodic soil and the factors influencing the improvement effect were quantitatively evaluated and analyzed with a meta-analysis and the Random Forest method. 【Result】 The results showed that the effects in saline sodic paddy fields of the three amendments on decreasing alkalinity were –29.1%, –38.6%, and –41.1%, respectively, and the effect of improvement was significant, however, the difference in improvement effectiveness between amendments was not significant. Furthermore, biochar (47.7%) had the best effects on improving soil nutrient content, while gypsum-type amendments (26.3%) were relatively the lowest. The three amendments were mostly used for soil amendment at the top soil layer (0～20 cm) of moderate and heavy saline-sodic soils, and there were differences in the application amount and application duration on the effect of soil improvement. Amendment application amount was a significant factor affecting the effectiveness in reducing soil salt/alkali of gypsum type amendments. 【Conclusion】 The main working principle of gypsum-type amendments is to reduce soil alkali, indirectly enhance soil nutrients and promote crop growth, whereas biochar and mixed amendments have the combined effect of reducing soil alkali and directly promoting soil nutrients. The selection of soil amendments should take into account not only the amount, but also the crop types, the cost of the amendments, the durability of the effect, and environmental safety issues.

    • Effect of Soil Acid Reduction and Fertilizer Cultivation Under Conditioner Application: Meta-analysis Based on Acid Soil Improvement Studies in China

      MING Runting, WAN Fang, NA Liping, WU Haicheng, WANG Wei, TAN Wenfeng, WU Yupeng

      2025,62(2):400-410, DOI: 10.11766/trxb202311050456

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      Abstract:

      【Objective】 This study aimed to accurately evaluate the effect of soil conditioner application on acid reduction and fertilizer cultivation of acidic soils in China. 【Method】 This study conducted a meta-analysis of 127 published literature, and identified the effects of acid soil conditioner application on soil acidity, soil fertility, and crop yield. 【Result】 The results showed that the acid reduction effect of the conditioner in extremely acidic soil (pH≤4.5) was the best. After application, the soil pH increased by 14.39%, and the reduction rates of exchangeable Al and exchangeable acidity reached 68.61% and 69.90%. The pH and basicity of the conditioner itself were the main factors affecting the acid-lowering effect of the conditioner, among which the lime conditioner had the best effect. It was observed that the soil pH increased by 18% and the exchangeable acidity decreased by 75.81% after application. The nutrient content of the conditioner itself and the amount of the conditioner were the main factors affecting the soil fertility after the conditioner application and the application of organic fertilizer had the best effect on the improvement of soil available nitrogen and available phosphorus (60.16%, 135.30% respectively). Also, biochar amendments had the best effect on the improvement of soil-available potassium and organic matter (75.52% and 76.02%). The application of amendments can reduce soil acidity and increase soil fertility to increase production, and biochar amendments had the best effects of increasing production, reaching 78.23%. 【Conclusion】 For managing acidic soils, it is recommended to apply high pH and high alkalinity amendments such as lime and biochar. For acidic soils with low organic matter content, it is recommended to apply high-alkalinity organic fertilizer, biochar and other amendments while biochar and mineral amendments are recommended for acidic soils with high organic matter content. For weakly acidic soil, it is recommended to apply common organic fertilizer. Nevertheless, it is necessary to further strengthen research on the combined application of inorganic and organic amendments to obtain a better effect on acid soil improvement.

    • The Influence of Ion Interface Reaction on the Permeability Pressure Characteristics of Typical Granite Benggang Sandy Loam Red Soil Layer in Anxi Country

      WU Yunbo, ZHANG Zhi, LI Xiaofei, MAO Xiaohua, ZHANG Yue, JIANG Fangshi, HUANG Yanhe, LIN Jinshi

      2025,62(2):411-421, DOI: 10.11766/trxb202401040012

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      Abstract:

      【Objective】 Rainfall can alter the movement of water in the soil of landslide-prone slopes, affecting the types and concentrations of ions in various soil layers, thereby influencing ion-interface reactions on soil particle surfaces. Additionally, moisture accumulation can exert high permeability pressure on the underlying soil layers, making them prone to deformation and instability. Soil with weaker resistance to permeability pressure, when closer to the surface, is more susceptible to soil erosion. Previous research has mainly focused on the influence of soil water stability and mechanical stability on landslide erosion, however, the impact of ion-interface reactions based on ion characteristics on the permeability characteristics of landslides is not well understood. 【Method】 This study focused on the red soil layer of a typical landslide in Anxi County and used ion solutions with different valences and concentrations to manipulate ion-interface reactions on the soil particle surfaces and analyzed their effects on the permeability characteristics of the landslide's red soil layer. 【Result】 K+ reduced soil porosity and decreased the soil's permeability and conductivity, while Mg2+ increased soil porosity and enhanced the soil's permeability and conductivity. There was a good single exponential increasing relationship between the permeability coefficient and the electrolyte concentration, with the fitting equations for various consolidation pressures expressed as k = ae–x/t+ b, R2> 0.845, P < 0.1. Also, K+ increased the electrostatic repulsion between soil particles, resulting in net repulsion forces between them, while Mg2+ reduced the electrostatic repulsion, leading to net attraction forces between soil particles. Higher electrolyte concentrations have a more significant impact on altering the internal forces within the soil. 【Conclusion】 Ion-interface reactions based on differences in ion characteristics can influence the internal forces of the soil, causing some degree of structural changes in landslide-prone soil.

    • Kinetic Study of Montmorillonite-humus Condensation Induced by Mixed Electrolyte

      HE Aizhou, YU Linqiao, LI Hang

      2025,62(2):422-435, DOI: 10.11766/trxb202311080466

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      Abstract:

      【Objective】 Natural soil typically consists of a variety of colloids and multiple electrolytes coexisting simultaneously. However, existing studies on soil colloid coagulation have mostly been conducted under conditions involving a single electrolyte and a single colloid. In this study, the coagulation dynamics of a mixed colloid system comprising montmorillonite and humic acid under mixed electrolyte conditions were systematically investigated attempting to explain the coagulation effect and mechanism of mixed electrolyte on the mineral-organic mixture. 【Method】 Using dynamic laser scattering (DLS) technique, the coagulation kinetics of montmorillonite colloids and montmorillonite-humic acid mixed colloids under the influence of mixed electrolytes were studied by considering key parameters such as the average coagulation rate, critical coagulation concentration (CCC), and coagulation activation energy. 【Result】 The results revealed the following key findings: (1) Under mixed electrolyte conditions, whether involving a single colloid or a mixed colloids, there was only one CCC. This indicates that under mixed electrolyte conditions, both the two cations in the mixed electrolyte system play a cooperative role in the coagulation of the colloid. Although both cations collaboratively influenced colloid coagulation, the analysis of colloid coagulation rate, CCC, and coagulation activation energy revealed that the cation with stronger competitive adsorption ability played a decisive role. For example, in the 99% Mont (Montmorillonite) + 1% HA(Humic acid)mixed colloids system, the CCC (97.41 mmol·L–1) of the Na+ + K+ mixed system closely resembled the CCC (94.91 mmol·L–1) of K+ alone system, indicating that the role of Na+ in the coagulation of this mixed colloid was almost negligible. This implies that in the Na+ + K+ mixed system, K+ plays a decisive role in colloid coagulation. (2) Increasing the content of humic acid significantly enhanced the stability of the mixed colloid, resulting in the requirement of a higher electrolyte concentration to induce colloid coagulation. This effect can be attributed to the fact that the addition of humic acid increased the surface charge density of the organic/inorganic composite colloidal particles, thereby strengthening the electrostatic repulsion between particles. 【Conclusion】 The scientific findings of this study not only provide guiding significance for further unraveling the formation mechanism of soil organic-inorganic complexes, but also shed light on the cooperative role of cations in colloidal coagulation under mixed electrolyte conditions. The results underscore the decisive role of the cation with stronger competitive adsorption ability in colloid coagulation. Furthermore, the study reveals that increasing the content of humic acid significantly enhanced the stability of the mixed colloid, necessitating a higher electrolyte concentration to induce colloid coagulation. These insights contribute to the understanding of the complex interplay between organic and inorganic components in soil, paving the way for future research in this field.

    • Effect and Mechanism of Polystyrene on the Co-transport of Copper and Soil Colloids in Saturated Porous Media

      GONG Jiaqi, DONG Yanan, XU Shaohui, LIN Qing

      2025,62(2):436-447, DOI: 10.11766/trxb202401150028

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      Abstract:

      【Objective】 The ubiquitous colloidal substances in the environment profoundly affect the transport and transformation of pollutants in soil and groundwater. The impact of microplastics, as an emerging pollutant, on the transport of colloids and colloid-associated pollutants is still unclear. 【Method】 Therefore, column experiments were conducted in saturated quartz sand, with polystyrene (PS) microplastics as the research object. By combining with sedimentation experiments, Fourier infrared spectroscopy (FTIR), and other methods, the influencing mechanisms of microplastics on soil colloid, copper (Cu2+), and their co-transport were investigated. 【Result】 The results showed that PS facilitated the transport of soil colloids through mechanisms involving heterogeneous aggregation with soil colloids, competition for surface sites on quartz sand, and steric hindrance. This promotional effect was more pronounced in the presence of Cu2+. In comparison to soil colloid, the effect of PS on Cu2+ migration was not obvious due to its low concentration as well as low adsorption capacity. In the presence of PS, 83.47% of Cu2+ was transported in dissolved form, while 35.25% of Cu2+ was transported in colloidal form under the effluence of soil colloid. PS enhanced the mobility of soil colloids, but it concurrently reduced the adsorption of Cu2+ and facilitated the transport of dissolved Cu2+ compared to the scenario with only soil colloids. However, PS did not have a significant impact on the effluent concentration of total Cu. Furthermore, the mobility of PS was also influenced by soil colloids and Cu2+. 【Conclusion】 In general, microplastics in the soil environment not only directly interact with Cu2+, but also alter the properties of soil colloids. Changes in colloidal properties may be the primary reason for the impact of microplastics on the environmental behavior of Cu.

    • Environmental Footprint Assessment of in Situ Chemical Oxidation Remediation for Contaminated Aquifer Based on SiteWiseTM Method

      LIU Peng, SANG Chunhui, ZHANG Hongzhen, XIAO Meng, MENG Hao, LI Xianglan

      2025,62(2):448-458, DOI: 10.11766/trxb202312090523

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      Abstract:

      【Objective】 The environmental footprint assessment of in-situ chemical oxidation remediation technology (ISCO) for polluted sites has important scientific research value and practical significance for promoting green and sustainable remediation. However, its application in chlorinated hydrocarbon-contaminated sites has not received much attention. 【Method】 This study employed the ISCO method to remediate a chlorinated hydrocarbon-contaminated site. The remediation of polluted sites using ISCO is divided into four stages: material consumption, transportation process, remediation process, and sampling testing. SiteWiseTM tool was used to conduct an environmental footprint assessment. 【Result】 The results showed that using ISCO technology to remediate 73 800 cubic meters of polluted aquifers resulted in 1 261 tons of greenhouse gas (GHG) emissions, total energy consumption of 16 876 GJ, 4 096 kg of SOx emissions, 2 678 kg of NOx emissions, and 912 kg of particulate matter 10(PM10) emissions. The environmental footprint mainly came from the use of materials such as sodium persulfate and sodium hydroxide, and the consumption of construction electricity caused higher atmospheric pollutant emissions. The Monte Carlo analysis results indicated that the coefficient of variation of greenhouse gas emissions was less than 10%. Also, the sources of uncertainty in this study mainly included redundant designs from ISCO, as well as significant differences in mechanical efficiency and emission factors between different countries. 【Conclusion】 The SiteWiseTM tool has reference value for the environmental footprint assessment of ISCO remediation projects in polluted sites in China and future researchers should update it locally by considering machinery types and efficiencies, emission factors, and units of measurement. These considerations will improve applicability to the environmental footprint assessment of polluted sites in China.

    • Characteristics of Natural Humus Modified Materials and Their Growth- promoting Effects on Maize Under Drip Irrigation

      CHEN Zhuo, ZHANG Congzhi, ZHANG Jiabao, ZHAO Bingzi, PAN Hui

      2025,62(2):459-471, DOI: 10.11766/trxb202312170531

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      Abstract:

      【Objective】 This study aims to analyze the physicochemical properties of two natural humus-modified materials (M1 and M2) produced by different processing methods, compare the differences between the two materials, and investigate their effects at different concentrations on the growth of maize under drip irrigation conditions. The goal is to explore the most suitable application concentration and amount of humus under drip irrigation and provide new perspectives and practical bases for agricultural production. 【Method】 The content of humus and its components in M1 (natural humus sand grinding fluid) and M2 (fully water-soluble potassium nitrohumate) was determined and the physical and chemical properties of the materials were analyzed through elemental analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR). Then, field experiments were designed to evaluate the effects of applying different concentrations (0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0 g·L–1) and amounts (650, 1 300, 1 950 L·hm–2) of M1 and M2 on the height, biomass, and yield of maize. 【Result】 The results showed that: 1) There were significant differences in chemical composition between M1 and M2. M1 had a higher content of humus, larger molecular weight, more complex structure, and stronger stability in soil. On the other hand, M2 had a lower total content of humus, a high content of fulvic acid (FA), a smaller molecular weight, and a lower degree of humification. 2) The microstructure of M1 and M2 differed. M1 had a rough and complex particle surface with uneven particle size while M2 exhibited a smoother and looser sponge-like appearance with no chaotic structure on the particle surface. FTIR analysis showed that M1 may contain more aromatic structures or carboxylate salts and silicate impurities while M2 may contain more carboxyl groups. 3) Although the application of M1 and M2 had little effect on plant height, it significantly increased the biomass and yield of maize. Especially for M2, when its concentration was 1.0 g·L–1 and the amount was 1 300 or 1 950 L·hm–2, the biomass of maize plants increased significantly by 40.11% and 40.74% and the yield increased significantly by 25.75% and 27.45%, respectively. 【Conclusion】 The application of different concentrations and amounts of M1 and M2 effectively promoted the growth of maize, with M2 exhibiting greater growth potential under the same conditions. This may be attributed to the role of humus in improving soil structure, increasing and retaining soil moisture and nutrient content, activating specific biochemical pathways, and enhancing soil microbial activity, thereby improving the nutrient absorption efficiency and photosynthetic capacity of maize plants. Considering factors such as cost, it is recommended to apply M2 at a concentration of 1.0 g·L–1 and an amount of 1 300 L·hm–2 in the field to fully exploit its effects in promoting maize growth potential and increasing yield. This provides new perspectives and practical bases for the efficient utilization of humus in agriculture.

    • Effect of Basal Application of Magnesium Sulfate and Magnesium Chloride on Seed Yield and Quality of Rapeseed

      GENG Guotao, YE Xiaolei, YU Xiaohong, REN Tao, CONG Rihuan, LI Xiaokun, ZHANG Yangyang, LU Zhifeng, LU Jianwei

      2025,62(2):472-483, DOI: 10.11766/trxb202311180483

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      Abstract:

      【Objective】 Rapeseed (Brassica napus L.), one of the most important oilseed crops in China, is sensitive to magnesium (Mg) deficiency. The Yangtze River Basin is the main planting area for winter oilseed rape in China, and the climatic characteristics of the region with simultaneous rain and heat, high-intensity planting patterns and long-term unbalanced fertilization have led to serious depletion of soil magnesium. It provides a theoretical basis for the rational application of Mg fertilizers in rapeseed cultivation to investigate the impact of different Mg fertilizers on seed yield and quality of rapeseed in China’s main winter oilseed rape production areas. 【Method】 Between 2019 and 2020, 56 field trials were conducted in the main rapeseed-growing regions in China. The trials followed a one-way experimental design, with three distinct Mg fertilizer treatments: no Mg fertilizer (CK), magnesium sulfate at the rate of 45 kg·hm–2(Calculated as MgO, the same as below) (MgSO4·H2O, referred to as MgSO4), and magnesium chloride, also at the rate of 45 kg·hm–2 (MgCl2,referred to as MgCl2). The response of rapeseed to the two Mg fertilizers was evaluated by analyzing the rapeseed yield, yield components, oil, protein, sulfide content and fatty acid fractions. 【Result】 The results revealed that the application of both MgSO4 and MgCl2 significantly increased rapeseed yield by 14.1% and 11.8%, respectively. The increase was primarily attributed to an increase in pod number per plant and seeds per pod. MgSO4 and MgCl2 increased the pod number per plant by 10.2% and 8.2%, and the seeds per pod by 3.9% and 2.4%, respectively. Analyzing the relationship between soil Mg content, sulfur content and yield increase resulting from Mg application indicated that the increase in seed yield was mainly associated with soil Mg content but not soil sulfur. The addition of MgSO4 and MgCl2 resulted in an 11.8% and 8.7% increase in seed Mg content (relative to no Mg application treatment), respectively. However, Mg accumulation was similar in both Mg application treatments. Additionally, the application of Mg fertilizer significantly improved rapeseed quality by increasing oil, oleic acid, and linoleic acid content by 5.5% and 4.8%, 8.3% and 7.7%, 7.8% and 11.4% for MgSO4 and MgCl2, respectively. Meanwhile, stearic acid, palmitic acid, and erucic acid contents were decreased by 4.60% and 26.1%, 7.5% and 13.9%, and 33.2% and 24.1% for MgSO4 and MgCl2, respectively. Although the application of MgSO4 resulted in a significant increase in sulfide, it remained below the national limits for edible rape oil and feed cake meal for double-low oilseed rape. 【Conclusion】 In the main winter oilseed rape production areas in China, the application of MgSO4 and MgCl2 can significantly increase rapeseed yield, with MgSO4 having a slightly greater effect compared to MgCl2. Magnesium application also increases the Mg content and improves the oil quality of rapeseed by increasing the content of oleic acid and linoleic acid while reducing stearic acid and palmitic acid contents. These synergistic improvements contribute to both yield and quality enhancement.

    • Effects of High CO2 Concentration on Soil Organic Carbon Mineralization

      WANG Ruoyao, LI Yuanyuan, XIA Bin, GAO Zihui, ZHAO Yunge, XU Mingxiang

      2025,62(2):484-494, DOI: 10.11766/trxb202312010505

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      Abstract:

      【Objective】 Soil CO2 concentration is often higher than that of the atmosphere. Current studies on soil organic carbon mineralization are mostly conducted under conditions of increasing atmospheric or simulated atmospheric CO2 concentration. This may lead to deviation of the results from the actual organic carbon mineralization process in the soil profile or impose some bias on indoor mineralization incubation experiments towards the “mineralization potential” rather than the actual mineralization rate. How and to what extent soil organic carbon mineralization is affected by high CO2 concentrations in the soil profile? The lack of a clear answer to this question limits the comprehensive understanding of soil organic carbon stability. 【Method】 In this paper, an indoor mineralization incubation test was conducted with six CO2concentration gradients of CK (400 µmol·mol–1, atmospheric level), 800, 2 000, 4 000, 6 000, and 8 000 µmol·mol–1, and three replicates were set for each treatment. The effects of different concentrations of CO2 on the rate of soil organic carbon mineralization, cumulative mineralization, and active organic carbon fractions were investigated, and the extent to which CO2 concentration and other influencing factors explained the cumulative mineralization was analyzed. 【Result】 The results showed that: 1) High concentration of CO2(2 000-8 000 µmol·mol–1) in soil significantly inhibited the mineralization of soil organic carbon, with the mineralization rate decreasing by 6.27%-45.61%, and the cumulative amount of mineralization decreased by 1.72%-40.82%; 2) Lower concentration of CO2(800 µmol·mol–1) in soil significantly promoted the mineralization of soil organic carbon, the mineralization rate increased by 4.38%-12.65%, and the cumulative mineralized amount increased by 17.37%-48.43%; 3) The CO2 concentration in the soil effected the content of active organic carbon fractions. At a range of CO2 concentrations, soil microbial biomass carbon (MBC) content increased significantly and dissolved organic carbon (DOC) content decreased significantly compared to CK. However, the content of easily oxidizable organic carbon (EOC) was not significantly changed; 4) The mineralization characteristics of organic carbon showed a significant negative correlation with CO2 concentration, a significant positive correlation with DOC, a negative correlation with EOC, and no significant correlation with MBC; 5) Under the appropriate conditions of temperature and humidity, the contribution of CO2 concentration to the cumulative mineralization of soil organic carbon reached 22.93%. 【Conclusion】 High CO2 concentration significantly inhibited soil organic carbon mineralization by affecting the soil organic carbon readily available carbon source, which may be one of the important factors to maintain soil organic carbon stability.

    • Characteristics of Soil Organic Carbon Fraction Accumulation and Stability Under Different Rice-rape Rotation Measures

      SHU Yeqin, PENG Fuxi, LEI Wenshuo, JIANG Tongtong, CHEN Yumei, LIU Weimin, ZHANG Zhenhua, XIA Yinhang

      2025,62(2):495-503, DOI: 10.11766/trxb202311030452

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      Abstract:

      【Objective】 Rape multiple-cropping is an important planting mode to promote grain stabilization and rapeseed increase in South China rice growing area. We explored the influence of soil organic carbon (SOC) accumulation and its stability characteristics under different rice–rape rotation measures with whole-straw returning, which is of great significance for in-depth analysis of soil carbon cycle in paddy fields by making full use of winter fallow fields to plant rape. 【Method】 This study is based on an 8-year yield localization experiment. In contrast with rice–rice–winter fallow, we explored the characteristics of SOC and its fraction accumulation under three rice–rape rotation treatments: rice–rice–rape, rice–rape tillage, and rice–rape no tillage. 【Result】 The results indicated that the content of SOC in 0–20 cm soil layer was increased by 5.28%–25.12% under the three rice–rape rotation treatments, especially under the rice–rice–rape treatment. Also, the increasing rate of SOC in 20–40 cm soil layer was 18.48%—43.97%, among which the rice–rape tillage and the rice–rape no tillage treatment reached a significant level.The content of mineral-associated organic carbon (MAOC) from all the rice–rape rotation measures was increased significantly in different soil layers. At the same time, the ratio of particulate organic carbon (POC) to SOC was significantly decreased while the ratio of MAOC to SOC increased in each treatment from both 0–20 cm and 20–40 cm soil layer. The increasing rate of MAOC/SOC were 2.31%–7.49% and 1.56 %–2.66% in the two soil layers, respectively. Possible causes of these results may be that rice–rape rotation increased the activity of organic carbon invertase enzyme (β-glucosidase、β-1, 4-glucanase and Laccase) as well as microbial biomass carbon in 0–20 cm soil layer to varying degrees, thereby promoting the conversion of POC to MAOC. 【Conclusion】 In summary, rape multiple-cropping in winter fallow not only promoted the accumulation of SOC in paddy field, but also increased the ratio of MAOC/SOC, ultimately enhancing the stability of soil carbon pool.

    • Effects of Iron Oxides on the Priming Effect of Topsoil and Subsoil Carbon Decomposition in a Subtropical Forest

      ZHANG Yuting, XU Wenhao, WANG Qingkui, TIAN Peng

      2025,62(2):504-516, DOI: 10.11766/trxb202401030009

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      Abstract:

      【Objective】 The relationship between soil organic carbon and iron oxides is crucial to the regulation of soil carbon stability. In terrestrial ecosystems, subsoil is an important organic carbon reservoir, which has been paid increasing attention due to its dynamic processes. However, little is known about how carbon inputs affect the interactions between soil minerals and organic carbon, especially in the subsoil. 【Method】 To address the knowledge gap, this study investigated the effects of two different crystalline forms of iron oxides, goethite and ferrihydrite, on the priming effect of topsoil (0~10 cm) and subsoil (20~40 cm) in subtropical forests. We incubated the soils by adding 13C-labeled glucose to quantify the intensity of the priming effects in a laboratory experiment. 【Result】 The results show that the priming effects of topsoil and subsoil were 1.63 mg·g–1and 0.61 mg·g–1, respectively, indicating that the priming effects decreased with soil depth. An interactive effect was observed between the type of iron oxides and soil depth on the priming effect of SOC. In topsoil, the addition of goethite significantly decreased the intensity of the priming effect (P < 0.05), while ferrihydrite showed no significant influence on it. In the subsoil, the addition of ferrihydrite significantly increased the intensity of the priming effect (P < 0.05), but the addition of goethite had no significant effect on the priming. In topsoil, after goethite was added, the co-precipitation produced iron-bound organic carbon, which inhibited the mineralization of organic carbon, influenced microbial carbon limitation, and further decreased the intensity of the priming effect. In the subsoil, the intensity of the priming effect was influenced by the limitation of microbial carbon and phosphorus. Glucose acted as an electron shuttle, increasing iron reduction and CO2 production. The reduction and dissolution of ferrihydrite reduced the protective effect of iron oxide on SOC, which in turn enhanced the mineralization of SOC. Iron oxides can increase SOC accumulation and stability through mineral protection and lead to SOC mineralization through redox reaction. 【Conclusion】 Overall, the priming effects of topsoil and subsoil have different responses to iron oxides, and the influence of iron oxides on organic carbon accumulation is affected by their properties and soil conditions.

    • Short-term Low Nitrogen Addition Alters the Molecular Composition and Stability of Soil Dissolved Organic Matter in a Pinus taiwanensis Forest

      YUAN Xiaochun, ZHANG Xiaoqing, ZHOU Qian, WU Lianzuan, CHEN Junming, ZENG Quanxin, BAI Xinyu, LI Wenzhou, CHEN Yuemin

      2025,62(2):517-527, DOI: 10.11766/trxb202311160476

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      Abstract:

      【Objective】 Dissolved organic matter (DOM) is highly sensitive to environmental changes, and its dynamic changes are crucial for understanding regional/global carbon cycling under global change scenarios. However, it is not yet clear how the characteristics of soil DOM molecules change under nitrogen deposition. This study aimed to investigate the response of DOM molecular composition and stability to nitrogen addition. 【Method】 In this study, three nitrogen addition levels (0, 40, and 80 kg·hm–2·a–1) were conducted in a Pinus taiwanensis forest by using urea addition to simulate nitrogen deposition in the field. The effect of short-term (three years) nitrogen addition on the molecular composition of DOM and its stability was investigated using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). 【Result】 The results of FT-ICR MS analysis revealed that DOM molecules were mainly concentrated in 250-400 Da, and CHO compounds accounted for more than 50% of all compounds. Of the eight types of DOM molecules, lignin-like molecules dominated all soil DOM molecules, followed by tannins and condensed aromatics, with the relative abundance of readily decomposable small molecules (including lipids, proteins, and carbohydrates) being low. There was no statistically significant change in the content and optical properties of DOM under nitrogen addition, but significant changes occurred in the properties and composition of DOM molecules. Compared to high nitrogen treatment, low nitrogen treatment significantly reduced the relative abundance of carbohydrate molecules in DOM by 73.33%. This may be largely attributed to the increase in microbial biomass and hydrolytic enzyme activities. Nitrogen addition did not change the nitrogen-containing compounds in DOM molecules, but reduced the sulfur-containing compounds. Furthermore, the average molecular weight and ratio of double bond equivalent to carbon atom number (DBE/C), modified aromaticity index (AImod), and aromaticity equivalent (Xc) of DOM molecule did not show significant changes under nitrogen addition. However, a significant increase in DBE values was observed under low nitrogen addition, indicating an improvement in the molecular stability of DOM. The improvement of DOM molecular stability may have a potential impact on soil carbon pool stability. Pearson's correlation analysis revealed that DBE values were significantly negatively correlated with small molecule compounds such as carbohydrates and proteins/amino sugars, while the correlation with large molecules such as lignin and condensed aromatics was not significant. Besides, nitrogen addition did not significantly change the difficult-to-decompose molecules such as lignin and condensed aromatic compounds in DOM. This suggests that the molecular stability of DOM under short-term nitrogen addition may depend on the removal of readily decomposable small molecules, such as carbohydrates, rather than the increment of refractory molecules. 【Conclusion】 Collectively, this study provides a new perspective at the molecular level for understanding the behavior of soil DOM under nitrogen deposition, and a reference for understanding the potential relationship between DOM molecules and soil carbon stability.

    • The Microbial Diversity of Reclaimed Soil Drives Its Multifunctional Variation in the Eastern Plain Mining Area

      MA Jing, HUA Ziyi, YOU Yunnan, ZHU Yanfeng, ZHNAG Qi, CHEN Fu

      2025,62(2):528-542, DOI: 10.11766/trxb202401010001

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      Abstract:

      【Objective】 Land reclamation is a significantly important way to restore soil productivity in high groundwater mining areas. However, most of the reclaimed soil always shows poor functions, such as lower fertility and biodiversity, while the in-depth understanding of microbiological mechanisms underlying the formation and restoration of multifunctional reclaimed soil is still deficient. 【Method】 Four reclamation plots including 9 years, 12 years, 15 years, and 18 years of reclamation, and 1 control plot from the Dongtan mining area in Zoucheng City, Shandong Province, were selected as the research objects. A total of 75 surface soil samples were collected, and 18 soil physical, chemical, and biological indicators such as organic carbon were measured to explore the interaction between soil microbial communities and soil multifunctionality, as well as the microbiological mechanisms of multifunctionality variation. Moreover, based on the molecular ecological network methods, supplemented by statistical analysis methods, several microbial networks were constructed to investigate the interaction between microbial community diversity, network structure, and soil multifunctionality. 【Result】 The results showed that: (1) Land reclamation activities and the normal vegetation rotation of the cultivated land have significantly improved soil multifunctionality, with soil multifunctionality almost reaching the undisturbed control level after 18 years of reclamation. Moreover, among the soil properties, soil organic carbon, pH, available phosphorous, and most enzyme activities were important influencing factors for multifunctionality. (2) With the increasing reclamation years, soil microbial diversity significantly increased, while the richness performance of bacteria and fungi was different. The increasing trend of bacteria was not significant after 12 years of reclamation whereas fungi increased significantly until 18 years of reclamation. However, the abundance of bacteria and fungi reached normal farmland levels after 15 years and 18 years of reclamation, respectively. (3) The analysis results of the microbial co-occurrence network showed that the nodes, edges, average degree, average path length, network density, clustering coefficient, and betweenness centrality in the bacterial community co-occurrence network significantly increased with the increase of reclamation time. Moreover, the topological properties of bacterial and fungal subnetworks such as edge, degree, and network density were significantly positively correlated with soil multifunctional properties. The diversity of microbial communities showed a positive impact on the network complexity, enhancing the association between species and thereby enhancing their versatility. Both the complexities of bacterial and fungal community networks presented significant correlations with soil multifunctionality. The impact of bacterial network complexity on soil multifunctionality was not affected by other indicators, whereas the correlation between fungal network complexity and soil multifunctionality was influenced by bacterial richness, soil microbial diversity, and fungal richness. The structural equation model results indicated that microbial diversity can directly and positively regulate soil multifunctionality, or indirectly manipulate soil multifunctionality by positively influencing the network complexity of bacteria and fungi. 【Conclusion】 This study has revealed the driving mechanism of multifunctional restoration of reclaimed soil in the eastern plain mining area, which would provide important guidance for the deeper understanding of the development and functional succession of reclaimed soil microbiota, as well as soil quality management and protection.

    • Effects of Long-term Nitrogen Application on the Soil Ammonifier and Nitrogen Mineralization

      LIU Lingzhi, GUO Bingqing, WANG Feng, MENG Ao, LIANG Minjie, AN Tingting, WANG Jingkuan

      2025,62(2):543-554, DOI: 10.11766/trxb202310310445

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      【Objective】 Ammoniation is the process by which microorganisms convert organic nitrogen into inorganic nitrogen, which can improve soil nitrogen supply. Under different long-term fertilizer application scenarios, soil organic nitrogen undergoes significant changes, which makes comprehension of its ammonification process challenging. 【Method】 This study relied on a 29-year long-term targeted fertilization experiment at Shenyang Agricultural University, targeting four different fertilization treatments, including no fertilization (CK), chemical fertilizer (HCF), chemical fertilizer reduction (LCF), and fertilizer reduction combined with organic fertilizer (CMF), considering three soil depths (0-20 cm, 20-40 cm, and 40-60 cm), and three sampling period (pre-planting, maize tasseling stage and post-harvest). Using the real-time fluorescence quantitative PCR (qPCR) method, the abundance, activity, and nitrogen mineralization changes of soil ammonification gene gdh in different soil layers were studied during maize growth period after long-term different fertilization treatments. Also, the effects of fertilization, season, soil depth, and their interactions on ammonifier and soil net nitrogen mineralization rate were evaluated. 【Result】 The results showed that: 1) Compared with soil layer and fertilization treatment, the sampling period had the most significant impact on the abundance and activity of gdh genes. During the three sampling periods, the soil gdh gene activity and net nitrogen mineralization rate during the maize tasseling stage were significantly higher than pre-planting and post-harvest (P < 0.05) ; 2) Compared with no fertilization (CK), long-term application of chemical fertilizers (LCF and HCF) significantly increased soil nitrogen mineralization rate during the tasseling period (P < 0.05) while reduction of fertilizer combined with organic fertilizer (CMF) showed stable or increased soil nitrogen mineralization rate in post-harvest; 3) The abundance and activity of ammonifiers were significantly positively correlated with soil net nitrogen mineralization rate, and the ammonium nitrate ratio was an important factor affecting ammonifiers (P < 0.01). 【Conclusion】 In summary, nitrogen application, and crop absorption change the soil ammonium nitrate ratio, causing differences in the abundance and activity of soil ammonifiers. This led to changes in soil nitrogen mineralization rate. Long-term application of LCF and HCF is beneficial for increasing the rate of surface soil nitrogen mineralization in pre-planting and tasseling. CMF can help stabilize the activity of soil ammonifiers in post-harvest and promote the ammonification process of soil organic nitrogen.

    • Screening of Indigenous Microbial Helpers for the Chlorpyrifos-degrading Bacterium Shingopyxis granuli CP-2

      LI Mei, WANG Zhongyang, JING Lili, HOU Yugang, MA Liya, SHENG Hongjie, YU Xiangyang

      2025,62(2):555-564, DOI: 10.11766/trxb202311200486

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      Abstract:

      【Objective】 Chlorpyrifos residue poses a significant challenge to food safety. Microbial degradation which is called bioaugmentation is an effective approach for the elimination of such residues. Bioaugmentation often involves an invasion process requiring the establishment and activity of a foreign microbe in the resident community of the target environment. Interactions with resident micro-organisms, either antagonistic or cooperative, are believed to impact invasion. However, few studies have examined how the interactions between the invaded degrading bacteria and resident microorganisms in the target environment can influence microbial degradation. In this study, chlorpyrifos-degrading bacteria Shingopyxis granuli CP-2 was used as material, from the perspective of microbe-microbe interactions, to select resident bacterial helper of CP-2. 【Method】 Soils from the field were first collected, a batch of bacteria from the soil was isolated by continuous dilution method, and identified by full-length sequencing of the 16S rRNA gene. The 16S rRNA gene sequences of all isolates were aligned using MUSCLE. Sequences in the alignment were trimmed at both ends to obtain maximum overlap using the MEGA X software, which was also used to construct taxonomic cladograms. A maximum-likelihood (ML) tree was constructed, using a general time reversible (GTR) + G + I model, which yielded the best fit to our data set. Bootstrapping was carried out with 100 replicates retaining gaps. A taxonomic cladogram was created using the EVOLVIEW web tool (https: //evolgenius.info//evolview-v2/). The taxonomic status (phylum) of each rhizobacterial strain was also added as heatmap rings to the outer circle of the tree. The resident bacterial helper which could promote the growth of CP-2 was then screened by supernatant assay from the isolates isolated from soils, and the bioinformatics results of these helpers were analyzed. At last, a bacterial isolate which well promoted the growth of CP-2 was chosen, and its effect on CP-2's ability to degrade chlorpyrifos was investigated in vitro. 【Result】 109 strains of indigenous bacteria were isolated and were classified into four main phyla: Proteobacteria (54.1%), Actinobacteria (14.8%), Firmicutes (15.6%), and Bacteroidetes (15.6%). Among them, 41.3% significantly inhibited the growth of CP-2, 17.4% had no significant effect on CP-2, and 41.3% (45 bacterial strains) significantly enhanced CP-2's growth and were identified as indigenous bacterial helpers of CP-2. The 45 bacterial strains in the helper bank mainly belong to 3 phyla, 4 classes, 7 orders, 13 families and 20 genera. One strain (B72), which exhibited a strong growth-promoting effect on CP-2 was selected to assess its impact on chlorpyrifos degradation by CP-2. The results demonstrated that both the bacterial strain B72 and its supernatant significantly promoted the chlorpyrifos degrading ability of CP-2. 【Conclusion】 Together, the strains identified in this study provide valuable resources for future research and applications involving microbial degradation of soil toxicants such as chlorpyrifos or other pollutants. Furthermore, the indigenous bacterial helper of chlorpyrifos degrading bacterium CP-2 significantly promoted its ability to degrade chlorpyrifos, which offers theoretical guidance and technical support for potential co-inoculation strategies involving both chlorpyrifos-degrading bacteria and indigenous bacterial helpers aimed at pollution remediation.

    • Effects of Facility Cultivation Pattern on Soil Bacterial Community in Ningxia Region

      SUN Yinqinqin, YAN Yuanyuan, QU Jisong, ZHANG Lijuan, ZHU Qiannan, ZHAO Jun, ZHANG Jinbo, CAI Zucong, HUANG Xinqi

      2025,62(2):565-578, DOI: 10.11766/trxb202312070519

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      【Objective】 Soil bacterial community characteristics are important indicators of soil quality, however, little is known about the effects of facility cultivation on soil microbiological properties. Thus, clarifying the responses of soil bacterial community and functions to facility cultivation is of significance for the sustainable utilization of facility soil. 【Method】 To reveal the change of soil bacterial community under intensive cultivation and its main influencing factors, this study collected and analyzed 67 facility-open field paired soil samples in Ningxia region. Based on amplicon sequencing technology, the effects of facility cultivation on soil bacterial community diversity, composition, interspecific interaction, and assembly process were investigated. 【Result】 The results showed that compared with the open field soil, the number of bacteria, Shannon, ACE, and Pielou indices of the bacterial community increased by 63.3%, 3.20%, 11.4%, and 1.69%, respectively. The facility cultivation significantly changed the soil bacterial community structure. Redundancy analysis (RDA) showed that the content of available phosphorus, pH, and electrical conductivity were the main environmental factors determining bacterial community structure. Physicochemical parameters such as pH and soil available nutrient contents significantly affected the bacterial community composition of the facility soil, and the climatic factors including annual average precipitation and annual average temperature significantly affected the bacterial community composition of the open field soil. At the phylum level, the relative abundances of Planctomycetota and Firmicutes increased significantly, while the relative abundances of Gemmatimonadota and Myxococcota decreased significantly in the facility soil. At the genus level, the dominant genera such as Bacillus and Pseudomonas were enriched in the facility soil. Co-occurrence network analysis showed that the edge, average degree, clustering coefficient, and modularization degree of the bacterial network in the open field soil increased by 10.8 times, 11.0 times, 36.8%, and 1.78 times compared to those in the facility soil, respectively. Also, facility cultivation significantly reduced the complexity and modularization degree of the soil bacterial network. Functional prediction using the Functional Annotation of Prokaryotic Taxa (FAPROTAX) database showed that facility cultivation significantly increased the relative abundance of carbon, nitrogen, and other element cycles and bacterial functional groups related to pathogenic bacteria. The distance decay relationship of the bacterial community in the facility soil was weaker than that in the open field soil. The community assembly was greatly affected by the deterministic process and the diffusion limitation was higher in the facility soil compared to that in the open field soil. 【Conclusion】 Collectively, facility cultivation in Ningxia region significantly changed multiple properties of the soil bacterial community. These results can provide theoretical guidance for the sustainable utilization of local facility soil.

    • Isolation, Identification, and Characteristics of Autotrophic Nitrogen-fixing Bacteria in Vegetation Concrete Under Freeze-thaw Conditions

      LIU Daxiang, XU Zhihai, GAO Xian, XU Boyang, ZHENG Wei, XIA Dong, XU Wennian, YANG Yueshu

      2025,62(2):579-591, DOI: 10.11766/trxb202312110525

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      Abstract:

      【Objective】 This study aimed to isolate and identify autotrophic nitrogen-fixing bacteria in vegetation concrete under freeze-thaw conditions and to investigate their effects on the physical and chemical properties of vegetation concrete and the growth of ryegrass. 【Method】 Autotrophic nitrogen-fixing bacteria GDJ-1 and GDJ-2 were isolated from vegetation concrete that had experienced multiple freeze-thaw cycles by selective nitrogen fixation medium. The strains were identified by morphological, physiological, and biochemical characteristics, 16S rDNA, and phylogenetic analysis. The effects of target strains on physicochemical indexes of vegetation concrete and the growth of ryegrass were explored. 【Result】 Strain GDJ-1 was identified as Microbacterium proteolyticum, a Gram-positive bacterium with a round yellow colony. The strain GDJ-1 did not produce oxidase but was capable of producing catalase and it could not degrade gelatin or hydrolyze starch. This bacterium exhibited favorable growth under pH levels that ranged from 7 to 9 and in the presence of sodium chloride (NaCl) concentrations between 0.5% and 2%. After treatment with GDJ-1, the aboveground fresh biomass, aboveground dry biomass, belowground fresh biomass, and belowground dry biomass of ryegrass increased by 29.09%, 5.05%, 13.40%, and 16.40%, respectively, compared with the control group. The contents of organic matter, total nitrogen, alkali-hydrolyzed nitrogen, and available phosphorus in vegetation concrete were increased, and the increase of alkali-hydrolyzed nitrogen was 62.95%. Furthermore, strain GDJ-2 was Ralstonia pickettii, a Gram-negative bacterium with a round beige colony. The strain GDJ-2 produced oxidase but did not produce catalase, and was capable of hydrolyzing gelatin and starch. It exhibited favorable growth under conditions with a pH range of 7 to 9 and a sodium chloride (NaCl) concentration of 0.5% to 2%. After treatment with GDJ-2, the aboveground fresh biomass, aboveground dry biomass, belowground fresh biomass, and belowground dry biomass increased by 35.71%, 4.93%, 46.38%, and 13.79%, respectively, compared with the control group. The contents of organic matter, total nitrogen, alkali-hydrolyzed nitrogen, and available phosphorus in vegetation concrete were increased, and the increase of available phosphorus reached 35.73%. 【Conclusion】 There were great differences in morphology and enzyme metabolism between the two strains, but both were capable of enhancing the nutrient condition of vegetation concrete and promoting the growth of ryegrass. In the ecological restoration of vegetation concrete, autotrophic nitrogen-fixing bacteria GDJ-1 and GDJ-2 displayed application potential. GDJ-1 possessed a robust nitrogen fixation ability, effectively converting nutrients in the soil, which was more suitable for regions where the soil was poor or lacking nutrients. However, GDJ-2 demonstrated superior environmental adaptability, especially exhibiting heightened tolerance to alkaline environments, making it more fitting for regions with stringent conditions such as saline-alkaline soils. Considering the necessity for nutrient balance in actual engineering projects, further research can be conducted on freeze-thaw tolerant indigenous phosphate-solubilizing, potassium-releasing, and cellulose-decomposing bacteria, to develop a composite bio-agent tailored for vegetation concrete ecological restoration in freeze-thaw areas.

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      • The Mechanism of γ-MnO2-mediated Abiotic Nitrogen Mineralization in Peptone and Its Influencing Factors

        HONG Jun, XIA Xiange, CHEN Yunfeng, LIU Bo, DUAN Xiaoli, ZHANG Minmin, NIE Xinxing, YANG Li

        DOI: 10.11766/trxb202412050475

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        【Objective】Existing literature has predominantly concentrated on the influence of microbial activity on soil organic nitrogen mineralization. However, the role of abiotic processes, particularly the non-biological mineralization of organic nitrogen facilitated by typical manganese oxides, has received little attention. 【Method】This study employed nsutite (γ-MnO2) as the experimental mineral and soybean-derived peptone as a representative of soil organic nitrogen to investigate the effect of abiotic nitrogen mineralization mediated by γ-MnO? under a near-neutral environment and elucidated the reaction mechanism. Three experimental systems were designed: a peptone system (0.25 g?L–1), a γ-MnO2 system (1.0 g?L–1), and a mixed system comprising both peptone (0.25 g?L–1) and γ-MnO2 (0.25~2.0 g?L–1). 【Result】The results indicated that under pH 7.0 and in an air atmosphere, γ-MnO2 could facilitate the mineralization of peptone nitrogen, producing inorganic nitrogen. The mineralization rate of peptone (0.25 g?L–1) initially increased and then tended to stabilize with increasing initial γ-MnO? concentrations (0.0-2.0 g?L–1). In this process, Mn(IV) and Mn(III) present in γ-MnO?, along with reactive oxygen species (ROS) generated on the mineral surface, served as the principal oxidizing agents facilitating the mineralization of peptone into inorganic nitrogen. 【Conclusion】This study is anticipated to advance the understanding of organic nitrogen mineralization mechanisms in farmland soils and to enhance the comprehension of nitrogen cycling processes within agricultural ecosystems.

      • Spatiotemporal Distribution Characteristics of Soil Nitrification Rate and Influencing Factors in the Fen River Riparian Zone

        diyani, zhangyike, zhangzewen, wangchunling

        DOI: 10.11766/trxb202406110229

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        【Objective】The water-land ecotone is the last barrier to effectively intercept runoff nitrogen pollutants from entering the water body. Nitrification is a key process of soil nitrogen cycle, and studying the temporal and spatial distribution characteristics and influencing factors of soil nitrification rate in riparian water-land ecotone is helpful to understand soil denitrification in riparian water-land ecotone.【Method】In this study, the spatiotemporal distribution characteristics of soil nitrification rate and physicochemical properties in the riparian water-land ecotone of the Taiyuan section of the Fen River were studied by taking soil samples at different distances, depths and in seasons. By measuring and analyzing the nitrification rate and physicochemical indexes, the main driving factors affecting the soil nitrification rate in the riparian water-land ecotone were explored through Spearman correlation analysis, RDA ranking analysis, and structural equation model. 【Result】The results showed that: (1) The soil moisture content, organic matter, total nitrogen, ammonium nitrogen, and nitrate nitrogen in the water-land ecotone decreased as distance from the shore increased while the bulk density increased. Soil moisture content, electrical conductivity, organic matter, total nitrogen, ammonium nitrogen, and nitrate decreased with the increase in soil depth. Also, in summer, the average values of soil moisture content, bulk density, organic matter, total nitrogen, and nitrate were lower than those in autumn, while ammonium nitrogen was higher than that in autumn. (2) The soil nitrification rate increased first and then decreased with the increase in distance from the shore, and the nitrification rate of surface soil (20.43 mg·kg-1·d-1) was higher than that of the lower layer (8.97 mg·kg-1·d-1). In addition, the average soil nitrification rate in summer and autumn was 15.12 mg·kg-1·d-1 and 14.28 mg·kg-1·d-1, respectively. (3) Soil total nitrogen was the main influencing factor affecting the soil nitrification rate in summer in the water-land ecotone.【Conclusion】 In summary, the results of this study show that in the case of serious nitrogen pollution in river water, it is necessary to fully protect the water-land ecotone within 1 m of the waterbody, which will help improve the ability of riparian soil to intercept runoff nitrogen pollution, thereby protecting river water bodies. Thus, this study provides a scientific basis for the ecological construction, protection, and management of riparian ecotone.

      • Effects of Different Management Measures on Paddy Productivity and Phosphorus Balance in the Taihu Lake Lake Basin

        Chen Guanglei, Yue Ke, Yuan Jiahui, Zhu Yiyong, Kai Lei

        DOI: 10.11766/trxb202408030317

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        【Objective】This study aimed to evaluate the impact of various phosphorus (P) fertilizer application rates and irrigation methods on rice yield, P uptake, P loss, and P balance in the Taihu Lake Basin. The goal was to optimize nutrient management and mitigate non-point source pollution by assessing the effects of different P levels and water management practices on rice paddies. 【Method】The research applied a two-year field experiment with three P application rates (P2O5 0, 45, and 90 kg·hm-2) and three irrigation strategies: continuous flooding, mild dryness, and severe dryness. Soil and rice samples were collected at harvest. Soil P fractions were analyzed using sequential extraction, and rice yield and P uptake were measured from grain and straw. Runoff and leachate samples were obtained to assess P loss. 【Result】Compared to the control treatment (no phosphate fertilizer), applying P fertilizer increased rice yield by 2.20% to 11.5%. The P2O5 90 kg·hm-2 treatment reduced P agronomic and P use efficiencies by an average of 34.9% and 29.4%, respectively, compared to the application of P2O5 45 kg·hm-2. P application significantly increased the soil Olsen-P and available P fractions (the sum of Resin-P, NaHCO3-Pi, and NaOH-Pi) by 19.1%~62.4% and 36.5%~101%, respectively, while also enhancing P loss from paddy fields by 79.1% to 292%, compared to the control. In addition, the mild and severe dryness strategies significantly reduced P loss, with average decreases of 27.0% and 35.6%, respectively, particularly in runoff, where reductions were 31.5% and 41.3%, compared to flooding. The P2O5 90 kg·hm-2 treatment maintained a P balance for the rice season, while the application of P2O5 45 kg·hm-2 was sufficient to meet rice demands due to the high availability of soil P and Olsen-P higher than 20 mg·kg-1. Structural equation modeling indicated that Olsen-P and NaOH-Pi were the main influencing factors for rice yield, while Resin-P was the main influencing factor of P loss. 【Conclusion】Moderate P fertilization at P2O5 45 kg·hm-2 effectively increased rice yield with minimal P loss. Mild dryness irrigation and appropriate P application based on crop P requirements and soil P levels are vital for maximizing crop yields while minimizing P loss. The findings provide a scientific basis for nutrient management in paddy fields and the control of non-point source pollution in the Taihu Lake Basin.

      • The Influence of Straw Treatment Methods on Straw Mineralization and Priming Effects in Soil

        YANG Xin, ZHU Jun, REN Tao, LI Xiaokun, LU Jianwei

        DOI: 10.11766/trxb202406290265

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        【Objective】 The application of crop straw to soil is a popular strategy for managing cropland soil. However, the effects of pre-treatment of crop straw on its decomposition and priming effect in soil have received little attention. 【Method】 In this study, the structure, mineralization, and priming effect of pyrolyzed, biodegraded, and raw corn straw in the soil were investigated through an incubation experiment combined with the natural abundance approach. 【Result】 The results showed that the cumulative mineralization of straw materials in soil within 60 days followed the order biodegraded straw (1,945 mg kg-1), raw straw (1,576 mg kg-1), pyrolyzed straw (27 mg kg-1). The priming effect of pyrolyzed and raw straw on the mineralization of native soil organic matter was persistently negative and positive, respectively. Also, the priming effect of biodegraded straw changed from positive in the initial stage of incubation to negative in the latter period of incubation. Both raw and biodegraded straw significantly increased the abundance of fungi and the activities of β-glucosidase and cellulase in soil (P < 0.05), however, pyrolyzed straw did not significantly affect the fungal abundance and the activities of β-glucosidase and cellulase. High-throughput sequencing revealed that biodegraded straw significantly increased the relative abundance of Actinobacteria while raw straw significantly increased the relative abundance of Firmicutes (P < 0.05). 【Conclusion】 Because of low mineralization and negative priming effect, pyrolyzed straw showed higher potential than biodegraded and raw straw in the sequestration of soil organic carbon.

      • Changes of Community Diversity and Assembly Processes of Culturable Potassium-Solubilizing Bacteria in Soil under Different Enrichment Strategies

        Zeng Tao, Ba Mengya, Xia Weiwei, Zhang Yaohong, Cai Yuanfeng, Chen Xiao Fen, Jia Zhongjun

        DOI: 10.11766/trxb202406230255

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        【Objective】Potassium-solubilizing bacteria (KSB) are considered key plant growth-promoting bacteria for the sustainable development of ecological agriculture due to their unique advantage of potassium solubilization. To fully explore the resources of potassium-solubilizing bacteria in the environment, the changes in the characteristics of soil potassium-solubilizing bacterial communities were investigated in this study under various enrichment strategies. 【Methods】By using a potassium-solubilizing bacteria enrichment medium (KM),with a bacterial enrichment medium (BM) as a control, the study employed liquid (L) and solid (S) culture methods to continuously enrich and culture potassium-solubilizing bacteria in the test soil samples through three consecutive passages (1st, 2nd, and 3rd). The culturable microbial enrichments from each passage were collected, and high-throughput sequencing technology was used to analyze the 16S rRNA genes in the soil background and the enrichments. This analysis aimed to evaluate the proportion of culturable bacteria or potassium-solubilizing bacteria in the soil background bacterial community, as well as the community composition and diversity patterns under different enrichment strategies. 【Results】The results indicated that the bacterial diversity enriched by both media BM and KM was significantly lower than that in the background soil and the bacterial diversity in KM enrichments was significantly higher than that in BM enrichments. A total of 17 phyla, 38 classes, 91 orders, 145 families, and 267 genera of bacteria were detected in both L-KM and S-KM enrichments, with the most significant proportion at the phylum level accounting for approximately 29.31% of the soil background bacteria. The number of bacterial taxa enriched with L-KM medium was higher than S-KM at all levels. At the phylum level, the dominant phyla in L-KM were Firmicutes and Proteobacteria while in S-KM, the dominant phyla were Actinobacteriota and Proteobacteria. At the genus level, groups with distinct physiological and metabolic characteristics were enriched through three consecutive passages. Among them, the dominant genera in L-KM were Aminobacter, Chelatococcus, Cupriavidus, Hydrogenophilus, Microvirga, Paenibacillus, and Phenylobacterium. The only genus in S-KM that overlapped with L-KM was Cupriavidus, while other dominant genera included Burkholderia, Luteibacter, Massilia, Pseudomonas, and Ralstonia. Compared with known potassium-solubilizing bacteria databases, only 50 known genera were enriched in the KM medium, while unknown potassium-solubilizing bacteria accounted for over 81%. Using null model inversions to analyze the bacterial community assembly process during continuous passaging enrichment under different media, it was found that deterministic processes dominated the changes in community structure from the soil suspension inoculation to the first-generation media, while stochastic processes, mainly genetic drift, governed the intergenerational bacterial community succession. 【Conclusion】These results indicate that the composition and form of the medium are the main factors influencing the culturable potassium-solubilizing bacterial community, but continuous passaging enrichment does not lead to homogenization and simplification of the community structure. A relatively large number of both known and unknown potassium-solubilizing bacterial genera can be obtained under different enrichment strategies and used to enrich the existing resource bank of potassium-solubilizing bacteria. This can provide valuable insights for further development and utilization of these bacteria.

      • The Relationship Between Microbial Necromass Carbon and Soil Aggregate Stability on a Global Scale

        Kuang Yanyun, Hu Han, Li Sen, Liang Yuting

        DOI: 10.11766/trxb202409030355

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        【Objective】 The soil organic carbon (SOC) pool is the largest carbon reservoir in terrestrial ecosystems, playing an essential role in mitigating climate change and maintaining soil fertility. Among the various components of SOC, microbial necromass carbon (MNC) constitutes a significant proportion, contributing approximately 30-80% to the total SOC, and playing a crucial role in stabilizing soil carbon stocks. Accumulation and stabilization of MNC in soil are closely linked to the formation and stability of soil aggregates, which provide physical protection against microbial decomposition. Despite the known connection between MNC and soil aggregation, no comprehensive studies have systematically explored the relationship between MNC and soil aggregate stability. This study aims to further explore the global association between MNC and soil aggregate stability.【Method】 To assess the relationship between MNC and soil aggregate stability, we compiled global observational datasets on soil amino sugars (biomarkers of MNC) and soil aggregates. Using machine learning techniques, we predicted the global distribution of MNC and analyzed its correlation with the stability of soil aggregates. The PLS-PM was employed to further investigate the pathways through which soil aggregate stability influences MNC sequestration, takin into account factors such as soil physical properties, nutrient availability. 【Result】 The results revealed that MWD is a key predictor of MNC, with a significant positive correlation between MNC and MWD on a global scale (P < 0.05). Further correlation analysis of global prediction data confirmed this relationship and showed that it is consistent across different ecosystems. The Partial Least Squares Path Model (PLS-PM) analysis revealed that soil aggregates protect MNC directly by forming physical barriers and indirectly by regulating soil physical properties and nutrient availability, which in turn influence MNC accumulation and stabilization. In particular, soil nutrients had the most significant positive impact on MNC (path coefficient = 0.67, P < 0.05). The process through which MWD influences MNC shows significant differences across different ecosystems, specifically in terms of the direction and strength of the pathways. For example, in agricultural ecosystems, the indirect effects through soil physical properties and nutrients are more pronounced, while in forest ecosystems, the direct effect is stronger. 【Conclusion】The findings of this study underscore the significant role of soil aggregates in stabilizing MNC, and highlight the potential of soil aggregation as a key factor in enhancing soil carbon storage. Also, the positive correlation between MNC and aggregate stability suggests that strategies aimed at improving soil structure; eg., practices that enhance aggregation and optimize nutrient management, can effectively contribute to greater carbon sequestration. By fostering more stable soil aggregates, we can improve MNC sequestration, mitigate climate change, and sustain soil fertility. Furthermore, these findings can inform the development of predictive models for MNC sequestration and the integration of soil aggregate stability as a critical indicator for assessing the carbon sequestration potential of soils.

      • Effects of Different Mulching Treatments on Soil Microbial Diversity and Community Structure in Rhizosphere Soil of Maize Under the “Dryland Triple Intercropping” System

        SONG Lixia, WU Xinyao, SONG Wenfeng, REN Ke, LIU Bangyan, ZHEN Yuzhuo, LIU Ming, ZHOU Yuling, LIU Chaoji, WANG Longchang

        DOI: 10.11766/trxb202405220207

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        【Objective】This study aimed to investigate the effects of different mulching treatments on microbial diversity and community structure of maize rhizosphere soil under the planting mode of “dryland triple intercropping”. 【Method】It was conducted a two-year randomized block group field experiment with four treatments: no mulching (control), straw mulching (S), milk vetch mulching (M), and combined mulching of straw and milk vetch (S+M). Sequencing of internal transcribed spacer region (ITS) rDNA and 16S rRNA genes using Illumina MiSeq PE300 high-throughput technology was used to analyze changes in microbial characteristics of maize soils at the flowering stage after mulching. 【Result】The main results were as follows: (1) The M and S+M treatments decreased the number of soil bacterial species and community diversity, the S and S+M treatments increased the number of soil fungal species and community diversity, while the M treatment decreased the number of soil fungal species. The differences in soil bacterial composition and community structure between the mulched treatments (S, M, S+M) and the no-mulch treatment were significant; fungal communities were not interspersed with each other, differed significantly, and did not have similar community composition between treatments. (2) Mulching treatments decreased endemic bacterial species whereas S and S+M treatments increased fungal species endemic to each treatment. Compared with the control treatment, the mulching treatment increased the relative abundance of Proteobacteria, Actinobacteria, and Basidiomycota in the dominant bacterial phyla of the rhizosphere soil of maize, and decreased the relative abundance of Acidobacteria and Ascomycota. (3) The S+M treatment affected the bacterial microbial community structure by influencing total phosphorus and nitrate nitrogen, which were positively correlated with dissolved organic carbon and readily oxidizable carbon, while the M and S+M treatments affected the fungal microbial community structure by influencing total nitrogen and nitrate nitrogen, which were positively correlated with soil water content, available phosphorus, total nitrogen and nitrate nitrogen.【Conclusion】Compared to the control treatment, the mulching treatments were able to improve soil microbial diversity and community structure, accelerate the decomposition of straw and milk vetch in the field to promote the absorption and utilization of soil nutrients by maize, and positively contribute to the soil ecological balance. Of all the treatments, the synergistic mulching treatment of straw and milk vetch was the most effective. Therefore, synergistic mulching treatment with straw and milk vetch is an effective measure for conservation tillage in the drylands of Southwest China.

      • Study on the Coupling Mechanism Between Soil Bacterial Community Diversity and Ecosystem Multifunctionality in Intensive Citrus Cultivation Systems

        HU Man, ZENG Quanchao, ZHOU Quan, ZHOU Lianhao

        DOI: 10.11766/trxb202404150156

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        【Objective】Intensive monoculture practices can degrade land, but the specific impacts of long-term, high-intensity citrus cultivation on soil microbial communities and soil multifunctionality are not well understood.【Method】This study examined soils from citrus orchards of varying planting durations, using high-throughput sequencing to assess the influence of intensive cultivation on soil microbial communities. It also investigated soil multifunctionality, microbial diversity, and co-occurrence networks associated with carbon, nitrogen, and phosphorus cycling. 【Results】This study indicated that soil bacterial diversity declined significantly as the duration of citrus cultivation increases. The Shannon index decreased from 7.05 in 5-year soils to 5.79 in 30-year soils, with species numbers dropping from 2 110 to 1 153. Microbial network complexity was also reduced in 30-year soils, with fewer taxa and fewer inter-taxa associations than in 5-year soils. Network nodes declined from 1 491 to 815, and edges from 8 449 to 2 369. Network complexity and stability varied significantly across citrus ages, with younger (5-year) soils showing greater complexity and stability than older (30-year) soils. Also, long-term citrus cultivation led to soil acidification, altering bacterial activity, community structure, and species composition. This included an increase in dominant taxa like Proteobacteria, Actinobacteria, and Firmicutes, and a decline in Acidobacteria, Chloroflexi, and Gemmatimonadetes. The relative abundance of nitrogen-cycling bacteria also increased, supporting processes such as nitrogen fixation, aerobic ammonia oxidation, denitrification, and aerobic nitrite oxidation. Changes in microbial diversity and structure correlated closely with shifts in soil multifunctionality, influenced by high-intensity citrus cultivation. The number of microbial network nodes showed a negative correlation with carbon cycle multifunctionality (CMF) and positive correlations with nitrogen cycle (NMF) and phosphorus cycle multifunctionality (PMF). The number of edges correlated negatively with CMF, positively with NMF, and was not significantly associated with PMF. 【Conclusion】Microbial diversity drives the complexity of microbial co-occurrence networks, significantly correlating with the number of network nodes and edges. Collectively, these findings indicate that prolonged citrus cultivation significantly reduces soil microbial diversity and impairs multiple ecological functions.

      • Differences in Mineral-Associated Organic Carbon and Particle Organic Carbon Mineralization in Typical Grassland Soils

        YUAN Chenyang, YANG Renmin, FU Zihuan, CHEN Shiping, YAN Zhifeng

        DOI: 10.11766/trxb202410060383

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        【Objective】The mineralization process of soil organic carbon (SOC) and its components is complex. For example, particulate organic matter (POM) and mineral-associated organic matter (MAOM) are two components with different physicochemical properties and turnover rates. However, few studies have paid attention to the differences in the response of these different components to climatic factors. Thus, this study aimed to investigate the differences in the mineralization of POM and MAOM under different temperatures and moisture conditions and provide a basis for the estimation and prediction of CO2 emission fluxes in the context of global climate change. 【Method】The soil of Xilingol grassland in Inner Mongolia was collected to obtain POM and MAOM using a physical grading method and controlling the same mass of each fraction. Bulk soil was incubated under optimum conditions for 180 days, and POM and MAOM were incubated at different temperature and moisture conditions for 60 days to investigate the differences in mineralization of the two fractions and their response to temperature and moisture. 【Result】After 180 days of incubation experiments under optimal conditions, the cumulative CO2 emission from the grassland soil reached 2688 mg kg-1. MAOC in the grassland soil was relatively large, which accounted for 60% to 75% of TOC. Under different temperature conditions, the mineralization rates of both POM and MAOM increased with increasing temperature, while the two fractions responded differently to soil moisture content. There was a positive but insignificant correlation between the CO2 emission rate of MAOM and soil moisture, while there was no significant correlation between the CO2 emission rate of POM and soil moisture. It was also found that MAOM was much larger than POM in terms of cumulative CO2 emissions per unit of soil mass, while POM was much larger than MAOM in terms of cumulative CO2 emissions per unit of organic carbon. 【Conclusion】The mineralization of grassland soils MAOM and POM showed significant differences in response to temperature and moisture, suggesting that the mechanisms controlling the mineralization of these two carbon pools are different. The cumulative CO2 emission per unit of organic carbon in POM was much larger than that in MAOM, suggesting that the carbon in POM is more easily mineralized under the same conditions. Thus, distinguishing between POM and MAOM helps to better understand SOC turnover and provides a scientific basis for improving the SOC mineralization model.

      • Global Spatial Distribution and Driving Factors of Soil Microbial Necromass Carbon Stability

        ZHENG Hongfeng, ZHAO Yuan, HU Han, LI Sen, ZHANG Li, LIANG Yuting

        DOI: 10.11766/trxb202410150397

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        【Objective】Microbial necromass carbon plays a significant role in the global carbon cycle and is a key contributor to soil organic carbon. Its importance stems from its stability, which is crucial for carbon protection and long-term carbon storage in soils. Within microbial necromass carbon, fungal necromass carbon (FNC) and bacterial necromass carbon (BNC) are two main components, and research has shown that FNC is more stable than BNC. Therefore, a higher proportion of FNC relative to BNC, expressed as the FNC/BNC ratio, is often considered indicative of greater microbial necromass carbon stability. However, despite the recognition of this relationship, the global distribution patterns of microbial necromass carbon stability and the factors influencing these patterns remain unclear due to a lack of large-scale observational data. Addressing this gap is essential for advancing our understanding of the mechanisms behind soil carbon cycling and protection.【Method】To address these uncertainties, this study employs a combination of meta-analysis and machine learning techniques to analyze microbial necromass carbon stability on a global scale. Meta-analysis allows for the synthesis of findings from multiple studies to produce more robust conclusions, while machine learning enables the identification of complex patterns in large datasets. Together, these methods offer a powerful approach to uncovering the spatial distribution of microbial necromass carbon stability and its driving factors. The study specifically examines the relationship between FNC/BNC ratios and various environmental variables, including soil nutrient levels (such as soil organic carbon, total nitrogen, and total phosphorus) and climatic factors (such as annual mean temperature and evaporation). By analyzing data from different ecosystems and climatic zones, the study aims to clarify the global patterns of microbial necromass carbon stability and the key factors influencing it.【Result】The results showed that the global average stability of microbial necromass carbon was 3.09. Among different ecosystems, forests had the highest average value (3.94), while deserts had the lowest (1.09). In terms of climate zones, the highest average value was found in the polar regions (4.14), and the lowest in arid climate zones (1.69). In different aridity index regions, the stability of microbial necromass carbon was lowest in extremely arid areas (0.75) and highest in semi-humid regions (3.77). Also, microbial necromass carbon stability exhibits distinct characteristics across different regions.【Conclusion】Overall, microbial necromass carbon stability tends to be lower under conditions of higher annual mean temperature or greater annual evaporation, indicating a negative correlation between climatic conditions and microbial necromass carbon stability. Soil organic carbon, total nitrogen, and microbial biomass nitrogen were identified as key regulators of microbial necromass carbon stability, with positive correlations to its stability. Moreover, annual mean temperature and evaporation indirectly affected microbial necromass carbon stability by influencing the levels of soil organic carbon, total nitrogen, and total phosphorus. The study highlighted the global spatial distribution of microbial necromass carbon stability and the major driving factors behind it. These findings provide valuable theoretical support for developing soil management strategies that focus on protecting and enhancing organic carbon based on the stability of necromass. Such strategies can help maintain and improve soil health, carbon sequestration, and ecosystem functioning in the face of changing environmental conditions.

      • The influence of mycorrhizal types on the soil microbial biomass carbon and its distribution

        MA Zhenyi, SUN Yichun, SHI Zhaoyong, GAO Jiakai, WEI Wenjing

        DOI: 10.11766/trxb202406120230

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        【Objective】Soil microbial biomass carbon (SMBC) is an important indicator of microbial activity, and the type of mycorrhizal has a potential impact on SMBC content. The objective is to explore the impact of different mycorrhizal types on soil microbial biomass carbon and clarity their functions under global climate changes. 【Method】Based on the SMBC database established by predecessors, the SMBC content and its distribution of plants of different mycorrhizal types were explored by dividing different soil layers (0-100 cm, 0-40 cm, 40-100 cm) and determining the mycorrhizal types of plants in the database. 【Result】The results showed significant differences in SMBC between different layers of Arbuscular mycorrhiza (AM) and Ectomycorrhiza (ECM) plants, among which ECM plant soil SMBC was significantly higher than that of AM plant. There were also differences in the response of SMBC to soil parameters (soil depth, soil total nitrogen) and climate parameters (average annual temperature, average annual rainfall). At soil depth of 0-40 cm, the effects of factors (48.9%, 47.99%) on SMBC were significantly higher than that of climate factors under both AM and ECM plants (8.45%, 2.25%). Also, at soil depth of 40-100 cm, the SMBC of the ECM plant was more affected by climate factors (53.94%) than soil factors (25.32%), while the AM plant was affected differently, with the soil factor (45.17%) showing a more significant effect than climate factors (25.32%). 【Conclusion】Under the influence of different types of mycorrhiza, SMBC was significantly positively correlated with soil organic carbon and total nitrogen (P<0.01), among which ECM was more affected by soil organic carbon and total nitrogen. The analysis of variance decomposition found that with the increase in soil depth, AM plant SMBC in deep soil was mainly affected by soil factors, while ECM plant SMBC was mainly affected by climate factors. In summary, the SMBC content of the ECM plant was significantly higher than that of the AM plant, and the response to organic carbon and soil total nitrogen was also higher than that of the AM plant.

      • Effects of Different Organic Materials on the Stability of Saline-alkali Soil Colloid

        SUN Yuliang, LI Qirui, Li Wei, Wang Xiang, SHANG Jianying

        DOI: 10.11766/trxb202408300349

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        【Objective】Soil colloid stability plays an important role in soil nutrient retention, structure formation and crop growth. The application of organic materials is an effective method for improving saline-alkali soil, but their effects on soil colloid stability in these conditions remain unclear.【Method】In this study, we investigated the effects of biochar (BC), cattle manure (CM), and maize straw (MS) on soil colloid stability at different salinity-alkalinity levels (non-saline-alkali, mild saline-alkali and moderate saline-alkali) through soil incubation and sedimentation experiments in the laboratory.【Result】(1) The addition of organic materials significantly reduced the diameter of saline-alkali soil colloidal particles, making it similar to the diameter of non-saline-alkali soil colloid. In mild saline-alkali soil, the effect of MS treatment was most effective, and the colloidal particles size decreased from 785.7 nm to 360.2 nm. In moderate saline-alkali soil, the effect of CM treatment was most effective, decreasing the colloidal particles size from 675.8 nm to 393.6 nm. (2) The stability of soil colloid is related to the degree of soil salinity. Compared with non-saline-alkali soil and mild saline-alkali soil, moderate saline-alkali soil colloid exhibited significantly high stability, likely due to elevated high pH and high alkalinity. (3) Organic materials had minimal effect on the colloid stability of non-saline-alkali soil and mild saline-alkali soil. However, CM and MS treatments significantly reduced the colloid stability of moderate saline-alkali soil, causing colloidal particles agglomerated. Therefore, in moderate saline-alkali soil, the application of cow manure and maize straw may be more effective than biochar for stability improvement.【Conclusion】The application of organic materials ameliorates the basic physicochemical properties of saline-alkali soil and optimizes the state of soil colloid. Compared with biochar, cattle manure and maize straw, due to their rich functional groups and nutrients, significantly reduced the colloid stability of moderate saline-alkali soil upon application, thereby inducing colloidal aggregation and promoting the formation of microaggregates.

      • The Contribution of Microbial Necromass Carbon and Its Influencing Factors in Biocrust-Covered Soils in the Mu Us Desert

        mengyanrong, Baicunlin, Zhao guangwei, Niuxiangwen, SheWeiwei, ZhangYuqing, QinShugao, Yang Jing, Jiang Ya Wen, Li Ming Jie, FengWei

        DOI: 10.11766/trxb202404240168

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        Abstract:

        Abstract: 【Objective】Biocrusts are critical surface covers in desert ecosystems that play an essential role in enhancing soil organic carbon (SOC) sequestration through various biological and physicochemical processes. Despite extensive research on biocrust functions, the contribution of microbial necromass carbon (MNC) under biocrust (BSCs) coverage to SOC and its influencing factors remains unclear. This study aims to address this knowledge gap by analyzing the role of cyanobacterial, lichen, and moss crusts in the Mu Us Desert.【Method】Soil samples were collected from the cyanobacterial, lichen, and moss crust layers, as well as from the underlying soil (0–5 cm depth), to investigate their physicochemical properties and amino sugar contents as proxies for MNC. Contributions of fungal necromass carbon (FNC) and bacterial necromass carbon (BNC) to SOC were evaluated, and their relationships with soil pH, nitrogen content, exchangeable calcium ions, soil moisture, and particulate organic carbon (POC) versus mineral-associated organic carbon (MAOC) fractions were assessed.【Result】The results revealed that: (1) MNC constituted approximately 57.7%, 47.9%, and 22.5% of SOC in cyanobacterial, lichen, and moss crusts, respectively, while in the underlying soil, MNC contributed 40.7%, 40.2%, and 28.5% of SOC for the respective crust types. (2) Across all crust types, FNC contributed significantly more to SOC than BNC, with average contributions of 28.4%±10.7% and 11.2%±4.8%, respectively. (3) MNC, especially FNC, had a stronger influence on the POC fraction compared to MAOC, suggesting its dominant role in labile carbon pools. (4) Positive correlations were found between FNC and BNC and soil nitrogen contents (ammonium, nitrate, and total nitrogen) as well as SOC. Conversely, significant negative correlations were observed with soil pH, exchangeable calcium ions, and moisture content. These findings indicate that soil properties strongly regulate the dynamics of MNC in biocrust-covered soils. (5) The spatial variability of MNC contributions highlights the critical role of crust type and underlying soil characteristics in shaping microbial-derived SOC.【Conclusion】This study highlights that the contribution of MNC to SOC diminishes from cyanobacterial to lichen to moss crusts, with FNC consistently being the dominant component. MNC primarily contributes to the POC fraction, underscoring its role in maintaining active carbon pools. Soil nitrogen content, SOC, pH, exchangeable calcium ions, and soil moisture emerged as key factors influencing the accumulation and decomposition of MNC. These insights enhance our understanding of microbial-mediated soil carbon cycling and sequestration mechanisms in arid ecosystems. Furthermore, the findings underscore the importance of preserving biocrust integrity to sustain carbon storage functions in desert landscapes. The results provide a scientific foundation for devising carbon management strategies aimed at mitigating desertification, enhancing carbon sequestration, and fostering sustainable development in desert regions.

      • Extraction of Biofilms and Mineral Response Characteristics of Interspecific Interaction in Acidic Purple Paddy

        Yan Guili, Wen Yi, Zhao Sheng, Xiong Xuan, Liu Shanpeng, Jiang Yu, Tang Yuqing, OUYANG Kai

        DOI: 10.11766/trxb202406210252

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        【Objective】Soil minerals, as the main carrier of biofilms, regulate the formation of multi-species biofilms in soil and profoundly affect the types of bacterial interactions within the biofilm.【Method】To further reveal the interaction mechanism between soil active components and multi-species biofilms, this study selected common minerals such as kaolinite, montmorillonite, and goethite in soil, as well as strains extracted from paddy soil, as research objects. Single strains were paired and co-cultured with soil minerals. In situ monitoring was carried out using confocal laser scanning microscopy (CLSM) combined with the crystal violet staining method, to explore the formation of multi-species biofilms and the response of bacterial species interactions within biofilms to soil minerals.【Result】The results show that compared with the pure bacterial system, both kaolinite and montmorillonite treatments significantly inhibited the formation of multi-species biofilms, and the S-1+S-14 combination in the kaolinite treatment system was most inhibited, with a decrease of 42.57% in biofilm biomass. The addition of kaolinite changed the interaction between the S-1+S-2 strain combination from synergistic to neutral and adjusted the S-1+S-8 combination from neutral to antagonistic. However, montmorillonite alleviated the antagonistic interaction between the S-1+S-14 and S-1+S-15 strains, and their interaction relationship shifted to neutrality. The treatment of goethite significantly promoted the formation of multi-species biofilms in the four groups, with the S-1+S-14 combination showing the greatest increase in biofilm biomass (46.45%). Also, the addition of goethite significantly enhanced the synergistic effect of the S-1+S-2 mixed microbial community, causing the interaction between microbial communities in the S-1+S-8 and S-1+S-14 combinations to shift from neutral and antagonistic to synergistic, and adjusting the S-1+S-15 combination from antagonistic to neutral.【Conclusion】This study clarifies the effects of different types of soil minerals on the formation of multi-species biofilms and reveals the potential mechanisms for the transformation of interactions between microbial communities within biofilms. The results of this study can provide theoretical guidance for a deeper understanding of the microbial effects of soil components and soil biological processes, as well as further exploration of soil biological resources.

      • Effects of Different Types of Vegetation Restoration on Soil Pore Characteristics in Benggang Erosion Areas

        WANG Qiankun, ZHANG Xin, YANG Wei, PENG Jue, WANG Junguang

        DOI: 10.11766/trxb202408270344

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        【Objective】This study aimed to investigate the impact of different vegetation restoration types on soil pore characteristics in Benggang areas.【Method】Surface soil samples were collected from four vegetation-restored lands (artificial arbor, artificial forest, artificial shrubland, and artificial grassland) in the Benggang erosion area and an unplanted site was selected as the control (eroded land). The pore characteristics of the aggregates (3~5 mm) were visualized and quantified using X-ray microcomputed tomography (μCT) at a voxel resolution of 5.91 μm. Following the imaging, we measured various physical soil hierarchies, including bulk density, aggregate size distribution, and mechanical composition across multiple scales. 【Result】The results indicated that vegetation restoration significantly improved the formation and stability of soil aggregates, leading to notable changes in aggregate pore characteristics and characterized by high anisotropy and fractal dimension. This suggests that different vegetation types not only influence the physical properties of the soil but also enhance its ability to retain water and nutrients, thereby contributing to overall soil structure. The aggregate pore size distribution varied among the different revegetated sites, reflecting the influence of specific environmental conditions and management practices associated with each type of vegetation. The Soil Structure Index (SSI) was used to assess the overall quality of soil structure. The findings revealed that, except for artificial grassland, the SSI values were consistently higher for all vegetation-restored lands compared to the eroded land. The ranking of SSI values followed artificial arbor (0.66) > artificial forest (0.60) > artificial shrubland (0.48) > eroded land (0.31)> artificial grassland (0.25). This hierarchy underscores the significant benefits of arboreal woodlands, particularly citrus orchards, in enhancing soil structure and stability. 【Conclusion】Overall, the results of this study underscore the critical role of vegetation restoration in promoting ecological recovery and improving soil quality in the Benggang erosion areas of South China. By demonstrating the positive impacts of different vegetation types on soil aggregate pore characteristics, this research provides valuable insights for land management and ecological restoration efforts. Future studies could expand on these findings by exploring the long-term effects of various restoration practices on soil health and erosion control, thereby contributing to more effective strategies for sustainable land use and environmental conservation.

      • Effects of Different Organic Fertilizers on the Formation, Stabilization, and Turnover of Aggregates in Acidic Soil

        ZHANG Jie, ZHOU Jia, WANG Yongmin, SHI Xiaojun, WANG Shuai, YU Haiyan, XU Qingwei, CHANG Xia, WANG Zeyu, YE Sili, HUANG Haiyang, ZHANG Yuting

        DOI: 10.11766/trxb202407230298

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        【Objective】Acidic soil is not conducive to the formation of water-stable macroaggregates, which in turn affects the level of soil fertility and the normal growth of crops. Research suggests that the application of organic fertilizer is an important way to improve acidic soils, however, the effect of organic fertilizers on the formation processes of acidic soil aggregates remains not clear. Also, there is a lack of evaluation and comparison between different types of organic fertilizers. 【Method】The rare earth oxide tracer method was used to test different organic fertilizers with equal carbon content on purple and red soil for 56 days. Four treatments were set up (no organic fertilizer control as CK; ordinary organic fertilizer as OF; biochar organic fertilizer as BC; and bio-organic fertilize as BO) and used to determine the stability of soil aggregates, the content of organic carbon in each fraction of aggregates, soil respiration, and the turnover path and rate of aggregates.【Results】The results showed that compared with the CK, the addition of organic fertilizer effectively reduced the amount of aggregate fragmentation, promoted the turnover and formation of large aggregates (>0.25 mm), and increased the average weight diameter (MWD) of soil aggregates. The BO treatment had the best effect on improving the stability of soil aggregates, which could be increased by 53.5%～103.35%. Adding organic fertilizer promoted the formation of the 0.25 mm aggregates and by calculating the turnover rate of soil aggregates, it was found that the addition of organic fertilizer reduced the turnover rate of large aggregates and increased the turnover rate of small aggregates (<0.25 mm). It is worth noting that in purple soil, the turnover rate of small aggregates was higher than that of large aggregates, while in red soil, the opposite trend was observed. Also, the addition of organic fertilizer promoted soil respiration and significantly increased the content of organic carbon in individual fractions (P<0.05). The total organic carbon content of different treatments was BC > BO > OF > CK, which increased by 14.50%～27.78% in purple soil and only increased by 6.40%～9.82% in red soil. 【Conclusion】In general, the application of organic fertilizer can effectively reduce the fragmentation process of aggregates, promote the turnover of small aggregates to large aggregates, and improve the stability of aggregates. The application of bio-organic fertilizer was more conducive to improving the level of soil water-stable macroaggregate structure, increasing soil stability, and improving soil structure.

      • Research Hotspots Analysis of Typical Halogenated Flame Retardants in Soil Environment Based on Knowledge Graph

        XUAN Yujie, ZHU Min†, WU Junhao, FENG Yao, SHENTU Jiali, LÜ Li, LONG Yuyang, SHEN Dongsheng

        DOI: 10.11766/trxb202405010180

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        【Objective】The extensive use of halogenated flame retardants has raised serious ecological and health concerns. Soil as the primary contamination sink for halogenated flame retardants has riased wide concern among many scholars.【Method】To understand the current state and emerging trends in the study of halogenated flame retardants in soil environments, a systematic review was conducted using knowledge mapping tools, VOSviewer and CiteSpace, on 2259 research articles published between 2008 and 2023 from the Web of Science Core Collection database.【Result】The findings reveal the following: (1) The number of publications on halogenated flame retardants in soil environments has steadily increased in the past sixteen years, with Environmental Ecology as the dominant research discipline. Over the research period, China was the dominant country with the largest number of research publications; (2) Key journals in the field include Science of the Total Environment, Chemosphere, and Environmental Science & Technology, with core authors such as Li Jun, Zhang Gan, and Jiang Guibin forming a closely-knit research network; (3) The content of halogenated flame retardants in the soil of China""s economically developed regions, especially the Pearl River Delta, Yangtze River Delta and Bohai Rim region, is significantly higher than that of other regions; (4) Halogenated flame retardants in the environment have led to bioaccumulation and biomagnification, causing adverse effects on organisms; (5) Halogenated flame retardants have been widely detected in human bodies, with dietary intake and dust exposure being the primary routes of human exposure; (6) The migration behavior of emerging brominated and chlorinated flame retardants in the environment and the health risk assessment are current hotspots trends in the current research.【Conclusion】This study conducted a comprehensive bibliometric analysis of research on halogenated flame retardants in soil environments. The environmental behavior and ecological health risks of halogenated flame retardants in soil have been receiving increasing attention, particularly in economically developed regions with severe pollution. Future research should focus on the transformation mechanisms and ecological effects of halogenated flame retardants in complex environmental matrices, especially the long-term effects of some emerging halogenated flame retardants, and provide a scientific basis for more effective management policies.

      • Research Progress on the Mechanism and Related Application of Soil Bio-driven Aggregates Formation and Stability

        MA Zheng, LI Zhenlun, YANG Yuran, LI Jiabing, ZHANG Xinlei, YANG Luyao, GUO Ruiting

        DOI: 10.11766/trxb202407270307

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        Abstract:

        Soil aggregates are an important component and basic unit of soil structure, and their stability is crucial for maintaining soil health and crop productivity. The formation and stability of aggregates are the result of the joint action of biological and non-biological factors, and soil organisms (microorganisms and animals) play a crucial role in this process. A thorough understanding of the relationship between soil organisms and the formation and stability of aggregates is of great theoretical significance in elucidating the process and mechanism of soil quality change. However, systematic summaries of the driving mechanisms and current application status of soil organisms in aggregate formation and stabilization are still lacking. This paper reviews the effects of soil microorganisms and animals on aggregate formation and stabilization and clarifies the aggregate formation process and stabilization mechanisms driven by soil organisms. The study discovers that microorganisms mediate aggregate formation and stabilization through their physical characteristics, secretion of adhesive substances, and decomposition of organic matter, while animals mediate aggregate formation and stabilization through biological disturbance and feeding. Furthermore, the current status of using soil organisms and their products to increase aggregate stability is analyzed, emphasizing the potential application of novel soil biological structural modifiers. In conclusion, prospective research directions are outlined for future investigations. Researchers should concentrate on the following areas: (1) The formation and stabilization mechanism of soil aggregates driven by soil organisms on multi-scale interface processes; (2) The composition and genetic regulation mechanism of microbial extracellular polymeric substances (EPS) and glomalin-related soil protein (GRSP); (3) The influence mechanism of soil archaea and viruses on the formation and stability of aggregates; (4) The formation process and stabilization mechanism of aggregates mediated by soil food web; and (5) Development and application of biological soil structure improvers. This paper aims to provide both theoretical insights and technical guidance for maintaining and improving soil quality.

      • Construction and application of synthetic communities: a new strategy to improve soil health

        Fang Linchuan, Hu Ziying, Cui Qingliang, Yang Yang, Liang Yuting, Cai Peng, Qu Chenchen, Gao Chunhui, Jiao Shuo, Liu Yurong, Huang Qiaoyun, Tan Wenfeng

        DOI: 10.11766/trxb202410120392

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        Abstract: Soil health is an important prerequisite to ensuring food security and maintain the services and functions of terrestrial ecosystems. Soil microorganisms play a key role in regulating nutrient circulation, enhancing rhizosphere immunity, and preventing environmental pollution. Rational development and application of microbial resources is an important means to protect soil health and exert soil functions in the future. However, the heterogeneity and complexity of soil ecosystems limit the identification and utilization of microbial functions. Currently, the development of synthetic biology provides new ways and ideas for using microorganisms to promote soil health. By fully exploiting the metabolic diversity, functional stability, environmental adaptability of microbial communities, and rationally constructing synthetic communities, technical support can be provided for the ecological restoration of soil damaged by environmental pollution or degraded in quality due to agricultural use. This review summarizes the approaches, tools, and application scenarios for constructing synthetic communities and explores their mechanisms in remediating contaminated soils, enhancing soil fertility, and promoting plant resistance to soil-borne diseases and abiotic stresses. Furthermore, future research directions are proposed, including the construction of synthetic community repositories, the development of synthetic biology tools, and the application of artificial intelligence for screening synthetic communities. These strategies are of great significance for achieving precise construction and directional utilization of synthetic communities in a specific range to improve soil health and ensure sustainable use of soil.

      • The Effects of Changes in Soil Humus Structure in Red Soil Orchards with Different Cultivation Ages on the Adsorption of Imidacloprid

        Zhang Yawen, Zhang Qin, Liu Can, Chen Junquan, Zhou Kai, TU SHUxin, Peng Xinhua, Guo Xinchun, Zheng Taihui

        DOI: 10.11766/trxb202406020069

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        【Objective】Neonicotinoid pesticides are one of the most commonly used insecticides in citrus orchards in the hilly areas of southern China. The long-term fertilization of orchards can alter the content and structure of soil organic matter, which in turn affects the adsorption behavior of pesticides in the soil. Therefore, gaining an in-depth understanding of the adsorption behavior of a typical neonicotinoid pesticide (imidacloprid) on soil humus in orchards is crucial for improving our knowledge of the environmental behavior of this class of pesticides in soil. This will provide a theoretical basis for preventing and controlling pesticide surface pollution at its source.【Method】Humic acid (HA) fractions (F1 to F10), low carbon humin (HuL) and high carbon humin (HuH) were extracted from soils (0~20 cm) with different cultivation chronosequences (10, 30 and 50 years). Adsorption isotherm experiments of imidacloprid on these humic fractions were conducted. 【Result】The adsorption isotherms of imidacloprid by humic acid (HA) fractions (F1~F10), and HuL and HuH fractions all fit the Freundlich model well, with R2 greater than 0.9. The adsorption affinity of humic acid for imidacloprid is about 100 times higher than that of HuL and HuH. The Kd values of imidacloprid ranged from 523.1 to 5 276L?kg-1, 543.3 to 5 717 L?kg-1, and 520.2 to 5 980 L?kg-1 at Ce of 0.5, 2.0, and 3.0 mg?L-1, respectively. All of them increased slightly with the increase of planting years. The KOC values of imidacloprid were positively correlated with aromatic C and negatively correlated with alkyl C of HA fractions (F1~F10). Also, the carbonyl C and carboxyl C of HuL were the key carbon functional groups controlling imidacloprid adsorption, while the alkyl C of HuH was the key carbon functional group controlling imidacloprid adsorption. 【Conclusion】Therefore, long-term cultivation can improve the adsorption of imidacloprid by humic substances to a certain extent, and the aromatic carbon structure of humic acid is the key structure regulating the adsorption of imidacloprid while the aliphatic carbon structure of humin is the key structure regulating the adsorption of imidacloprid.

      • Response of Soil Moisture Storages and Soil Carbon Stocks to Typical Patterns of Farmland Shelterbelt Systems in the Hetao Irrigation Area, China

        LIU Liyuan, FENG Tianjiao, XIAO Huijie, JI Mingxin, LI Junran, WANG Dong

        DOI: 10.11766/trxb202406280264

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        Abstract:

        Farmland shelterbelt systems are crucial for improving soil moisture and carbon conditions, ensuring crop production, and enhancing the quality of the ecological environment. However, while serving as a barrier to agricultural ecosystems, farmland shelterbelts also compete with crops for nutrients and moisture resources, resulting in both positive and negative environmental effects. Therefore, exploring the factors influencing the spatiotemporal variations of moisture and carbon conditions within farmland shelterbelts with typical configuration is essential to effectively enhance the ecological benefits of farmland shelterbelt systems, scientifically constructing shelterbelt forests, and improving the ecological environment. In this study, we selected typical configurations of farmland shelterbelt systems, including two-row, four-row, five-row, and eight-row forest belts in the Hetao Irrigation Area. We measured the soil moisture storage (SMS) and soil carbon stocks (SCS) across various spatial positions at different horizontal distances from the shelterbelts (0.3H, 1H, 2H, 3H, 4H, where H represents the height of mature trees) and at different depths (0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm), as well as at different temporal scales (early, mid, and late growing seasons across various months). Additionally, the study examined ecological environmental factors, including soil properties, vegetation attributes, and microclimatic factors, to investigate the key factors influencing soil moisture storage and soil carbon stocks within farmland shelterbelt systems. The results showed that: (1) SMS and SCS were highest in the four-row forest belts, with 240.2 mm and 26.7 kg·m-2, respectively, and lowest in the two-row forest belts, with 195.4 mm and 16.1 kg·m-2, respectively. Overall, the general pattern of soil moisture storage and soil carbon stocks across different shelterbelt configurations was four-row > eight-row > five-row > two-row. (2) For the temporal scale, the highest mean SMS (277.7 mm) was recorded in May, while the highest mean SCS (22.04 kg·m-2) was recorded in October. Regarding the horizontal distance, SMS exhibited an increasing trend with distance from the shelterbelt, whereas SCS displayed a decreasing trend. In terms of vertical depth, SMS increased with depth, while SCS gradually decreased as depth increased. (3) Farmland shelterbelts significantly reduce wind speed, solar radiation, and air temperature while enhancing relative humidity and minimizing soil evaporation, with the four-row forest belts exhibiting optimal microclimatic regulation and overall benefits. (4) The ranking of ecological environmental factors affecting soil moisture storage and soil carbon stocks was as follows: soil properties > microclimate factors > vegetation attributes. By analyzing and evaluating the effects of each environmental factor on SMS and SCS under different patterns of farmland shelterbelt systems, this study provides a theoretical basis and scientific foundation for constructing farmland shelterbelt ecosystems.

      • Deliberations on Collaborative Supervision of Risk Control and Remediation for Soil Pollution of Constructed Land

        CHANG Chunying, HUANG Zaoquan, LÜ Mingchao, LI Zhaohui, DENG Yirong

        DOI: 10.11766/trxb202408280345

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        Abstract:

        Soil pollution risk control and remediation is the key to the safe use of constructed land. The effectiveness of this work is influenced by both technological development and environmental management, and the systematic and coherent linkage of supervision is crucial. National and local governments have made diverse attempts at the collaborative supervision of soil environments within constructed land. Utilizing local legislation, regulatory documents, and technical standards, these strategies have progressively honed and standardized the allocation of departmental responsibilities, process supervision, and access management, leading to effectively controlling the environmental risks of contaminated sites. Despite these advancements, there is a clear need for further bolstering the all-encompassing and interconnected nature of coordinated supervision. This thesis, based on the analysis of the natural attributes, socio-economic attributes, and soil remediation particularities of constructed land, systematically reviews the current status and typical issues of constructed land soil pollution risk control and remediation, and provides suggestions on optimization of collaborative supervision. Overall, within the framework of the national institutional system, local governments were focused on refining the scope of supervision, formulating implementation details, and strengthening supervision and implementation to meet national requirements, without imposing additional demands. In addition, the text analyzes issues such as unclear scope of joint supervision, insufficient planning considerations, shallow integration of land transfer, and inadequate integration of land plot information. It advances a suite of recommendations for enhancing the coordinated supervision framework, including clarifying supervisory scopes, alignment of land planning with soil remediation endeavors, specification of land transfer procedures, embracing a unified national land spatial "one map" strategy, and strengthening of oversight through a multiplicity of approaches. Future investigative trajectories may delve into the realms of precision regulation, pivot to green and low-carbon remediation methodologies, and digital transformation of soil pollution oversight, all aimed at significantly elevating the collective impact of coordinated supervision. This study offers valuable insights for enhancing the integrated regulatory framework for soil risk control and remediation on constructed land, thereby ensuring the safe and effective use of such land.

      • Study on the Composite Pollution of Degradable Microplastics and Thiacloprid

        TIAN Jiayu, GENG Dongmei

        DOI: 10.11766/trxb202409150367

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        【Objective】Microplastics (MPs) and neonicotinoid pesticides are widespread pollutants in agricultural soils, however, their interactions have not been fully studied. Thus, this study aims to explore the interactive mechanisms between biodegradable MPs [poly(butylene succinate), PBS] and neonicotinoid pesticide (thiacloprid, THI). 【Method】The interactive and adsorption mechanisms of THI on PBS were investigated through adsorption kinetics and isotherm models by considering the influence of common environmental factors like pH, salinity, and dissolved organic matter. Also, the desorption of pre-adsorbed THI from PBS using pure water and simulated intestinal fluid (SIF) as background solutions was evaluated. In addition, the bioavailability of THI in red and black soils treated with different proportions of PBS was compared and analyzed using thin film diffusion gradient (DGT) technology. 【Result】The results revealed that the adsorption process of THI on PBS was consistent with the pseudo-second-order kinetic model, indicating that chemical adsorption was predominant. Also, the adsorption isotherm analysis indicated that the adsorption of THI by PBS was multi-layered, and the experimental data fitted both the Henry and the Freundlich models well (R2 > 0.99). The results also showed that an increase in pH and salinity promoted the adsorption of THI while changing the concentration of dissolved organic matter had little effect on the adsorption process. Furthermore, the desorption experiments found that using SIF, the maximum amount of THI desorbed was 39.4 μg?g-1, which was 1.16 times higher than that desorbed by pure water, suggesting that THI is more easily desorbed in the SIF environment. Using the DGT technology, it was observed that the bioavailability of THI in soil increased after the addition of PBS, and the increase became more significant as the ratio of PBS added was increased. 【Conclusion】PBS can adsorb and desorb THI, and when added to soil, PBS can affect the bioavailability of THI. These findings provide important information for understanding the impact of MPs on the environmental behavior of neonicotinoid pesticides under actual environmental conditions and offer a new perspective on the environmental risk assessment and management of pesticides.

      • Toxicokinetics of Phenanthrene in Enchytraeus crypticus

        XIAO Naichuan, YOU Lelin, LIU Jiawen, DAI Wencai, ZHANG Tingting, GAO Ming

        DOI: 10.11766/trxb202409050359

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        【Objective】Enchytraeus crypticus is a model species widely used in toxicology studies and soil environmental risk assessments. It is known for its low sensitivity to polycyclic aromatic hydrocarbons (PAHs) which are prevalent soil contaminants. However, there remains a lack of toxicokinetic research on this species. This study selected phenanthrene as a representative PAH to investigate its toxicokinetics on E. crypticus under different exposure concentrations. 【Method】Laboratory experiments were conducted to study the toxicokinetics of phenanthrene on E. crypticus at three concentrations: 20, 40, and 80 mg?kg-1. Phenanthrene uptake and elimination were monitored over time. Toxicokinetic modeling was used to calculate the uptake rate constant, elimination rate constant, and bioaccumulation factor (BAF). A comprehensive model was also fitted to assess the overall phenanthrene dynamics. 【Result】The results indicated that phenanthrene rapidly accumulated in E. crypticus during the initial exposure phase and reached steady-state concentrations of 47.83±11.69, 106.8±15.52, and 364.1±51.11 mg?kg-1 at exposure levels of 20, 40, and 80 mg?kg-1, respectively. During the elimination phase, phenanthrene was eliminated at a decreasing rate over time. The uptake rate constants increased significantly with exposure concentration, while the elimination rate constants declined, resulting in elevated BAF values at higher concentrations. E. crypticus exhibited high tolerance and bioaccumulation potential for phenanthrene, with prolonged retention at high exposure levels, posing potential risks to soil ecosystems. 【Conclusion】The study concludes that the concentration-dependent toxicokinetics of phenanthrene, particularly differences in uptake, accumulation, and elimination, could result in varied soil environmental risk assessments. These findings underscore the need for careful consideration of such concentration-dependent dynamics in PAH risk evaluations. Furthermore, low-sensitivity species like E. crypticus should receive special attention in environmental risk assessments to ensure accurate evaluations of PAH-related risks.

      • Changes in plant- and microbial-derived soil organic carbon in three temperate mature forests

        Liuxinying, Taoyulan, Wangyanping, Zhaoxuechao, Yang shanwu, Wang shandi, Huang li, Li wenhui, Qingkui Wang

        DOI: 10.11766/trxb202406130233

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        Abstract:

        【Objective】Forest ecosystems are the largest carbon pool in terrestrial ecosystems, and forest soils are the largest organic carbon pool in terrestrial ecosystems. Soil organic carbon (SOC) is an important component of the carbon pool in terrestrial ecosystems, and plant- and microbial-derived organic carbon are the key components of SOC. So, an advanced understanding of the effects of forest types on plant- and microbial-derived organic carbon is important. 【Methods】From three types of temperate forests: Pinus densiflora, Robinia pseudoacacia and Quercus acutissima, 0-10 cm mineral soil was collected to analyze the contents of lignin phenols and amino sugars, which are biomarkers of soil organic carbon of plant- and microbial-derived organic carbon. Also, the basic physical and chemical properties of soil, and the community structure and activity of microorganisms were investigated. 【Result】The soil total amino sugars, amino glucans, amino galactose, and cytosolic acids were significantly lower in P. densiflora than in R. pseudoacacia and Q. acutissima, Also, the bacterial, fungal, and microbial residue carbon was significantly lower in P. densiflora than in Q. acutissima and R. pseudoacacia, and the content of microbial residue carbon in R. pseudoacacia and Q. acutissima was 1.9 and 2.3 times higher than that in P. densiflora. The contribution of microbial residue carbon to SOC in R. pseudoacacia, Q. acutissima, and P. densiflora was 56.79%, 57.41%, and 52.55%, respectively. In addition, the content of fungal residue carbon was 12.76-16.56 times higher than that of bacterial residue carbon, and its contribution to organic carbon was much larger than that of bacterial residue carbon. Furthermore, it was observed that the content of total lignin phenol and its three types of monomers (V, S and C) followed R. pseudoacacia>Q. acutissima>P. densiflora with, the content of total lignin phenol in R. pseudoacacia and Q. acutissima being 3 and 2.8 times higher than that in P. densiflora. Also, the acid-aldehyde ratios of Vanillyl-based ((Ad/Al)v) and Syringyl-based ((Ad/Al)s) in the soil of R. pseudoacacia were significantly higher than those in Q. acutissima and P. densiflora, suggesting that the decomposition of soil lignin was higher in the R. pseudoacacia.Random forest model predictions showed that total nitrogen, organic carbon, total phosphorus, pH, and xylanase were the main factors affecting soil microbial, bacterial, fungal residue carbon and lignin phenols. Following the structural equation modeling, it was recorded that soil physicochemical and microbial properties are latent variables that have a strong influence on soil microbial residual carbon and lignin content,【Conclusion】Our results indicate that microbial growth can be promoted by improving soil nutrients and microbial properties. Eventually, increasing microbial and plant-derived organic carbon content and contribution to the SOC pool in temperate forest management can, maximize its carbon sequestration potential.

      • Response Characteristics and Influencing Factors of Soil Organic Carbon to Reduced Chemical Fertilizers or Organic Fertilizer Substitution

        Wu Nengxiang, Wang Ping, Liu Yalong, Wang Jingkuan

        DOI: 10.11766/trxb202408190332

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        Abstract:

        Delving into the impacts of reduced chemical fertilizers (RCF) and organic fertilizer substitution (OFS) on soil organic carbon (SOC) is crucial for understanding the response processes of agricultural SOC pools to fertilization and achieving sustainable agricultural development early. This study aims to explore the impacts of RCF and OFS on SOC under different climatic conditions, initial soil properties, and land use patterns. Furthermore, it endeavors to estimate the key influencing factors and clarify the natural and anthropogenic conditions conducive to SOC accumulation.【Method】After collecting and sorting out 142 published literature, we analyzed the variation characteristics of SOC content under RCF and OFS using meta-analysis. Thereafter, the influence degrees of various factors on SOC were systematically investigated by the Random Forest Model.【Result】The results revealed that SOC decreased by 2.61% on average under RCF. Notably, greater SOC losses were observed in temperate regions (with annual mean temperature < 10°C and annual mean precipitation < 1000 mm), whereas SOC losses were not significant with changes in altitude. Soils with high initial SOC content favored SOC retention. With soil’s initial pH and available phosphorus content increasing, the overall loss of SOC tended to intensify, with the highest SOC reduction reaching 6.91%, however, the effect of initial available potassium was the opposite. The declines in SOC under RCF were similar in farmland and orchards, while changes in SOC in vegetable fields were not significant. In contrast, SOC significantly increased by 14.39% under OFS, with subtropical regions at low to medium altitudes and annual precipitation < 600 mm being more conducive to SOC accumulation. Except for low levels of initially available nitrogen (50 mg·kg-1), no significant differences in SOC were observed among soils with different initial SOC, total nitrogen, and available nitrogen contents. With initial pH and available phosphorus content increasing, the cumulative effect of SOC enhanced, whereas the effect of initially available potassium was the opposite. Among different land use types under OFS, paddy-upland rotation and vegetable field utilization were most favorable for SOC accumulation.【Conclusion】Under the two fertilization systems, the climatic and environmental conditions in subtropical regions are more conducive to SOC sequestration. Compared to the subsurface soil, the impact of RCF and OFS on SOC in the surface soil was more significant. The decline in SOC of RCF was similar in both farmland and orchards, while the change of SOC in vegetable fields was not significant. In contrast, paddy-upland rotation and vegetable fields were the most favorable practices for SOC accumulation under OFS. Additionally, pH and initially available nitrogen were the most critical factors influencing the changes in SOC with RCF and OFS, respectively. These research results are of great significance for achieving carbon neutrality and sustainable development in agriculture as soon as possible.

      • Differences in Soil Carbon Sequestration Effects of Long-term Carbonization Straw Return on Soil in Acidic Red Soil Areas in Southern China

        YANG Xin, XU Lingying, XIA Longlong, ZHAO Xu

        DOI: 10.11766/trxb202405210205

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        Abstract:

        【Objective】 Converting agricultural straw into biochar and then returning it to the field has received widespread attention at domestic and abroad as a potential pathway for soil improvement and carbon sequestration and emission reduction in the southern acidic red soil area. 【Method】 Relying on the soil column experiments of rice-wheat (paddy-upland）rotation and millet-wheat (upland-upland) rotation established in June 2011, the organic carbon accumulation characteristics and changes in the organic carbon functional group structure of paddy soils (QP and TP) and upland soils (QU and TU) developed from Quaternary red clay and Tertiary red sandstone soils were observed under long-term straw biochar application (BC0, 0 t·ha-1 per season; BC11.3, 11.3 t·ha-1 per season). The relationship between soil organic carbon quantity, structure, stability indicators and soil properties was analyzed, in order to clarify the differences in carbon sequestration effect of biochar application on different acid red soils. 【Result】 The results showed that soil texture, land use type and their interaction significantly affected soil organic carbon density under biochar treatment. Compared with BC0, the increase in soil organic carbon density from 0-20cm was higher in partial clayey soils (QP, 25.22 kg·m-2; QU, 8.07 kg·m-2 ) than sandy soils (TP, 8.67 kg·m-2; TU, 7.58 kg·m-2 ), and higher in paddy soils (QP, TP) than upland soils (QU, TU) after 11 years of BC11.3 treatment. The results of 13C solid-state NMR showed that under the same farming conditions, there was no significant difference in the composition of organic carbon functional groups and stability indicators of soil with different textures. The ratio of alkyl carbon and o-alkyl carbon in paddy soil is higher than that in dryland soil, and the ratio of aromatic carbon, hydrophobicity index and aromaticity are lower than that in dryland soil. pH, bulk density, field water capacity, and total porosity all significantly affected the soil organic carbon content and its stability indicators after biochar application. 【Conclusion】 The above results show that the organic carbon sequestration of partial clay soil is higher than that of sandy soil after long-term straw carbonization and returning to the field in the sour red soil area of South China, but there is no difference in long-term stability. The sequestration of organic carbon in paddy field is larger than that in upland, but upland is more conducive to the long-term stability of soil organic carbon. In this study, we investigated the mechanism of carbon sequestration effect difference between different soils from soil organic carbon and its structural characteristics, and provided scientific basis for the rational use of straw biochar resources.

      • Reduction Effect of Reductive Soil Disinfestation on Soil Biological Co-contamination in Different Farmland Soils

        YU Wenhao, YANG Zhiyi, ZHANG Jingqing, LIU Liangliang, HUANG Xinqi, ZHANG Jinbo, CAI Zucong, ZHAO Jun

        DOI: 10.11766/trxb202405290213

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        Abstract:

        [Objective] In recent years, the enrichment of soil-borne pathogens and antibiotic resistance genes (ARGs) has led to biological co-contamination of soil, posing a serious threat to agricultural product safety and human health. [Method] To investigate the synergistic remediation effect of reductive soil disinfestation (RSD) on soil biological co-contamination, intensive farmland soils (black soil, red soil and fluvo-aquic soil) with co-contamination of Ralstonia solanacearum, ARGs, and mobile genetic elements (MGEs) were selected. RSD was applied with 1% ethanol (ET,), alfalfa meal (AL, C/N: 21.2), and molasses (MO, C/N: 12.6), alongside controls of maximum water holding treatment (FCK) and untreated soil (CK). Real-time PCR was used to analyze the changes of R. solanacearum, major ARGs and MGEs before and after treatment, and the reduction rate of relative abundance was used to measure the mitigation effect of RSD treatment on soil biological co-contamination. [Result] The results showed that RSD could effectively reduce a variety of ARGs and MGEs, among which AL and MO treatment could decrease the relative abundance of aadA7, aadA21, tet36, sul1, and IS6100 genes in black soil, with a reduction rate of 28.4%~49.9%. After ET treatment, the relative abundance of aadA7, msrE, tetG, tetM, tet36, intl1, IS6100, and IS26 genes in fluvo-aquic soil decreased significantly, and the reduction rate reached 56.2%~81.6%. Additionally, RSD efficiently reduced the relative abundance of R. solanacearum in soil, and the decrease in red soil and fluvo-aquic soil was 88.0%~92.3% and 76.1%~94.2%, respectively. Correlation analysis showed that there was a certain coupling relationship between the relative abundance of R. solanacearum and ARGs and MGEs. In fluvo-aquic soil, the relative abundance of R. solanacearum was significantly and positively correlated with the relative abundances of most ARGs (aadA7, msrE, tetG, tetM, and tet36) and MGEs (intl1, IS6100, and IS26) genes, indicating that RSD treatment had a good synergistic reduction effect on the biological co-contamination in fluvo-aquic soil. Furthermore, there were considerable differences in the correlation results between the relative abundance of R. solanacearum, ARGs, and MGEs and soil physicochemical properties in different soil types. This indicates that the effectiveness of RSD treatment in remedying soil biological co-contamination varies depending on soil physicochemical properties. [Conclusion] RSD can synergistically reduce soil biological co-contamination caused by the superposition of soil R. solanacearum, ARGs, and MGEs, but its reduction effect is affected by soil and organic material types.

      • Impacts of straw return on the community structure and functional activity of nitrogen-fixing microorganisms in paddy soil

        CHEN Pei, CHENG Yu, ZHAO Ying, WANG Ning, Li Shi-wei, XUE Li-hong

        DOI: 10.11766/trxb202406140054

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        【objective】Nitrogen-fixing bacteria are crucial for biological nitrogen fixation in paddy fields. Returning straw to these fields increases the soil carbon-to-nitrogen ratio (C/N), potentially impacting the diversity and functionality of nitrogen-fixing microorganisms. The rice rhizosphere, a highly active microbial zone, experiences rapid oxygen depletion from straw decomposition, which promotes anaerobic nitrogen fixation. Conversely, the growth of rice may release oxygen, thereby potentially inhibiting these microorganisms. Research on these intricate interactions within rice cultivation systems remains limited.【Methods】 In this study, the rhizosphere bag method was employed to explore the impact of varying straw return levels (0%, 1%, 2%) on the abundance and community structure of nitrogen-fixing bacteria, as well as on nitrogenase activity in the rhizosphere and bulk soil of two distinct paddy soil types (high sandy soil and yellow mud soil).【Result】The results indicated that, compared to no straw return, a 2% straw return significantly increased the abundance of nifH genes in the bulk of high sandy soil by approximately 86.2%, and in the rhizosphere of both soil types by 154% to 179%. In both types of paddy fields, the abundance of nifH genes in the rhizosphere soil was higher than in the bulk soil, particularly under the 2% straw return condition, with increases ranging from 68.3% to 101%. Principal Coordinates Analysis (PCoA) revealed significant changes in the composition of nitrogen-fixing microorganisms in the bulk soil of both soil types compared to their respective rhizospheres. Additionally, the community compositions of nitrogen-fixing bacteria in the rhizosphere were distinctly separated from those in the bulk soil. The response of soil nitrogenase activities to straw return was inconsistent with that of nitrogen-fixing bacteria. Under a 1% straw return, nitrogenase activity in the bulk of high sandy soil showed no significant change, but increased by nearly 33.8% with a 2% return. Conversely, nitrogenase activity in the rhizosphere of high sandy soil decreased significantly by 18.3% to 37.2% under both straw return conditions. In contrast, in yellow mud soil, nitrogenase activity in both the rhizosphere and bulk soil significantly increased by 8.69% to 20.4% under a 1% straw return, but decreased under a 2% return.【Conclusion】In summary, the rhizosphere enhances the abundance of soil nitrogen-fixing bacteria and their enzyme activities by optimizing the soil environment. Meanwhile, straw return primarily increases soil organic carbon and the carbon-to-nitrogen (C/N) ratio, thereby boosting the abundance of nitrogen-fixing bacteria and altering microbial community diversity. The response of soil nitrogenase activity to straw return varies depending on the soil type and the amount of straw returned.

      • Response of soil protist communities to long-term grazing in desert steppe

        Yue Mei, De Hai Shan, Ye He, Zhao Yu, Shang Xing Ling, Li Shuo, Huang Kai chun, Hong Mei

        DOI: 10.11766/trxb202403070095

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        【Objective】Grazing is one of the most important, simplest, and most economical ways of grassland utilization in the Inner Mongolia desert steppe. It is an important factor affecting plant, biological, and soil environmental changes. Soil protists play an important role in the material cycle and energy flow of desert steppe ecosystems, but little is known about how the protists respond to changes in grazing intensity. 【Method】A randomized block experiment was conducted in a Stipa breviflora desert steppe to analyze the diversity and composition of soil protist communities. Four treatments were set up: CK (Control), LG (Light grazing), MG (Moderate grazing), and HG (Heavy grazing). High-throughput sequencing technology was used to analyze the diversity and composition of soil protist communities. Combined with the analysis of vegetation characteristics and soil physical and chemical properties, the key environmental factors driving the change of soil’s protist biological community were explored. 【Results】The results showed that the soil protist communities in the Stipa breviflora desert steppe were mainly composed of Unclassified-Eukaryotes, Cryptophyta, Chlorophyta, Arthropoda, Streptophyta and Mucoromycota. The dominant groups (relative abundance accounted for 20% or more of the total abundance) were Unclassified-Eukaryotes and Cryptophyta. The common groups (relative abundance accounted for 2%-20% of the total abundance) were Chlorophyta, Arthropoda, Streptophyta, and Mucoromycota. The rare groups (relative abundance accounted for 2% or less of the total abundance) were Chytridiomycota, Apicomplexa, Chordata, and Basidiomycetes. Among these, the dominant groups and common groups were more sensitive to the change in grazing intensity. Grazing intensity changed the vegetation characteristics, soil physical and chemical properties, and soil protist community diversity of desert steppe. The Margalef richness index, Shannon-Wiener diversity index, Pielou evenness index, and biomass of vegetation were sensitive to the changes in protist communities. The total porosity, bulk density, organic matter, total nitrogen, total phosphorus, available phosphorus, available potassium, and pH were the key soil factors affecting the protist community. 【Conclusion】In conclusion, grazing affects soil protist communities by changing vegetation characteristics and soil environmental factors. Our results prove that there is a strong connectivity between protist and environmental factors in ecosystems with relatively scarce nutrient resources and clarify the protist groups that are sensitive to changes in grazing management measures in desert steppe.

      • Temporal dynamics and fraction accumulation characteristics of black soil organic carbon under long-term continuous straw return

        Zhang Jiaqi, wangcui, Wang Mingming, Pan Fengjuan, Hao Xiangxiang, Sui Yueyu

        DOI: 10.11766/trxb202404290176

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        【Objective】Straw returning is an effective measure to increase the amount of soil organic carbon (SOC) in agroecosystems. The objective of this study was to study the temporal dynamic of SOC in Mollisols during long-term straw return. 【Method】Based on an 18-year long-term field experiment using a maize-soybean rotation cropping system in the typical black soil region，the temporal dynamic of topsoil (0-20 cm) organic carbon was studied under three treatments: no fertilizer (NF), mineral fertilizer (NPK), and mineral fertilizer with straw return (NPKS). Furthermore, physical and chemical fraction methods were applied to study the effect of straw return on SOC pools. 【Result】The results showed that: (1) Compared with the initial (2004) soil, the SOC content significantly increased by 12.97% in the NPKS treatment, with an annual increase of 0.18 g·kg-1, and the SOC content significantly decreased by 3.9% in the NF treatment, while no significant change was found in NPK treatment. (2) There was a significant positive correlation between SOC content and year and the cumulative carbon input in the NPKS treatment. In particular, a significant relationship between SOC and cumulative carbon was observed from 2004 to 2015 under NPKS, while not from 2015 to 2022, indicating that the increase of SOC caused by straw return mainly occurred in the first 11 years, and after 11 years, the SOC reached a state of equilibrium. (3) The NPKS treatment increased the carbon content in free light fraction (fLFC), occluded light fraction (oLFC), the heavy fraction (HFC), humic acid (HAC), fulvic acid (FAC), and humin (HMC) by 47.77%, 34.77%, 11.18%, 13.00%, 6.32%, and 11.71%, respectively. Straw return improved the C proportion in labile fractions (fLFC and oLFC) and decreased the proportion of HFC, but the contribution of HFC to SOC improvement was more than 80%. Thus, the stable HFC was a key component for the long-term sequestration of SOC. In addition, straw return increased the ratio of HA/FA, consequently, increasing the humification degree of soil organic matter. 【Conclusion】Long-term continuous straw return can effectively improve the content of SOC and its fractions in black soil, but after 11 years of continuous straw return, SOC will stop growing and reach a new equilibrium. Although the labile SOC was elevated at a higher percentage than the stable SOC，the stable SOC still plays a crucial role in maintaining the stability and quantity of SOC.

      • Differences in Soil Erosion Resistance Between Different Vegetation Types of Purple Soil in the Three Gorges Reservoir Area

        FENG T, CHEN Xiaoyan, ZHU Pingzong, PAN Zhenhua, YANG Lan, WANG Dingbin

        DOI: 10.11766/trxb202407080276

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        Abstract:

        【Objective】Soil erosion resistance reflects the vulnerability or sensitivity of soil to erosion, which is a critical parameter utilized for soil erosion prediction and is of significant importance for predicting regional soil erosion and adjusting land use patterns. Nevertheless, the potential effect as well as their driving mechanism of vegetation types on soil erosion resistance is still scarce in the purple soil of the Three Gorges Reservoir Area. Therefore, this study aimed to explore the potential effect of vegetation types on soil erosion resistance and decipher the influencing mechanisms of purple soil in the Three Gorges Reservoir area. 【Method】Based on a full field investigation in the Qinling watershed of Zhongxian Country in the Three Gorges Reservoir area, seven typical vegetation types of the coniferous forest of Cupressus funebris Endl. (CF) and Pinus massoniana Lamb. (PM), broadleaf forest of Eucalyptus spp. (E), Citrus reticulata Blanco.(CR), shrub (S), grassland (G) and maize (M) were selected. Combined with the field sampling and indoor analysis, difference analysis, correlation analysis, redundancy analysis and path analysis, the differences as well as the main influencing factors of soil erosion resistance between different vegetation types were comprehensively analyzed. 【Result】The comprehensive soil erosion resistance index (CSRI) varied from 0.05 to 0.72 between different vegetation types, among which maize had the minimum CSRI, then followed by CR, G, E, PM, S and CF. Moreover, CSRI varied significantly between different vegetation types with the CSRI of SL and CR being significantly lower than that of other vegetation types. Compared to M, CSRI of CR, G, E, PM, S, and CF increased by 210%, 407%, 779%, 816%, 1095% and 1217%, respectively. Differences in CSRI between different vegetation types was closely related to near-surface soil properties and vegetation characteristics. Correlation analysis indicated that CSRI was significantly positively correlated with organic matter content, water-stable aggregates content, total porosity, clay content, litter weight of the semi-decomposed layer, and root mass density, whereas significantly negatively correlated with bulk density (p<0.05). The results of redundancy analysis showed that water-stable aggregates, clay, and organic matter contents were the main factors controlling the differences in CSRI between different vegetation types, which could explain 64% of the total differences. However, the influencing mechanism of vegetation types on CSRI in purple soil was different from most previous studies carried out in other regions. Influenced by the formation process of purple soil, variation in CSRI between different vegetation types was dominantly controlled by clay content via its direct effect and indirect effect through increasing organic matter and water-stable aggregates contents. 【Conclusion】Sloping land and orchard land are still the potential areas of soil erosion in the Three Georges Reservoir area since it has the minimum CSRI. Cupressus funebris Endl land can be promoted as soil and water conservation species in the reservoir area. The relevant research results can provide a scientific basis for the adjustment of land use structure and the selection of tree species for soil and water conservation, to realize the green and sustainable development of the Three Georges Reservoir area.

      • Regional Differences of Farmland Soil Organic Carbon Pool Changes in Fujian Province from 1982 to 2018

        LONG Jun, ZHANG Liming, HUANG Qian, ZHANG Xiu, BIAN Ana, ZHU Lixia, CHEN Qingsen, XING Shihe

        DOI: 10.11766/trxb202409220371

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        Abstract:

        【Objective】Estimating the spatial-temporal changes of farmland soil organic carbon density (SOCD) provides a scientific basis for food security and double-carbon strategy.【Method】In this study, a total of 371,976 polygonal patches and 57,254 sampling sites were used to establish 1:10,000 databases. The raster dataset of soil organic matter content was interpolated using the simple kriging method combining with ancillary variables of terrain information, which was an optimal interpolation established in the earlier study based on the idea of “ideal interpolation method + efficient auxiliary variables”. Then, the SOM content was assigned to each polygonal patch of the farmland map with the help of the spatial analyst tools of ArcGIS v. 10.8 software. Eventually, the SOCD was calculated. Moreover, the gravity center migration model was employed to quantify the regional differences in farmland SOCD changes in Fujian Province from 1982 to 2018. The regions mentioned above referred to different administrative regions of nine cities, soil types of nine soil groups, three land use types of paddy fields, dry-land, and irrigated land, and two climatic zones such as the middle subtropics and south subtropics of Fujian. Also, these nine cities were divided into the southeastern coastal cities and northwest inland cities of Fujian.【Result】The farmland soils in different regions had dual functions of carbon source and sink in the past 40 years. Viewed from the area ratio of farmland soil carbon source and sink, the carbon sequestration capacity or loss intensity of most farmland was concentrated in the range of 0～1 kg·m-2, regardless of administrative regions, soil types, land use types, or climatic zones. Specifically, the farmland SOCDs in the southeastern coastal cities of Fujian were 2.37～2.65 kg·m-2 and 2.23～2.83 kg·m-2 in 1982 and 2018, respectively, which were much lower than those of northwest inland cities (2.92～3.24 kg·m-2 and 2.99～3.30 kg·m-2). It was also found that Putian was the only city to experience a decline in SOCD, with a carbon source effect of 0.31 kg·m-2. In terms of soil types and land use patterns, paddy soils and paddy fields were the most important carbon sink, with SOCD increased by 0.10 kg·m-2, while coastal solonchaks, aeolian soils, and dry-land contributed as a carbon source, with SOCD decreased by 0.23 kg·m-2, 0.22 kg·m-2 and 0.03 kg·m-2, respectively. When it came to climatic zones, the farmland soil in the middle subtropics of Fujian increased from 3.02 kg·m-2 (1982) to 3.16 kg·m-2 (2018) in SOCD, with higher SOCD level and carbon sequestration efficiency than those of south subtropics.【Conclusion】The farmland soil organic carbon pool changes varied greatly with regions in Fujian Province from 1982 to 2018. These changes might have been mainly influenced by a combination of intrinsic soil factors and external factors such as human disturbance. Thus, our work suggests that in formulating policies for farmland carbon sequestration management in Fujian in the years to come, priority should be given to the SOCD level in different regions and their change differences.

      • Characteristics of Perched Water Recharge in the Dam Land of Yangjuangou Small Watershed on the Loess Plateau

        YU Lulu, JI Zhenxia, WANG Li

        DOI: 10.11766/trxb202406240256

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        【Objective】Check dams, as one of the core projects for soil erosion control in the Loess Plateau region, have played an irreplaceable role in preventing soil erosion and improving the ecological environment. By intercepting runoff and depositing sediment, check dams effectively reduced soil erosion, which in turn improved the local ecological environment and agricultural production conditions. However, despite the remarkable success of check dams in soil and water conservation, research on the perched water in dam lands on the Loess Plateau remains insufficient, particularly in understanding the recharge process and mechanisms of the perched water. The study is of great significance for the comprehensive understanding of the ecological function and hydrological role of check dams.【Method】Based on this, dam lands were selected in typical watersheds of the Loess Plateau as the research object, and using iodide and bromide ions as tracers, along with water level monitoring and chlorine mass balance method, the recharge process of perched water in the dam land was systematically traced. The core objective of the study was to reveal the recharge process and mechanism of perched water in dam land under different land use types, and to provide a scientific basis for water resource management.【Result】The results showed that soil moisture in the dam land under different land use types followed the order: farmland > shrubland > arbor land > grassland. Different land use types had a significant impact on the recharge rate of perched water in the dam land. Specifically, the recharge rate of farmland was the highest, followed by arbor land, then grassland, with shrubland having the lowest recharge rate, ranging from 32.94 to 60.96 mm·a-1. This difference reflects the influence of different vegetation types and land management practices on the perched water recharge process, providing important clues for understanding the hydrological functions of different ecosystems. Furthermore, it found that when the precipitation exceeded 15 mm·d-1, water could infiltrate into the perched water and quickly recharged it. At this time, the vertical infiltration rate of water was about 0.13 to 0.15 m·d-1. However, this recharge process was not immediately completed as there was a lag time of about 6 to 11 days, suggesting that the recharge of perched water has a time-lag effect. In addition, the results of iodine ion tracer experiments showed that the perched water in the dam land had good connectivity, with a horizontal water transport rate of 6 m·d-1. This finding suggests that the perched water has a strong hydraulic connection, which could realize the horizontal distribution and redistribution of water within a certain range, and thus form a relatively stable hydrological cycle system on a local scale.【Conclusion】Overall, this study not only reveals the recharge process and mechanism of perched water in the dam land, but also provides an important theoretical reference and scientific basis for further understanding of the perched water in the dam land. Through these research results, the water resource dynamics of the dam land can be better grasped, and technical support can be provided for soil and water conservation and ecological restoration in the Loess Plateau region. These studies can provide strategies to optimize the management and maintenance of check dams, and further promote the protection and improvement of the regional ecological environment.

      • Spectral Characteristics of Dissolved Organic Matter in Soils with Diverse Vegetation Cover in the River-Lake Confluence Area of Hongze Lake

        CHENG Hu, WU Yudong, GUO Yanhui, MIN Ju, LU Haiying, HAN Jiangang, ZHANG Longjiang, JI Rongting

        DOI: 10.11766/trxb202408070322

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        Abstract:

        【Objective】Soil dissolved organic matter (DOM) plays an important role in the biogeochemical processes in wetland ecosystems. This study aimed to uncover the total quantity, components, and source features of DOM in the river-lake confluence area of Hongze Lake. 【Method】The spectral characteristics of DOM in soil covered by lake-sedge, reed, poplar, and willow in the river-lake confluence area of Hongze Lake were studied using UV-visible absorption spectroscopy and the three-dimensional fluorescence spectroscopy method. 【Result】The results showed that the DOM content of soil covered by different vegetation was in the order of reed wetlands, lake-sedge wetlands, poplar forests, and willow forests. Additionally, soil within 40 cm of reed wetlands contained a dissolved organic carbon level of 193.2 mg·kg–1. The soil DOM values of A250/A365, SUVA254, SUVA260, and SR ranged from 3.7 to 4.5, 1.3 to 1.8, 0.86 to 1.8, and 3.6 to 4.9, respectively. Moreover, the molecular weight, aromaticity, and hydrophobicity of lake-sedge wetlands soil were significantly higher than those of other soils. As revealed, DOM""s molecular weight, aromaticity, and hydrophobicity decreased in the 20~40 cm soil layer as opposed to the 0~20 cm soil layer. As shown by EEM-PARAFAC, four fluorescence components, terrestrial humic acid-like, marine humic acid-like, fulvic acid-like, and protein-like, have been recognized. Humic acid-like substances were found in all soil layers, with 55.1% to 70.1% being the majority, but the 20~40 cm soil layer saw a rise in protein-like substances, especially in reed wetlands soil. The FI, BIX, and HIX indices of DOM varied depending on the vegetation, with a range of 1.3 to 1.5, 0.47 to 0.72, and 1.7 to 7.4, respectively. The soil DOM properties were greatly influenced by the coverage of different vegetation. Also, terrestrial humic acid-like substances were the dominant soil DOM in the river-lake confluence area of Hongze Lake, with a lesser level of self-obtained and a higher degree of humification. 【Conclusion】In summary, the research results revealed the differences in total DOM content and spectral characteristics of soils with different vegetation cover in the river-lake confluence area of Hongze Lake. It further provides a scientific basis for understanding DOM environmental behavior in the river-lake confluence area, thus, strengthening carbon sequestration efficiency in key areas and enhancing habitat protection.

      • Effects of Sustained Low Level Organic Fertiliser and Chemical Fertiliser Blending on Soil Fertility and Multifunctionality inOasis Farmland

        WANG Bing, ZHANG Yuchen, WANG Xinyue, WU Maolin, PENG Yi, HUANG Wei, FENG Gu, YAN Qiwen, JIANG Ping’an, LIU Yunhua, SHENG Jiandong

        DOI: 10.11766/trxb202404130153

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        Abstract:

        【Objective】The usage of organic fertilizers in arid zones is limited, which necessitates investigating the most suitable amount required for optimum agricultural productivity, and clarifying the degree of influence on soil physicochemical properties, microbial communities, and multifunctionality in oasis farmland when applied in low amounts in combination with chemical fertilizers.【Method】A field experiment was conducted in Hailou Town, Shaya County, Xinjiang from 2021 to 2023. High-throughput sequencing (16S rRNA and endogenous transcribed spacer region) technology was used to determine and analyze the extent of the effects of organic fertilizer application on soil nutrient physicochemical properties, microbial community composition, and diversity, and to explore the response of soil multifunctionality to organic fertilizer dosage. Four treatments were set up: NPK (chemical fertilizer only), NPK + OM3 (3 000 kg?hm-2 cattle manure + chemical fertilizer), NPK + OM6 (6 000 kg?hm-2 cattle manure + chemical fertilizer), and NPK + OM12 (12 000 kg?hm-2 cattle manure + chemical fertilizer).【Result】The results showed that: (1) Application of organic manure significantly increased soil organic carbon, total nitrogen, available phosphorus, available potassium and nitrate nitrogen, and significantly decreased soil pH; (2) NPK + OM6 and NPK + OM12 treatments significantly increased microbial (Chao1 and Shannon index) and fungal (Shannon index) diversities, and significantly changed the community structure; (3) The relative abundance of Blastomonas, Acidobacilli and Glomus increased, but that of Actinomycetes and Campylobacter decreased with the increase in manure application rate; (4) The application of organic fertilizer can change the composition and diversity of bacterial community by changing soil nutrients and pH, thereby improving soil versatility.【Conclusion】Soil nutrients and microbial community composition and diversity increased significantly with the increase of organic manure application. Three years of organic manure application (3 000-6 000 kg?hm-2) could maintain soil multifunctionality at a high level by increasing soil nutrient content and improving microbial community composition and diversity. Considering the limited amount of organic fertilizer and the cost of fertilization, the application of 3 000-6 000 kg?hm-2 organic fertilizer in crop production in oasis farmland can achieve the effect of improving the multi-function of soil.

      • Latitudinal Zonal Variation of Surface Properties of Soil Particles with Different Particle Diameters

        YU Linqiao, HE Aizhou, LI Hang

        DOI: 10.11766/trxb202406210248

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        Abstract:

        【Objective】The spatial distribution of soil is consistent with the changes in bioclimatic conditions, with the soil mineral and organic composition also showing certain zonal changes. Consequently, the evolution of soil minerals accompanies the changes in soil surface properties. However, it remains unclear how these changes will vary among soil particles of different sizes. The goal of this study was to research the surface properties of soil particles with different diameters of 0-500, 500-1 000, 1 000-2 000, and > 2 000 nm in the latitudinal zonal soils and reveal the zonal changes of soil particle surface properties in different particle diameter ranges. 【Method】The surface electrochemical properties (specific surface area, surface charge amount, charge density) of soil particles were determined by the combined determination method, the organic matter of soil particles was determined by the potassium dichromate method, the mineral composition of soil particles was determined by X-ray diffractometer. 【Result】It was found that: (1) < 2 000 nm soil particles played a major role in the contribution of soil organic matter, secondary minerals, specific surface area, and surface charge while < 500 nm soil particles were the largest contributors to the soil specific surface area and surface charge. (2) With the decrease of latitude, the content of 0-500 nm particles gradually increased, the content of secondary minerals increased, the content of organic matter decreased, and the soil surface charge and specific surface area showed decreasing trends. (3) The soil-specific surface area and surface charge in the high latitude area increased linearly with the increase of the content of organic matter and montmorillonite, and the influence of montmorillonite content was greater than that of organic matter content. There was no obvious linear relationship between the specific surface area and surface charge with the increase of illite content. Also, the soil-specific surface area and surface charge increased linearly with the increase of organic matter content in the low latitude area while there was no obvious linear relationship between the specific surface area and surface charge with the increase of illite or kaolinite content. 【Conclusion】The soil specific surface area and surface charge at high latitudes were mainly affected by the contents of montmorillonite and organic matter, while the soil specific surface area and surface charge at low latitudes were mainly affected by the content of illite and organic matter.

      • Impact of Ralstonia solanacearum Invasion on the Interaction Between Bacterial and Fungal Communities in Tomato Rhizosphere

        PENG Junwei, LIU Qin, DONG Yuanhua, LI Jiangang

        DOI: 10.11766/trxb202408290347

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        Abstract:

        【Objective】Ralstonia solanacearum, a highly virulent plant pathogenic bacterium, causes bacterial wilt in tomatoes and other crops. This causes host death and significant yield losses, posing a serious threat to agricultural economies. The rhizosphere, as a critical environment for plant-microbe interactions, plays a decisive role in determining the outcome of pathogen invasion and plant health. However, the interactions between bacteria and fungi in the rhizosphere under pathogen invasion remain unclear, thus, limiting the understanding of the microbial changes associated with bacterial wilt disease.【Method】This study investigated the impact of R. solanacearum invasion on the composition and interaction networks of bacterial and fungal communities in the rhizosphere of diseased and healthy tomato plants. Quantitative real-time PCR (qPCR) was employed to quantify microbial abundances, while high-throughput amplicon sequencing was used to characterize the diversity and structure of bacterial and fungal communities. By comparing the microbial co-occurrence network in rhizosphere soils of diseased and healthy tomato plants, the study aimed to elucidate how pathogen invasion affects the microbial community structure and their ecological interactions.【Result】The results showed significant differences in the bacterial communities between the rhizospheres of diseased and healthy plants. The rhizosphere of diseased plants was invaded by a higher abundance of R. solanacearum, while the rhizosphere of healthy plants was significantly enriched with bacteria from the phyla Actinobacteria and Firmicutes, which include a greater number of beneficial bacteria with potential for biological control. Moreover, pathogen invasion reduced the ecological niche breadth and qPCR counts of fungi in the rhizosphere. Co-occurrence network analysis revealed that the bacterial-fungal network in diseased rhizospheres was more complex, with a significantly higher proportion of fungal nodes (46.7% compared to 31.0% in healthy rhizospheres). Among them, Ascomycota species emerged as key network nodes, indicating that pathogen invasion enhanced the close associations between bacteria and fungi (particularly Ascomycota species). In the direct bacterial-fungal interactions, the proportion of negative correlations in diseased rhizospheres (46.3%) was notably higher than in healthy rhizospheres (35.4%), suggesting that pathogen-induced interactions were predominantly antagonistic. Additionally, in the bacteria-fungi networks, Ascomycota and Actinobacteria were identified as key fungal and bacterial taxa, serving as biological indicators in diseased and healthy rhizospheres, with significant positive (R2 = 0.393, P = 0.002) and negative (R2 = 0.523, P = 0.000 2) correlations with pathogen abundance, respectively.【Conclusion】These results elucidate the disruptive effects of R. solanacearum on rhizosphere microbial communities, particularly the bacterial-fungal ecological interactions, and highlight the changes in rhizosphere microbial structures under bacterial wilt. This study provides a theoretical foundation for developing future strategies to control bacterial wilt in tomatoes.

      • Comparison of Digital Soil Mapping Methods in Plain and Hill Mixed Regions

        MENG Ke, HUANG Wei, FU Peihong, LI Wenyue, FENG Ling

        DOI: 10.11766/trxb202406210251

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        Abstract:

        【Objective】Digital soil mapping is a burgeoning and efficient method to express the spatial distribution of soil. Based on a data mining algorithm, this method establishes a soil-landscape relationship model to infer soil mapping by using raster data as an expression and computer-assisted. The key to improving the accuracy of digital soil mapping is constructing a suitable soil-landscape relationship model. However, the commonly used methods of digital soil mapping cannot meet the application requirements of soil mapping given the complicated nature of terrains consisting of plains and hills. How to fully consider the main links of the soil-landscape relationship model to accurately infer the spatial distribution of soil types needs further discussion. 【Method】The northern part of Chengmagang town, Macheng City, Hubei province was selected as the study area. It was divided into two terrain units, plains and hills. Based on the 28 environmental variables, Decision Tree (DT), Random Forest (RF), Gradient Boosting Decision Tree (GBDT), and Extreme Gradient Boosting (XGBoost) were used to select optimal mapping methods for each region. Then, the optimal variables combination was selected according to the factor importance ranking of each region. Moreover, the optimal mapping methods were used to establish a soil-landscape relationship model linking soil types to the optimal variable combinations, upon which soil type mapping was inferred for each region. Soil-type mapping results for plain and hilly areas were combined as the soil-type mapping result of the terrain region. Finally, the mapping accuracy of the whole region was compared with the terrain region to further explore ways to improve the accuracy of soil-type mapping in Plain and Hill Mixed Regions. 【Result】Under different terrain conditions, the performance of each inference mapping method was different as well as the optimal inference mapping method. The performance of RF and XGBoost was superior to other algorithms. Specifically, the RF performed better in whole and plain regions while the XGBoost was the best algorithm in the hill region. The model accuracy was further effectively improved through variable screening, with the maximum increase of overall accuracy and Kappa coefficient being 4.96% and 0.059 in the whole region, respectively. However, the model accuracy improvement was not obvious in the plain region, with the increase of overall accuracy and Kappa coefficient being 1.43% and 0.018, respectively. Also, the increase in overall accuracy and Kappa coefficient was 2.82% and 0.03 in the hill region. Compared with the whole mapping method, the inference mapping method based on terrain zoning had the highest accuracy, and the overall accuracy and Kappa coefficient were 73.05% and 0.69, respectively. Meanwhile, the plain region required more remote sensing factors to participate in inference mapping compared to the whole and hill regions. 【Conclusion】The inference mapping accuracy in plain and hill regions can be effectively improved by optimizing the mapping method, selecting environment variables, and adopting appropriate mapping way. This study can provide some references for the screening of environmental variables, the selection of mapping algorithms, and the construction of mapping ways of inference mapping in plain and hill regions. It provides promising and practical examples and technical support effective for promoting the improvement of the accuracy of inference mapping in complex terrain areas.

      • Change of Rill Erosion Microtopography on Saturated Loess Slope and its Response to Hydraulic Parameters

        TAN Qingfang, CHEN Fengting, HUANG Yuhan, ZHAO Mingquan, CHANG Zhiyong, WU Di, YU Xinxiao, HUAGN Zixuan, WEI Juan

        DOI: 10.11766/trxb202405210206

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        Abstract:

        【Objective】This study aimed to investigate the relationship between the hydraulic characteristic parameters of rill erosion and the changes in microtopography of the eroded, which is an important mechanism for investigating rill erosion.【Method】In this study, the loess was selected as the research material, and four slopes gradients(5°, 10°, 15°, 20°) and four flow rates (2, 4, 8, 16 L·min-1) were set. The limited rills with a width of 0.1 m were used to simulate the rill erosion experiment, combined with Structure-from-Motion (SfM) photogrammetry, the relationship between the hydraulic characteristic parameters of rill erosion on slopes and microtopographic variation were analyzed.【Result】The results showed that under the experimental conditions, the flow velocity ranged from 0.23 to 0.92 m·s-1 and slope had a greater influence on flow velocity than the flow rate. The ranges for the Reynolds number and Froude number were from 255 to 2358 and 1.89 to 5.90, respectively. These hydraulic characteristic parameters increased with an increase in both slope and flow rate (P<0.05), while the resistance coefficient exhibited the opposite trend. Surface roughness, relief amplitude, and surface incision depth varied within the ranges of 0.33 to 2.35 cm, 0.47 to 4.35 cm, and 0.53 to 2.53 cm, respectively. The surface roughness, relief amplitude, and surface incision depth were positively correlated with flow velocity, Reynolds number, and Froude number, but negatively correlated with the resistance coefficient. Additionally, surface roughness, relief amplitude, and surface incision depth increased in linear and power function trends with increasing flow velocity and Reynolds number.【Conclusion】As the slope and flow rate increased, all hydraulic characteristic parameters and microtopography factors of the eroded, except for the resistance coefficient, showed a significant increasing trend, indicating that the microtopography was evolving towards conditions that favored erosion. The surface roughness, relief amplitude, and surface incision depth showed a significant positive correlation with changes in flow velocity and Reynolds number. Additionally, the responses of these three microtopographic factors to changes in flow velocity and Reynolds number followed linear and power function relationships. When the flow was low, the variation in surface roughness was the greatest. As the flow rate increased, both the surface relief and the surface incision depth gradually increased, indicating that the downcutting effect of runoff during the erosion process was intense, leading to a continuous increase in rill erosion depth. Our research results can provide a theoretical basis for the control of soil and water loss in loess slope cultivated land and the study of regional ecological restoration.

      • Construction of Pedotransfer Function for Predicting Soil Bulk Density in Cultivated Land of Northeast China Using Random Forest

        WANG Xiaopan, WANG Changkun, SUN Haijun, GUO Zhiying, LIU Jie, GAO Lei, MA Haiyi, YUAN Ziran, YAO Chengshuo, PAN Xianzhang

        DOI: 10.11766/trxb202406180242

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        Abstract:

        【Objective】Soil bulk density (BD) is crucial for understanding the physical condition of black soil in cultivated land of Northeast China and advancing its utilization and protection. The traditional cutting ring method for determining BD is time-consuming and laborious, making the evaluation of BD on a large spatial scale difficult. The pedo-transfer function (PTF) can estimate BD information using readily available soil variables. However, there is currently a lack of research on PTF models specifically targeting the whole of Northeast China, and the importance of potential soil attribute variables for PTF model construction remains to be elucidated.【Method】By incorporating soil organic matter (SOM), moisture content (MC), and soil texture-related variables as input features, we constructed PTF models capable of predicting BD on a large scale. Furthermore, we delved into the significance of these soil attribute variables in the constructed PTF models. Additionally, we assessed the suitability of existing published PTF models for BD prediction in the black soil of Northeast China.【Result】The optimal predicted R2 values of published PTF were 0.17, 0.22, and 0.26, respectively, for the topsoil, subsoil, and all soil samples, and Root Mean Squared Errors ( RMSE) were 0.16, 0.13, and 0.15 g·cm-3, respectively. Also, the optimal predicted R2 values of PTF for the topsoil, subsoil, and all soil samples based on the proposed RF method were 0.22, 0.45, and 0.37, respectively, while the RMSE values were 0.16, 0.11, and 0.14 g·cm-3, respectively.【Conclusion】The published PTF models had low BD prediction accuracy and were difficult to use for BD prediction on the scale of black soil in Northeast China whereas the PTF model constructed in this study has the potential to predict BD on the scale of black soil in Northeast China. Among the variables, SOM was the most important variable for predicting BD in the black soil of Northeast China, followed by MC, while soil texture-related variables had a relatively small impact.

      • Evolution Characteristics of the Conversion Threshold of Different Potassium Forms in Two Typical Paddy Soils

        HU Congyue, HAN Guangzhong, YANG Jinling

        DOI: 10.11766/trxb202408060320

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        Abstract:

        【Objective】In the past few decades, soil potassium has received less attention than nitrogen and phosphorus, despite that potassium loss in farmland is a common issue due to large crop demand and the relatively small application amount. Soluble potassium resources are relatively unabundant in China. The low self-sufficiency rate and high reliance on imports led to the high cost of potassium fertilizers. Due to the importance of potassium in crop production and the cost and environmental consequences of applying potassium fertilizer, it is worth paying attention to mineral potassium in future agricultural production. It has been found that there is a unique potassium release mechanisms of layered silicate potassium-rich minerals in paddy soils. However, there is currently a lack of systematic research on the changes and influencing factors of different potassium transformation thresholds during the formation of paddy soils, which greatly limits the establishment and development of potassium transformation models for these soils. 【Method】This study selected "potassium-rich" purple paddy soil and "potassium-poor" red paddy soil, and investigated the evolution characteristics and influencing factors of different potassium transformation thresholds during their formation through time series analysis. The aim was to provide theoretical support for reducing the dependence on soluble potassium fertilizers in rice fields. 【Result】 For "potassium-rich" purple paddy soil, traditional rice cultivation in the early stages (within 0-20 years) significantly reduced the total amount of water-soluble potassium and exchangeable potassium in the plow layer (about a 28% decrease). After this period, the transformation thresholds between water-soluble potassium and exchangeable potassium, and between exchangeable potassium and non-exchangeable potassium, remained relatively stable, with thresholds stabilizing between 61±4 and 106±9 mg·kg-1, respectively. For "potassium-poor" red paddy soil, the total amount of water-soluble potassium and exchangeable potassium also decreased significantly in the early stages of rice cultivation (within 0-100 years), reaching very low levels (about a 30% decrease). Subsequently, the transformation thresholds between water-soluble potassium and exchangeable potassium, and between exchangeable potassium and non-exchangeable potassium, stabilized, with thresholds remaining between 32±4 and 64±4 mg·kg-1, respectively. 【Conclusion】During the formation of paddy soils, the potassium forms and transformation thresholds in these soils are closely related to the potassium-rich minerals in clay and silt particles. The potassium release mechanisms of layered silicate potassium-rich minerals can remain stable over a long period during the formation of "potassium-rich" paddy soils. For red paddy soils, especially those with over 200 years of rice cultivation, it is necessary to increase potassium fertilizer input in a sustainable and potassium-balanced manner to avoid negative potassium balance in the fields. There is great potential in using gravel-rich layered silicate potassium minerals as an alternative to traditional potassium fertilizers in paddy fields.

      • Research Progress and Hotspot Analysis of Long-distance Electron Transport and Environmental Effects of Cable Bacteria

        LIU Hao, WANG Zhijie, LIU Dandan, HUANG Lingyan

        DOI: 10.11766/trxb202406070226

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        Abstract:

        Cable bacteria, a recently discovered type of microorganism found in marine and freshwater sediments, have the unique ability for long-distance electron transfer. Their capacity to link sulfide oxidation in deep anoxic layers with oxygen reduction in surface aerobic layers over spatial distances has garnered significant attention. This electron transfer not only influences sediment pH migration but also affects sediment potential, creating electric fields that impact the cycling of various elements in sediments, thus influencing the ecological environment. Research on cable bacteria"s electron transfer and environmental effects has been prominently featured in top international journals like Nature and PNAS, making it a current research focus. This article summarizes existing research on cable bacteria, covering their classification, habitats, structural characteristics, motility, electron transfer abilities, and environmental impacts. Through bibliometric methods, the literature is analyzed to identify current research trends and future directions, providing insights for further exploration of cable bacteria"s physiological traits and environmental effects.

      • Effects of Microplastics with Different Concentrations and Particle Sizes on N2O Emissions from Agricultural Soils Under Different Temperature Conditions

        SHI Mengxuan, LI Haochen, ZHOU Pengyu, WAN Quan, CHEN Zonghai, LI Yige, LU Ying, LI Bo

        DOI: 10.11766/trxb202406040221

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        Abstract:

        【Objective】Microplastic (MP), with its small size and low degradability, is recognized as a potential persistent organic pollutant in terrestrial ecosystems. MP enters terrestrial ecosystems and affects the soil nitrogen cycling process by changing the soil’s physical, chemical, and biological properties. These changes affect soil N2O emission. Despite having gained global attention, the key factors and mechanism of MP influence on soil N2O remain unclear. Therefore, this study aimed to investigate the effects of MP size and concentrations on N2O emission from agricultural soils at different temperatures and thus explore their potential mechanism. 【Method】Agricultural soils were collected from plots in South China for indoor culture experiments, and five different treatment sets were selected under three temperature gradients (10 ℃, 20 ℃ and 30 ℃): (1) no microplastics (CK); (2) addition of microplastics with a mass concentration of 0.1% and a particle size of 74 μm (Nlp-0.1%); (3) addition of microplastics with a mass concentration of 0.5% and a particle size of 74 μm (Nlp-0.5%); (4) addition of microplastics with a mass concentration of 0.1% and a particle size of 25 μm (Nsp-0.1%); and (5) addition of microplastic with 0.5% mass concentration and a particle size of 25 μm (Nsp-0.5%). Afterward, soil N2O concentration as well as inorganic nitrogen and microbial functional genes were determined. 【Result】Elevated temperature significantly increased soil N2O emissions from agricultural soils (P < 0.001), and the cumulative soil N2O emissions at 30 ℃ were 43.3 and 6.3 times higher than those at 10 ℃ and 20 ℃, respectively. In addition, soil NO– 3-N content gradually increased with increasing temperature. The abundance of AOB amoA, Comammox (com2), nirS, nirK, and nosZ functional genes was the highest at 20℃ and lowest at 30℃. The effects of MP of different sizes on soil N2O emissions and related nitrogen cycle functional genes varied widely. Compared with the CK treatment, the Nlp treatment significantly increased soil N2O emission by 37.5% and 838.7% at 10 ℃ and 20 ℃ (P＜0.001). The Nsp treatment significantly decreased the abundance of com2 and nirK functional genes but significantly increased the abundance of nirS functional genes in soil (P＜0.001). The correlation and random forest analyses showed that soil N2O emission was significantly and positively correlated with temperature and the concentration of NO– 3-N, but significantly and negatively correlated with the abundance of AOA amoA, nirK, nirS, and nosZ functional genes (P＜0.05). Furthermore, it was observed that the nosZ functional genes and temperature were the main factors affecting soil N2O emission. 【Conclusion】Elevated temperatures significantly increased N2O emissions from agricultural soils, and different particle sizes and concentrations of MPs had different effects on soil N2O emissions, and there was an interaction effect between microplastics and temperature. The results of this study can provide a scientific basis for investigating the mechanism of MP on N2O emissions from agricultural soils under global warming conditions and for risk assessment.

      • The Biocontrol Effect and Microecological Mechanism of Lysobacter enzymogenes Bio-organic Fertilizer on Salvia miltiorrhiza Root Rot

        YOU Chuan, ZHANG Chi, YUAN Ruoyu, MEI Xinlan, WANG Xiaofang†, XU Yangchun, SHEN Qirong, WEI Zhong

        DOI: 10.11766/trxb202406250260

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        Abstract:

        【Objective】Salvia miltiorrhiza Bunge, commonly known as Danshen, is a perennial herbaceous plant that is a traditional and widely used medicinal herb in China. Intensive cultivation has led to frequent outbreaks of soil-borne diseases, notably root rot, which significantly limits the yield and quality of Danshen. 【Method】This study compared the antagonistic abilities of four Lysobacter strains isolated from the rhizosphere of Solidago canadensis against the root rot pathogen Fusarium oxysporum 220. To identify the most efficient fermentation substrate for the selected strain, microbial solid-state fermentation was conducted using tobacco stalk, rice straw, sorghum straw, corn straw, and Solidago canadensis straw. Based on the optimal fermentation substrate, a bio-organic fertilizer (BOF) was prepared. Subsequently, pot experiments were conducted to evaluate the effectiveness of this BOF in controlling Danshen root rot. Finally, based on metagenomic sequencing, the key microbial groups and functional genes enriched by BOF were analyzed. 【Result】The results of the study demonstrated that the Lysobacter enzymogenes strain Le395 exhibited strong antagonistic effects against the root rot pathogen F. oxysporum 220. In the organic fertilizer raw material screening experiment, it was found that the optimal fermentation substrate for strain Le395 was Solidago canadensis straw. In the pot experiment, it was observed that the application of the BOF effectively controlled Danshe root rot disease. Compared to the control group (CK), the disease incidence was reduced by 50.3%, and the disease index decreased by 50.2%. Additionally, the BOF showed significant growth-promoting effects. The above-ground fresh biomass of the plants treated with BOF increased by 163.1%, while the below-ground fresh biomass increased by 147.0% compared to the CK group. Finally, qPCR and metagenomics sequencing analyses revealed that the application of Le395 BOF significantly decreased the abundance of Fusarium and F. oxysporum in the rhizosphere of Danshen. It also increased the abundance of Lysobacter and L. enzymogenes, while modulating the rhizosphere microbial community structure and enhancing the abundance of disease resistance- and growth promotion-related functional genes in the rhizosphere. 【Conclusion】These findings provide a theoretical and technical foundation for developing an ecological and sustainable strategy for controlling Danshen root rot using bio-organic fertilizer.

      • Study on Soil Aggregate Stability and Influencing Factors in Granite Benggang Area of Southeast Guangxi

        PENG Ziye, XIE Meixia, LIN Xingchi, DING Erdongzi, LIU Chuhan, HE Lin, LIN Zhe, DUAN Xiaoqian

        DOI: 10.11766/trxb202405020182

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        Abstract:

        【Objective】Soil aggregate is the basic unit of soil structure, and its stability is an important index to evaluate soil erosion. This study aimed to evaluate the stability and influencing factors of soil aggregates in the granite Benggang area, explore the relationship between aggregate stability and Benggang erosion, and provide a scientific basis for the prevention and control of Benggang erosion. 【Method】In this study, the typical Benggang in the granite area of southeastern Guangxi was taken as the research object. The dry sieving method and Elliott wet sieving method were used to determine the particle size distribution of soil aggregates in the Benggang erosion area, and the soil samples containing coarse particles were desanded to further analyze the effect of aggregate stability on Benggang erosion. 【Result】The results showed that: (1) The soil mechanically stable aggregates in the granite Benggang area were mainly >2 mm, and the water-stable aggregates were mainly <0.25 mm. The wet sieve average mass diameter of soil aggregates decreased first, then increased and then decreased with the deepening of soil layer. The sanding correction of granite soil reduced the wet sieve error, and the disaggregate reduction decreased with the increase of soil depth, indicating that the stability of deep soil aggregates was poor. (2) The results of correlation analysis showed that the average mass diameter, macro-aggregate content, and disaggregate reduction were significantly positively correlated with soil organic matter, free iron oxide content, silt and clay content, and significantly negatively correlated with pH and sand content. (3) Utilizing redundancy analysis, the study identified that organic matter content and clay content accounted for 89.82% and 7.64% of the variation in soil aggregate indicators, respectively, and explained 97.46% of the total variance. Increasing the levels of soil organic matter and clay content can significantly enhance the stability of soil aggregates, thus mitigating the risk of Benggang erosion. 【Conclusion】This study clarified the stabilization mechanisms of aggregates in the granite red soil region and their influence on Benggang erosion and provides a scientific basis for regional ecological security and sustainable agricultural development.

      • Effects of Organic Fertilizer Combined with Antibiotics on C and N Erosion Loss of Purple Soil Slope

        FENG Hua, FANG Linfa, WU Changjie, XIAO Ran, LANG Ming, DENG Yan, Prakash Lakshmanan, MA Lihua, LI Zhaolei, ZHANG Fusuo, CHEN Xinping

        DOI: 10.11766/trxb202404290177

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        Abstract:

        【Objective】Partial substitution of chemical fertilizer with organic fertilizer is an effective approach for the resource utilization of agricultural wastes in China. Nevertheless environmental exposure to veterinary antibiotics from livestock manure leads to the risk of environmental pollution. Antibiotics can limit the activity of soil microorganisms that play a pivotal role in carbon (C) and nitrogen (N) cycling within soil systems. However, the combined impact of soil antibiotic residue through the soil hydraulic erosion process on soil C and N loss of slope farmland remains unclear. A deep understanding of this mechanism is important for the prevention of nutrient loss and control of non-point source pollution of slope farmland in the Three Gorges Reservoir Area. 【Method】In this study, indoor hydraulic erosion experiments with artificial rainfall were conducted to simulate the process of antibiotics"" impact on C and N erosion loss, and five treatments were set up: 1) CK, no fertilization control; 2) NP, only chemical fertilizer; 3) OMNP, organic fertilizer substituting 30% chemical phosphorus fertilizer; 4) OMNPT, oxytetracycline (OTC) contaminated organic fertilizer substituting 30% chemical phosphorus fertilizer; and 5) OMNPQ, enrofloxacin (ENR) contaminated organic fertilizer substituting 30% chemical phosphorus fertilizer. 【Result】The results showed that: (1) Compared with the application of chemical fertilizer, partial substitution of chemical fertilizer with organic fertilizer significantly reduced the hydraulic erosion of slope land; however, organic fertilizer with antibiotics exposure had no significant effect on erosion process compared to OMNP. (2) The residual concentrations of OTC and ENR in soil were 32.30 μg·kg-1 and 25.55 μg·kg-1, respectively. OTC loss was dominated by runoff (loss mass, 178.60 μg) while ENR loss was dominated by sediment (loss mass, 79.18 μg). (3) Compared with the application of chemical fertilizer only, partial substitution of chemical fertilizer with organic fertilizer significantly reduced total organic carbon (TOC) loss by 8.94% to 11.54%, mineral-associated organic carbon (MAOC) loss by 11.23% to 13.97%, total nitrogen (TN) loss by 22.00%, nitrate nitrogen (NO– 3-N) loss by 29.68%, and ammonium nitrogen (NH+ 4-N) loss by 27.81%. The application of organic fertilizer with antibiotics exposure had no significant effect on the loss of TOC, dissolved organic carbon (DOC), particulate organic carbon (POC) and MAOC, but increased the risk of soil N loss. Compared with the organic fertilizer without antibiotics, the loss fluxes of TN, NO– 3-N and NH+ 4-N in organic fertilizer with antibiotics exposure replacing chemical fertilizer were significantly increased by 22.77% to 37.73%, 19.46% to 22.77% and 190.10% to 253.38%, respectively. Also, it was observed that antibiotics altered the microbial community structure of soil and sediment, which was probably the main cause of increased soil nitrogen loss during erosion processes. (4) Pearson correlation analysis revealed that antibiotic exposure suppressed bacterial abundance and microbial biomass carbon (MBC), and promoted C and N loss. However, the two antibiotics had different effects on soil C and N loss, and only ENR exposure concentration had significant effects on TOC loss and NO– 3-N loss. Compared with the application of organic fertilizer without antibiotics, antibiotics (OTC and ENR) increased the proportion of soil C and N loss by 0.80% to 2.94% and 22.77% to 37.73%, respectively. 【Conclusion】The partial substitution of chemical fertilizer with organic fertilizer can reduce soil erosion and nutrient loss of slope land. However, this action may also result in the contamination of soil with antibiotics, which could subsequently lead to the increased nitrogen loss of slope farmland.

      • Dynamics of Soil Moisture and Its Response to Rainfall in Caragana Korshinskii Plantation in Loess Hilly Region

        LIANG Jing, WANG Guoliang, XU Xiaoyang, LIU Ying, MAO Jirong, ZENG Yan

        DOI: 10.11766/trxb202404220165

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        Abstract:

        【Objective】The seasonal dynamics of soil water and its changes along the soil depth restrict the growth and development of Caragana korshinskii plantation. Thus, by exploring the effects of precipitation types and rainfall on soil water content in the loess hilly area, this study seeks to clarify whether precipitation replenishment could meet the water demand of the growing season of Caragana korshinskii forest, and provide theoretical support for the ecological construction of artificial Caragana korshinskii forest in the loess hilly area.【Methods】The analyses in this study are based on precipitation and soil moisture data of Ansai Lime stick forest in Shaanxi Province from 2019 to 2023. The monthly dynamic changes of soil water under Caragana korshinskii forest at different depths were analyzed, and the response process of soil water to different precipitation types and rainfall during the growing season was investigated. The precipitation data was recorded every 30 minutes, and the soil water data were repeated at three monitoring points on the slope and under the slope, with the monitoring frequency of once an hour. The soil volumetric water content at 10 depths (10, 20, 30, 50, 70, 100, 200, 300, 500, 1 000 cm) was monitored. 【Results】(1) The precipitation in the study area could be divided into 5 types according to the characteristics of precipitation: light rain, moderate rain, large rain, heavy rain, and very torrential rain. Most of the precipitation events in the study area belonged to moderate rain type, with 59 events accounting for 46% of the total events. (2) Soil moisture content was affected by precipitation, and the annual variation of 0~100 cm soil moisture content showed a "double peak" pattern. In May to August, when Caragana korshinskii was growing vigorously, the seasonal dry layer appeared in the 50~100 cm soil layer. The occurrence time of the dry layer was closely related to the precipitation of the year, and the dry layer disappeared after sufficient precipitation recharge. (3) There was a significant positive correlation between rainfall type and soil water infiltration depth (R2 > 0.81), in which the infiltration depth of heavy rain and heavy rain was the deepest, reaching 100~200 cm, followed by moderate rain 10~70 cm, while light rain was limited to 0~10 cm. The response time of surface and deep soil of heavy rain was the shortest, followed by heavy rain, while the response process of light rain was relatively slow. Also, the soil water supply of rainstorm were significantly higher than that of other rainfall types, accounting for 87.5% of the secondary precipitation, followed by heavy rain (36.2%) and long-duration moderate rain (29.7%), while the precipitation of light rain and short-duration moderate rain was mostly lost in the form of evapotranspiration. 【Conclusion】(a) Most precipitation events in the study area belonged to the moderate rain type. The recharge efficiency of light rain and moderate rain was low, and more was loss in the form of evapotranspiration. Although the occurrence frequency of heavy rain was low, it played an irreplaceable role in replenishing soil water. (b) During the flourishing period of Caragana korshinskii growth in summer, the 50~100 cm soil layer generally had different degrees of seasonal drought, which adversely affected the normal growth of vegetation. However, the infiltration depth of heavy rain and rainstorm events reached approximately 50 cm and replenished soil water, and the annual precipitation could meet the needs of Caragana korshinskii growth.

      • Differential Responses of Microbial Necromass to Warming in topsoil and subsoil

        YANG Dongqiao, ZHANG Zihan, LU Mengya, DING Xueli

        DOI: 10.11766/trxb202407080274

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        Abstract:

        【Objective】Microbial necromass carbon (MNC) is an important component of the soil organic carbon (SOC) pool and probing the response of MNC to climate change is key to a deeper understanding of the mechanisms of microbial-mediated regulation of SOC formation. There is still a lack of understanding regarding the impact of climate warming on topsoil and subsoil MNC accumulation dynamics in different ecosystems. 【Method】This study conducted a meta-analysis of the effect of warming of 8 sample sites on MNC in different soil layers and its contribution to SOC and on the response of topsoil and subsoil MNC to warming (41 for total amino sugars, 69 for glucosamine, 69 for muramic acid and 26 for galactosamine). 【Result】Warming promoted the accumulation of MNC in different soil layers as a whole, especially in the topsoil (14.3%). This may be related to the differences in plant-carbon input and the spatial heterogeneity of microbial communities in different soil layers under a warming background. However, due to the acceleration of the loss of SOC in the subsoil after warming, the proportion of MNC contribution to SOC in the subsoil (12.5%) was higher than that in the topsoil (11.3%). Furthermore, the positive effect of the accumulation of fungal necromass and their contribution to SOC in different soil layers was greater than that of bacterial necromass, suggesting that the new carbon input directly or indirectly regulated the composition of MNC. Moreover, the impact of warming on the accumulation of MNC in different soil layers is bound up with warming amplitude and years. Lower warming (≤ 2℃) promoted microbial anabolism to increase the accumulation of MNC in the topsoil by 17.2%, while the contribution of MNC in increasing SOC in the subsoil pool was significantly promoted (14.7%) during higher warming (> 2℃). On the timescale of warming, long-term warming (> 5a) changed the microbial activity pattern and had a greater impact on the ratio of MNC to SOC in subsoil (42.8%). Meanwhile, the contribution of microbial necromass to SOC was increased with soil depth in forest and cropland, whereas warming weakened the proportion of subsoil microbial necromass to SOC in grassland. 【Conclusion】Based on our analysis, we suggest that research on the dynamics of microbial-mediated organic carbon accumulation in specific ecosystems in response to warming should focus on the response of microbial necromass in both topsoil and subsoils. This would provide a huge boost to understanding and predicting the sensitivity of SOC dynamics to climate change and its feedback mechanisms.

      • Stoichiometric Ratio and Influencing Factors of Soil Nutrients Under Farmland, Forestland, and Grassland in Eastern Xizang Autonomous Region

        DU Yuanyuan, ZHAO Wen, HUANG Laiming

        DOI: 10.11766/trxb202404270171

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        Abstract:

        【Objective】The investigation of soil nutrient content and stoichiometric ratios is of great significance for gaining a deeper understanding of the nutrient cycling and balance mechanisms within ecosystems. The Xizang Autonomous Region, situated on the southwestern Qinghai-Tibetan Plateau, functions both as an ecologically fragile area and a crucial ecological security barrier for China. This research examined the soil nutrient stoichiometric ratios and their influencing factors under different land use patterns in the alpine region of the Xizang Autonomous Region. The objective was to assess nutrient limitations in the study area and provide a foundation for effective nutrient management in these sensitive ecosystems. 【Method】This study focused on three land use types (farmland, forestland, and grassland) across an east-west transect in the eastern Xizang Autonomous Region. Soil samples were collected at different depths (0-10 cm, 10-20 cm, and 20-30 cm) to measure basic physical and chemical properties (including clay content (Cy), bulk density (BD), porosity (Ps), soil water content (SWC), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), Alkali-hydrolyzable nitrogen (AN) and available phosphorus (AP)). The longitude (LON), latitude (LAT), and altitude (ALT) of each sampling site were recorded using GPS, while environmental factors such as mean annual temperature (MAT), mean annual evaporation (Ea), mean annual precipitation (MAP), and vegetation normalization index (NDVI) were extracted using ArcGIS. Variance analysis was employed to assess differences in the contents of SOC, TN, AN, TP, and AP, along with their corresponding nutrient stoichiometry ratios (C:N, C:P, N:P, and AN:AP) among farmland, forestland, and grassland. Additionally, correlation analysis and redundancy analysis were conducted to identify the factors influencing nutrient stoichiometric ratios across the three land use types. 【Result】The findings revealed no significant differences in SOC, TN, or AN contents among the different land use types (P > 0.05). However, TP and AP contents in farmland were significantly higher than those in forestland and grassland. Moreover, soil C:N did not vary significantly with depth across any of the land use types. The AN: AP ratio in the 10-20 cm soil layer of grassland was significantly higher than that in farmland and forestland, while the C:P and N:P ratios in the 20-30 cm soil layer of farmland were significantly lower compared to forestland and grassland. Farmland soils exhibited greater nitrogen limitation, evidenced by lower AN contents and reduced N:P. Redundancy analysis indicated that SOC, TN, BD, Ps, MAT, and Ea were among the common influencing factors for the 0-30 cm soil nutrient stoichiometric ratios in farmland (16.2%-41.7%), forestland (17.3%-33.9%), and grassland (11.0%-26.9%). Interestingly, the influence of environmental factors on the soil nutrient stoichiometric ratios under different land use types decreased with increasing soil depth. 【Conclusion】Overall, this research enhances the understanding of the key factors influencing soil fertility under different land use types and offers valuable guidance for optimizing nutrient management in the alpine region of Xizang Autonomous Region.

      • Effects of Organic Amendments and Their Combination with Biochar on the Stability of Aggregates in Red Soil

        ZHANG Xin, WU Qifeng, ZHOU Yan, MA Xiaomin, XING Jiajia, PENG Liyuan, QIN Hua, CHEN Junhui

        DOI: 10.11766/trxb202405180201

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        Abstract:

        【Objective】This study aimed to elucidate the effects of different organic amendments (including corn straw, sheep manure, and biochar) application on the stability of soil aggregates and biological binding agents and to provide a scientific basis for carbon sequestration and fertilization improvement of red soil.【Method】The distribution of soil aggregates in different size and the contents of biological binding agents in aggregates were analyzed following six-year successive application of corn straw and sheep manure alone and in combination with biochar.【Result】Compared with the non-amended control, the contents of soil aggregates with particle size > 2 mm and 2-1 mm and the mean weight diameter (MWD) of soil aggregates were significantly increased by application of straw and sheep manure alone. In particular, the MWD and the aggregates of > 0.25 mm were significantly increased by 50% and 27.66% under straw amendment, while increased by 103.13% and 36.17% under sheep manure application alone, respectively. However, biochar alone or in combination with organic amendment did not affect the particle size distribution of soil aggregates. There were no significant interactions between biochar and the organic amendment on the particle size distribution. The organic amendment had a significant effect on the soil organic carbon (SOC) and microbial biomass carbon (MBC) content of aggregates of each particle size. Also, the contents of SOC, MBC, total glomalin-related soil proteins (T-GRSP), and polysaccharides in macroaggregates (> 0.25 mm) were significantly increased by straw, sheep manure, and biochar application alone. Compared with the sole application of straw and sheep manure, biochar co-application significantly increased the SOC content in macroaggregates by 207% and 151%, the MBC by 78% and 62%, the T-GRSP by 15% and 20%, and the polysaccharide content by 24% and 22%, respectively. Biochar and organic amendment had a significant interactive effect on the SOC and MBC content in macroaggregates, silt, and clay particles. In addition, the combined application of biochar and organic amendment had a significant interactive effect on the content of polysaccharides. Random forest regression model analysis showed that the contents of easily extractable glomalin-related soil proteins (EE-GRSP), T-GRSP, and polysaccharides in aggregates were the key factors affecting the MWD.【Conclusion】These findings suggest that long-term successive application of straw and manure could significantly increase the stability of soil aggregates by increasing the MBC, T-GRSP, and polysaccharide in the macroaggregates. The combined application of biochar can promote the accumulation of biological binding agents in macroaggregates, which is more conducive to improving the structural stability and the potential of carbon sequestration and fertilization of red soil.

      • Distribution Characteristics of n-Alkanes and Compound-specific Carbon Isotopes in Black Soil of Songnen Plain and Their Implications

        QIU Zifei, SHI Yonghui, LI Jingjing, YANG Fei, LONG Hao, ZHANG Ganlin

        DOI: 10.11766/trxb202405190202

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        Abstract:

        【Objective】Normal alkanes (n-alkanes) are relatively stable components of soil organic matter. Identifying the composition and occurrence mechanisms of n-alkanes in black soil is of great significance, as it can reveal the source of organic matter and the changes in the soil-forming environment. The purpose of this study was to evaluate the influence of soil-forming processes on the n-alkane index of black soil and to explore the indicative significance of n-alkanes in black soil.【Method】In this study, samples from three typical soil formation processes of Isohumosols in the Songnen Plain were collected, including the HL profile naturally developed under relatively stable terrain conditions, the YA profile affected by erosion and accumulation under unstable terrain conditions and the SH profile with evident animal disturbance processes. The ultrasonic extraction method was utilized to extract free n-alkanes from the soil. The distribution characteristics and compound-specific carbon isotopes were analyzed. 【Result】The results showed that the HL and YA profiles were unimodal, with the main peak being C31 and the odd-even predominance, while the SH profiles were bimodal, with the main peak being C23 and C31. The ∑C25~35 and CPI values of HL and SH sections decreased with the depth of the section, while the ∑C25~35 and CPI values of the YA section increased in the buried layer. The mean δ13Calk values of HL and YA profiles ranged from -29.30 to -30.27‰ and -29.79 to -32.60‰, respectively. Our results indicate that the buried layer is found to enhance the retention of n-alkanes, while disturbance may disrupt other indicators of n-alkanes in situ records. Furthermore, the analysis of n-alkanes and their carbon isotopes suggests that soil organic matter primarily originates from terrestrial higher plants, particularly C3 plants. Since the Holocene period, herbaceous plants dominate the black soil area of the Songnen Plain, with the proportion of woody plants gradually increasing during the development of black soil. Combining the data from 14C dating, it is inferred that the climatic conditions during the last deglaciation likely played a role in the initial development of black soil, while the warm and wet climate of the Middle Holocene contributed to the maturity of black soil.【Conclusion】These results confirm that n-alkanes in black soil can reflect the impact of soil erosion-deposition and disturbance on n-alkanes. Thus, this study will provide a basis for revealing the changes in organic matter sources during the formation of black soil and reflect the soil-forming environment of black soil.

      • Evolution Patterns and Underlying Sequestration Mechanisms of Organic Carbon Components in Soil Aggregates under Long-term Rice Cultivation

        Zhang Yingchun, Wang Ping, Liu Yalong, Wang Jingkuan

        DOI: 10.11766/trxb202402200074

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        Abstract:

        【Objective】Paddy soil is a type of anthropogenic soil formed through long-term water cultivation and ripening, which has a high organic carbon storage and carbon sequestration potential. Clarifying the protection mechanisms of organic carbon in paddy soil can provide a theoretical basis for carbon sequestration, emission reduction, and sustainable utilization of paddy soil. 【Method】Using a 1000-year chronosequence of paddy soils formed through coastal reclamation in Eastern China, we investigated the distribution characteristics and evolution patterns of occluded/free and particulate/mineral-bound organic carbon within soil aggregates under long-term rice cultivation. This was achieved through methods such as force-stable aggregate fractionation and physical particle/density grouping. 【Result】While soil organic carbon (SOC) gradually accumulated under long-term rice cultivation, the contents of particulate organic carbon (POC) and mineral-bound organic carbon (MOC) also increased. However, MOC was the dominant form, accounting for 64.40%~87.89% of the total SOC pool. The distribution patterns of different size soil aggregates were consistent, with macroaggregates (74.0%~77.6%) being the most abundant, followed by microaggregates (9.2%~15.9%) and silt and clay-sized microaggregates (8.6%~15.7%). Therefore, over 70.00% of SOC was stored in the macroaggregates. The organic carbon content of aggregates of all particle sizes increased with the increase of paddy cultivation age and grain size, which were 7.39~13.78 g·kg-1, 1.72~2.74 g·kg-1 and 0.66~1.92 g·kg-1. Among different types of soil aggregates, mineral-bound organic carbon (MOC) was the dominant form. In macroaggregates, occluded microaggregates, and free microaggregates, the MOC contents were up to 2.9, 1.1, and 3.2 times higher than POC, respectively. The protective effect of occluded microaggregates on POC was stronger than free microaggregates, with the POC content in occluded microaggregates being up to 1.5 times higher than in free microaggregates. 【Conclusion】Long-term rice cultivation is beneficial for SOC sequestration under the physical protection of soil aggregates. The protective effect of occluded microaggregates on POC is a potential mechanism for carbon sequestration in paddy soil.

      • Rapid Assessment of Critical Coagulation Concentration of Soil Colloids by Zeta Potential

        yuanlei, xuyingde, renkailu, zuoyan, lishaobo, zhangyun, zhangguangcai, wangjingkuan, gaoxiaodan

        DOI: 10.11766/trxb202403140110

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        【Objective】The sedimentation characteristics of soil colloids are intricately linked to soil fertility and erosion resistance, with the critical coagulation concentration serving as a pivotal parameter for evaluating particle aggregation and dispersion. The rapid and accurate determination of this critical coagulation concentration holds significant importance in assessing soil quality. 【Method】This study evaluates the critical coagulation concentrations of three types of particles: —montmorillonite, humic acid, and brown earth colloids, —by observing the trend in zeta potential variation on their surfaces. Through piecewise linear fitting, the feasibility of determining the critical coagulation concentration using the zeta potential method is verified in conjunction with dynamic laser light scattering. 【Result】The findings reveal that: (1) The absolute value of zeta potential in each system decreases with increasing electrolyte concentration. This decline is rapid in the relatively low electrolyte concentration range but slows down in the higher concentration range. (2) The critical coagulation concentration of montmorillonite and brown earth colloids on the charged surface in potassium and calcium ion systems determined through piecewise fitting with electrolyte concentration changes, aligns with measurements from dynamic laser light scattering. (3) However, there was a significant difference between the critical coagulation concentration measured by the zeta potential and dynamic laser light scattering methods for humic acid colloid with variable charged surface in potassium and calcium systems. 【Conclusion】For montmorillonite and brown earth colloidal particles with constant charged surfaces, the zeta potential method can be used to rapidly and accurately determine their critical coagulation concentrations. This method boasts simplicity, requires minimal sample volume, and offers high efficiency. Conversely, for humic acid colloidal particles with variable charged surfaces, the zeta potential method fails to accurately assess the critical coagulation concentration.

      • Effects of Long-term Straw Return on Soil Arbuscular Mycorrhizal Fungi and Their Ecological Network

        SHI Qihuan, Zhang Yanjie, ZHOU Guixiang, ZHANG Jiabao, ZHANG Congzhi, LU Shunbao, JIA Chunhua, LIU Mingfeng

        DOI: 10.11766/trxb202404100150

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        Abstract:

        Abstract：【Objective】Arbuscular mycorrhizal fungi (AMF) play a crucial role in soil microbial ecological networks and can form symbiotic structures with about 80% of plants, making them a key component of sustainable soil management. 【Methods】In order to reveal the response mechanism of soil AMF and their ecological network to straw return in the fluvo-aquic soil area of North China Plain, experimental plots with different straw return treatments were chosen under long-term wheat-maize rotation, and high-throughput sequencing and ecological network analyses were applied to elucidate the composition of soil mycorrhizal practices and fertilization treatments. The experiment was set up with five treatments and three replications, including T1: straw removal + PK fertilizer; T2: straw mulching + PK fertilizer; T3: straw removal + NPK fertilizer; T4: straw mulching + NPK fertilizer; and T5: straw burying + NPK fertilizer.【Results】The results showed that: (1) Straw incorporation with NPK fertilizer significantly decreased soil pH and increased the content of soil organic matter, total nitrogen, ammonium nitrogen, available potassium, and available phosphorus (P < 0.05). This suggests that the combination of straw and NPK fertilizer is effective in enhancing soil fertility. (2) Different treatments of straw burial and nitrogen fertilizer application significantly affected the community composition of AMF, however, there was no significant difference in the alpha diversity of the communities. Nevertheless, Glomus and Paraglomus were the main dominant genera of the AMF community in the fluvo-aquic soil, highlighting their important role in these ecosystems. (3) Co-occurrence network analysis revealed seven distinct ecological network modules. Notably, the species abundance in module VI showed a significant positive correlation with several soil nutrient indices, including organic matter, nitrate nitrogen, available phosphorus, available potassium, and total nitrogen (P < 0.05). This module also exhibited a significant positive correlation with N-acetylglucosaminidase activity, an enzyme involved in nitrogen cycling (P < 0.05). Conversely, the species abundance in module VI was significantly negatively correlated with soil pH (P < 0.05).【Conclusion】Different straw returning methods can effectively regulate soil fertility by improving soil physicochemical properties, modulating the structure and diversity of soil microbial communities, and adjusting AMF network interactions. By understanding the complex interactions between AMF communities and soil management practices, we can develop more effective strategies for maintaining soil health and productivity. This research provides valuable insights into the mechanisms by which straw returning and fertilization treatments influence AMF communities and their ecological networks, offering a foundation for future studies and practical applications in sustainable agriculture.

      • Effects of Different Straw Returning Methods on the Accumulation of Plant- and Microbial-derived Carbon in Shajiang Black Soil（Vertisol）

        Yu ZiZhou, Guo ZiChun, Ding TianYu, Wang YueKai, Zhang Ping, Peng XinHua

        DOI: 10.11766/trxb202406010218

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        【Objective】Soil organic carbon (SOC) is one of the key factors influencing crop yield in the Shajiang black soil region, and straw returning is an effective method for continuously improving SOC. However, the accumulation characteristics of plant- and microbial-derived carbon and their relative contribution to SOC under different straw returning methods (no-tillage with straw returning, NTS; rotary tillage with straw returning, RTS; deep ploughing with straw returning, DPS) remain poorly understood. Therefore, this study aims to explore these characteristics and contributions of plant- and microbial-derived carbon in 0~10 cm, 10~20 cm and 20~40 cm soil layers of Shajiang black soil under different straw returning methods. 【Method】A seven-year field experiment was conducted using lignin phenols and amino sugars as biomarkers. Mixed soil samples were collected from depths of 0~10, 10~20, and 20~40 cm. The content of plant- and microbial-derived carbon and their contributions to SOC were calculated based on the biomarkers content. 【Results】The results revealed that, RTS and DPS significantly increased the SOC content of each soil layer, with an increase of 113% (P < 0.05). In contrast, the effects of NTS on SOC were mainly concentrated in the 0~10 cm layer after seven years, showing a phenomenon of surface accumulation in SOC. There was no significant difference in lignin phenol content between NTS and RTS (P > 0.05), however, in the 10~20 cm and 20~40 cm layers under DPS treatment, lignin phenol content increased by 57.3% and 36.3%, respectively (P < 0.05), despite a marked decrease in the 0~10 cm layer (P > 0.05). Additionally, the relative contents of Vanillyl (V) and Syringyl (S) phenols under DPS were significantly increased (P < 0.05) and the degree of oxidative degradation of lignin in the 10~40 cm layer was lower than that under NTS and RTS. Furthermore, amino sugar content showed no significant difference between NTS and RTS in each soil layer. However, under DPS, amino sugar content in the 10~20 cm and 20~40 cm layers increased by 45.6% and 35.8% in comparison with RTS, respectively (P < 0.05). The variation trend of Glucosamine (GluN) and Galactosamine (GalN) with soil depth was similar to amino sugar content, but in the 0~20 cm layer, Muramic acid (MurN) content under NTS and DPS was lower than that of RTS, with a highest decrease of 47.2%. Interestingly, DPS promoted the transformation of microbial community towards fungi, with the carbon ratio of fungal necromass to bacterial necromass in the 10~20 cm and 20~40 cm layers increasing by 177% and 58.0%, respectively, compared to RTS (P < 0.05). 【Conclusion】The substantial increase in SOC content primarily results from a significant rise in crop residue content observed in the topsoil (0~10 cm) under NTS and RTS, as well as in the deeper soil (10~40 cm) following DPS. Our findings suggest that DPS promotes the accumulation of plant- and microbial-derived carbon in deeper soil layers, increases the contribution of microbial carbon to SOC and enhances the stability of carbon pool, which is crucial for the efficient utilization of straw resources and improvement of soil quality in Shajiang black soil region.

      • Effect of Nitrogen and Phosohorus Addition after Straw Input on the Microbial Community Structure and the Accumulation of Necromass in Paddy Soil

        LU Mengya, WANG Zhiquan, ZHANG Kun, DING Xueli

        DOI: 10.11766/trxb202406220253

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        Abstract:

        【Objective】Paddy soil has enormous potential for carbon sequestration and straw inputs in these soils strongly influence the microorganism-mediated turnover of soil organic carbon (SOC). This study aims to explore the microbial processes involved in the formation of SOC in response to straw inputs and to determine the regulatory effects of nitrogen and phosphorus on these microbial processes. 【Method】A 300-day laboratory experiment was conducted to investigate the effects of straw (S) and straw combined with nitrogen and phosphorus nutrient additions (S+NP) on soil microbial communities and their necromass accumulation processes, in a subtropical red loam rice soil. Phospholipid fatty acids (PLFA) and amino sugars (AS) were used as microbial biomarkers to indicate living microbial biomass community and necromass, respectively. 【Result】The results showed that compared to the control (CK) treatment, the S and S+NP treatments significantly increased the total soil PLFA content (P < 0.05) and the increase in fungal biomass (65.1%-30.1%) was greater than that of bacterial biomass (22.6%-34.3%). Fungal biomass was significantly higher in the S+NP treatment than that in the other treatments at the later incubation stage of 300 d, and the ratio of fungal/bacterial biomass (F/B) also significantly increased in straw plus high rate of nutrient supply (P < 0.05). Our results suggested that nitrogen and phosphorus application may affect soil microbial community structure over a longer time after straw amendment, which gradually shifted towards a fungal-dominated community structure with time. The accumulation of microbial necromass was significantly higher in both S and S+NP treatments than in the control throughout the incubation period (P < 0.05), and the dynamics of fungal necromass mirrored the total microbial necromass. However, bacterial necromass reduced remarkably at the end of the incubation and their content was significantly lower in the S+NP treatment than that in the S treatment (P < 0.05), suggesting its decomposition in the later stages of incubation. Further correlation analysis showed significant positive correlations between microbial biomass, microbial necromass and SOC (P < 0.05). This demonstrates the importance of microbial mediated mechanisms driving SOC formation and transformation in paddy fields following exogenous straw application. 【Conclusion】In conclusion, the impact of straw return on soil organic carbon pool in paddy fields is closely related to microbial community structure and its mediation of necromass accumulation process, which may be regulated by extraneous nutrient supply. Furthermore, supplementation with moderate amounts of nitrogen and phosphorus nutrients can facilitate the accumulation of organic carbon fractions of microbial origin over longer time scales, especially the fungal necromass carbon. This will be of significant importance in regulating microbial-mediated organic carbon sequestration processes through on-farm nutrient management practices.

      • Research Progress on Ecological Effects and Microbial Degradation of Biodegradable Plastics in Soils

        HAN Yujuan, TENG Ying

        DOI: 10.11766/trxb202405270210

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        Abstract:

        Biodegradable plastics are considered ideal replacements for traditional plastics due to their easy biodegradability, and have broad application prospects. Soil is an important destination for various biodegradable plastic waste. A comprehensive understanding of the ecological effects of biodegradable plastics in the soil environment can provide a scientific basis for evaluating the ecological safety of biodegradable plastics, which is the foundation and prerequisite for their large-scale promotion and application. Given that microbial degradation is the main pathway for the degradation of biodegradable plastics in soil, a thorough understanding of the degradation process and mechanism can provide theoretical guidance for achieving efficient and controllable in-situ degradation of biodegradable plastics. This paper first summarized the ecological toxicological effects of biodegradable plastics on soil ecosystems from the perspectives of soil physicochemical properties, soil microorganisms, plants, and animals. Biodegradable plastics entering the soil environment are not only a physical input, but also a chemical input, which can change the physicochemical properties of soil, such as bulk density, porosity, and nutrient content. They can directly or indirectly affect the structure and function of soil microbial communities, and affect the growth and development of plants as well as the survival and reproduction of soil animals. Furthermore, the microbial degradation mechanism of biodegradable plastics in soil and the key factors affecting degradation efficiency were further summarized. Soil microorganisms degrade biodegradable plastics mainly through three key steps: colonization on the plastic surface, secretion of extracellular enzymes that catalyze polymer depolymerization, and mineralization of oligomers or monomers. The degradation rate of biodegradable plastics in the actual soil environment is relatively slow, and their degradation efficiency is affected by various factors such as the properties of plastics, soil environment, and climate conditions. At the same time, the microorganisms and enzymes involved in the degradation of biodegradable plastics were systematically combed. Because of the current research status and shortcomings, the key research directions in the future are prospected, aiming to provide scientific reference for the study of environmental impacts and microbial degradation of biodegradable plastics in soil.

      • The Synergistic Effect of a Phage-Probiotic Combination on Suppressing Bacterial Wilt Disease

        XI Ningbo, WANG Shuo, LI Tingting, WANG Xiaofang, XU Yangchun, SHEN Qirong, WEI Zhong

        DOI: 10.11766/trxb202405160200

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        Abstract:

        【Objective】Bacterial wilt disease, caused by soil-borne Ralstonia solanacearum, has led to significant yield reductions or even crop failures in tomatoes, potatoes, and tobacco, severely limiting the safe supply of agricultural products. Rhizosphere microorganisms play a crucial role in mitigating soil biotic impediments. Probiotics can inhibit pathogens through antagonism or nutrient competition, while phages can target pathogens through specific infections. However, the single use of either probiotics or phages often results in unstable effects, and the high-density fermentation cost of these strains is considerable. 【Method】To establish an efficient and stable technology for reducing soil biotic impediments, this study constructed combinations of antagonistic-competitive and nutrient-competitive beneficial bacteria with phages. It explored their synergistic effects in reducing soil wilt disease through in vitro microplate and greenhouse pot experiments. The potential mechanisms of synergy between probiotics and phages were also investigated. 【Result】 The results showed that most combinations of phages and probiotics exhibited synergistic effects, significantly enhancing the inhibition of pathogenic R. solanacearum growth and the reduction of bacterial wilt disease. Notably, the combination of the antagonistic-competitive beneficial bacterium T-5 with phages resulted in an 89.19% reduction in pathogenic bacterial growth compared to the control. Greenhouse experiments indicated that the synergistic effect reduced the disease index by an average of 58.18%, with the combination of the nutrient-competitive beneficial bacterium WR21 and phages significantly reducing the disease index by 67.28%. Further studies revealed that even at lower concentrations of beneficial bacteria, the phage-bacteria synergy remained effective. At a concentration of 104 CFU?g-1 substrate, the combination of T-5 with phages reduced the disease index by 21.56% and the number of rhizosphere pathogenic bacteria by 19.21% compared to the application of beneficial bacteria alone, demonstrating a strong synergistic effect. Additionally, the study explored the impact of phage-beneficial bacteria combinations on the characteristics of pathogenic R. solanacearum. The results showed that the phage-nutrient-competitive beneficial bacteria combination significantly reduced the pathogen""s carbon source utilization ability, with the WR21 and phage combination reducing the number of carbon sources utilized by the pathogen by 87.9%. Furthermore, under the dual stress of phages and antagonistic-competitive beneficial bacteria, the sensitivity of the pathogen to the antagonistic substances produced by T-5 increased by 64.10%. 【Conclusion】This study highlights the potential of phage-beneficial bacteria combinations in mitigating bacterial wilt disease and preliminarily elucidates the potential mechanisms behind their synergistic effects. These findings provide theoretical and technical support for the development of efficient soil biological obstacle reduction techniques.

      • Effects of Folsomia candida on Soil Microaggregates Under Different Nitrogen Addition

        YOU Lelin, ZHANG Tingting, DAI Wencai, XIAO Naichuan, ZHAO Huan, ZHANG Yarong, XIE Jun

        DOI: 10.11766/trxb202404080148

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        Abstract:

        【Objective】This study aimed to investigate the impact of different nitrogen fertilizer application rates on the growth and reproduction of Folsomia candida and their effects on soil micro-aggregates.【Method】Soil samples from field experiments with varying nitrogen application rates (N0: 0 kg·hm-2, N90: 90 kg ·hm-2, N180: 180 kg·hm-2, N270: 270 kg·hm-2, N360: 360 kg·hm-2) were cultivated to examine the differences in Folsomia candida reproduction, total body weight, and their effects on soil micro-aggregates over different cultivation periods (28 d, 42 d, 56 d).【Result】The results indicated that nitrogen application significantly affected soil pH, with the N360 treatment showing a decrease of 0.9 pH units compared to the N0 treatment (P < 0.05). The reproduction of Folsomia candida showed significant differences among the nitrogen treatments as the cultivation period extended. After a 56 d cultivation period, the reproduction number in the N0 treatment was 1.10-1.53 times higher than that in the other treatments (P < 0.05). The total biomass of Folsomia candida larvae generally followed the same trend as the reproduction, with the lowest values observed in the N360 treatment across all cultivation periods. Also, Folsomia candida significantly increased the quantity of 0.05-0.01 mm micro-aggregates by 11.3%-48.4% compared to the untreated soil samples, and significantly decreased the quantity of 2-0.25 mm small aggregates by 27.9%- 60.9%, with more pronounced effects as the cultivation period extended (P < 0.05). The mean weight diameter (MWD) and geometric mean diameter (GWD) of soil under all nitrogen treatments were significantly lower than those of the untreated soil samples (P < 0.05).【Conclusion】The growth and reproduction of Folsomia candida were inhibited by nitrogen fertilization, and high densities of Folsomia candida can increase the content of soil micro-aggregates but destroy small aggregates, leading to reduced soil stability. The results of this study will provide a scientific reference for improving soil structure.

      • Dynamic Changes of Microbial Community Metabolisms Along Soil Profile in Response to Exogenous Carbon and Nitrogen Addition in Mollisols

        HU Yaohua, CAI Yuanfeng, CAO Weiwei, JIA Zhongjun

        DOI: 10.11766/trxb202402040062

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        Abstract:

        【Objective】 Soil profile is a model system for deciphering the formation and maturation of organic matter-centric fertility. However, the physiological metabolic potential of the soil profile microbial community and the mechanism of its transformation of labile carbon are not clear.【Method】The metabolic mechanisms of soil microbial communities under exogenous carbon and nitrogen input scenarios were investigated by using 13C-labeled glucose and ammonium nitrate to cultivate soils in the surface (0~10 cm), middle (30~40 cm), and deep (90~100 cm) layers of a typical thin-layered black soil. The insoluble organic carbon (13C-SOC) synthesized by microbial growth and reproduction, 13CO2 produced by heterogeneous metabolism, the priming effect, the efficiency of 13C-carbon utilization, and their nitrogen limitation features were determined.【Result】The increase in soil respiration intensity after exogenous 13C-glucose addition was in the order of surface (3.2-fold), middle (11.3-fold), and deep soil (14.5-fold) compared to the control water treatment; the relative priming effect was 43.5%, 150.5%, and 267.0%; carbon utilization efficiency was 34.9%, 37.3%, and 32.9%, respectively. Approximately 45%~50% of glucose was isomerized and metabolized to 13CO2. Also, the number of soil microorganisms increased by about 85.0% in the surface and middle layers and 1.9 times in the deep layer while the 13C-SOC of insoluble cellular biomass synthesized by microorganisms using glucose was 111.6±11.7 mg kg-1 (surface soil), 119.5±3.4 mg kg-1 (middle soil), and 105.2±21.6 mg kg-1 (deep soil). However, the proportion of the total soil organic carbon, in descending order was 0.98% (surface layer) < 1.70% (middle layer) < 4.76% (deep layer). Interestingly, the 13C-SOC tended to increase after nitrogen addition although it was not statistically differentiated, however, it significantly suppressed the relative priming effect. High-throughput sequencing revealed that surface, middle, and deep soil microbial communities clustered independently regardless of carbon and nitrogen treatments under glucose addition conditions. Micrococcaceae were significantly increased in the surface soil and were probably the main contributor of organic carbon from insoluble microbial sources whereas Nocardioides were the main contributors of organic carbon from microbial sources in the middle and deep soil.【Conclusion】These results suggest that the deep soil, despite its lower diversity and abundance, can utilize exogenous and readily decomposable organic carbon to rapidly colonize and produce insoluble organic carbon of microbial origin and its total new carbon inputs were almost identical to those of the surface soil. Soil microbial communities in black soil profiles developed strong functional plasticity during long-term adaptation to geo-climatic variability, which provides an important basis for the stability of soil ecosystem structures and functions.

      • Effects of Bacterial Residue Organic Fertilizer on Tomato Growth and Soil Antibiotic Resistance Genes Accumulation

        CUI Gege, ZHANG Yaozhong, YANG Tianjie†, WANG Shimei, HUANG Yishuo, XU Yangchun, SHEN Qirong

        DOI: 10.11766/trxb202402180072

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        Abstract:

        【Objective】Bacterial residue is a solid waste produced during the fermentation process of antibiotic synthesis intermediate (6-aminopenicillanic acid). Improper treatment will endanger environmental safety and increase the risk of the spread of antibiotic resistance genes (ARGs). At present, composting is the main method for treating residues due to its harmless and resourceful characteristics. Thus this study was designed to investigate the effects of composted bacterial residue organic fertilizer on tomato growth and soil ARGs accumulation and to assess the ecological risks of residue organic fertilizer. 【Method】In a field experiment, the tomato plant was used as the research object and the effects of organic fertilizer fermented from bacterial residue of penicillin synthesis intermediates on tomato growth, soil physicochemical properties, bacterial community structure, and the diversity and abundance of antibiotic resistance genes were analyzed【Result】The results showed that the application of residue organic fertilizer can increase the aboveground dry biomass of tomatoes in the field, and continuous application for two seasons can increase the vitamin C content of tomato fruits and soil nitrate nitrogen content. After being treated with organic fertilizer, there was no significant change in the diversity of bacterial communities in the rhizosphere soil. However, compared with conventional fertilization, the abundance of Proteobacteria significantly increased, while the abundance of Chloroflexi significantly decreased. There was no significant change in the diversity of ARGs in tomato soil after the application of residue organic fertilizer, but the amino glycoside resistance gene aada1 and sulfonamide resistance gene sul (II) were significantly higher than those in conventional compound fertilizer treatment. Also Luteimonas sp. was positively correlated with tetracycline, aminoglycoside, and sulfonamide resistance genes. 【Conclusion】After applying microbial residue organic fertilizer in tomato rhizosphere soil, there was no enrichment of β-lactam ARGs. However the risk of accumulation of tetracycline, aminoglycoside, and sulfonamide ARGs in rhizosphere microorganisms needs further evaluation.

      • Variation of the Increased CH4 Emissions in Paddy Fields with Straw Incorporation across 11 Consecutive Years

        YANG Zhengyu, LI Zongming, LI Yanyan, SHEN Jianlin, WU Jinshui

        DOI: 10.11766/trxb202402230076

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        Abstract:

        【Objective】 This study aimed to explore the variations of the increased methane (CH4) emissions and its mechanisms in paddy fields with straw incorporation across 11 consecutive years, so as to provide a scientific basis for the accurate assessment of CH4 emissions under long-term straw incorporation.【Method】A typical double-cropping rice field in the subtropical region was selected as the research subject, and the fertilizer only treatment (CON), low amount of straw incorporation treatment (3.0 t?hm-2, LS) and high amount of straw incorporation treatment (6.0 t?hm-2, HS) were set up. The field experiment was conducted for 11 years (2012—2022) with CH4 fluxes and related soil and environmental factors measured in the early and late rice seasons across the 11 years.【Result】The results showed that in the 11th year of straw incorporation, CH4 emissions in both the LS and HS treatments were substantially higher than those in the CON treatment, with the highest emissions recorded in the HS treatment, followed by the LS and then the CON treatment (HS > LS > CON). However, it was noted that the increment in CH4 emissions due to straw incorporation in the 11th year had diminished by 75.1% and 83.5% when compared to the increment in the first year (P < 0.05). In the 11th year, the contents of soil organic carbon (SOC), ammonium nitrogen (NH4+-N), and dissolved organic carbon (DOC) in the LS and HS treatments showed significant increases by 7.90% and 20.8% (LS and HS treatments, the same as below), and 15.0% and 25.7%, 19.5%, and 31.3%, respectively, compared to the CON treatment (P < 0.05). However, the redox potential (Eh) and soil bulk density (BD) exhibited significant reductions of 14.1% and 21.7%, and 10.3% and 7.76%, respectively (P < 0.05). Furthermore, the abundance of the mcrA and pmoA genes, which are instrumental in methanogenesis and methane oxidation processes, respectively, as well as the mcrA/pmoA gene ratio, were significantly enhanced in the LS and HS treatments compared to the CON, which increased by 96.0% and 152%, 12.7% and 34.8%, and 73.9% and 85.8%, respectively (P < 0.05). Through redundancy analysis, it was determined that in the 11th year of straw incorporation, CH4 emissions in the paddy field displayed a significant positive correlation with the abundance of mcrA and the mcrA/pmoA ratio in the soil (P < 0.05). The decrease in BD and the rise in Eh, induced by the increase in SOC content, likely fostered the augmentation in pmoA gene abundance, which might be the principal reason for the undermined increase in CH4 emissions for the straw treatments observed in the later stages of the experiment.【Conclusion】 In the subtropical regions, relative to CON, the increases in CH4 emissions under long-term straw incorporation was reduced by approximately 80% (P < 0.05) compared to the increase under short-term straw incorporation due to the changes in SOC, BD, and Eh. Therefore, the assessment of CH4 emissions from paddy fields with straw incorporation needs to be dynamically adjusted according to the year of duration of straw incorporation.

      • Hot Moments and Hot Spots and the Associated Influencing Factors of Denitrification along Farmland Soil Profiles in Southern China

        Zhou Han, Wang Xiaomin, Wei Zhijun, Ma Xiaofang, Zhang Yumeng, Shan Jun, Yan Xiaoyuan

        DOI: 10.11766/trxb202401020003

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        Abstract:

        【Objective】Denitrification is the primary pathway for removing NO3?-N in agricultural soil profiles, converting NO3?-N into N2, and reducing the risk of NO3?-N accumulation. However, due to methodological limitations, previous studies have mainly focused on the accumulation patterns in soil profiles or the transformation of NO3?-N in the surface soil, with less attention to its removal throughout the entire soil profile. Thus, the rate of denitrification and absolute amount of nitrate removal capacity along the soil profile remain unclear. Furthermore, the existence of “hot moments” and “hot spots” for denitrification in soil profiles is still unknown. 【Method】To evaluate the NO3?-N removal capacity of typical farmland profiles in southern China and to explore the hot moments and hot spots of denitrification, paddy fields (rice-wheat rotation), vegetable fields, and vineyard in the Taihu Lake region were selected for this study. Near in-situ incubation of flooded and non-flooded layers of the soil profile (0-300 cm) of these fields was performed using the Membrane Inlet Mass Spectrometer (MIMS) and Robotized continuous flow incubation system (RoFlow) over a year.【Result】Our results showed that the soil denitrification rate exhibited distinct hot moments and hot spots across the three planting patterns. Denitrification hot moments in rice fields were primarily observed in October during the rice season, with a rate of 17.6±1.0 nmol N g?1 h?1. The denitrification hot moments of vegetable fields and orchards mainly occurred in March, with rates of 44.2±2.5 nmol N g?1 h?1 and 45.3±7.5 nmol N g?1 h?1, respectively. The hot spots of denitrification in the paddy field occurred in the topsoil (0-20 cm) with an average rate of 3.4±0.4 nmol N g?1 h?1. The denitrification hot spots of the vegetable field and orchard mainly occurred at 20-100 cm, with average rates of 11.7±1.3 nmol N g?1 h?1 and 9.4±2.3 nmol N g?1 h?1, respectively. Also, the removal rate of NO3?-N in these denitrification hot spots exceeded 90%, and almost all NO3?-N in the soil profile was removed under the three planting patterns. Correlation analysis results indicated that the soil NO3?-N content was the primary limiting factor for denitrification. 【Conclusion】Our study reveals that the farmland soil profiles under the three planting patterns in the Taihu Lake area exhibit high denitrification rates with distinct denitrification hot moments and hot spots, effectively removing NO3?-N from the soil profile. These findings deepen our understanding of the NO3?-N removal process in farmland soil profiles, holding significant implications for accurately assessing the cumulative risk and removal capacity of NO3?-N in high N input areas of southern China.

      • Progress of soil temperature prediction equation

        Zhang Jianbin, Gao Zhi Qiu, Tong Bing, Wang Linlin

        DOI: 10.11766/trxb202210220581

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        Abstract:

        Soil temperature (especially surface temperature) is a key physical quantity in the interaction between land and atmosphere, and plays a very important role in the earth system. Soil temperature prediction technology has always been the core scientific problem in land surface model, numerical weather prediction and climate prediction. This paper systematically reviews the research progress of soil temperature prediction equation, from the classical heat conduction equation to the heat conduction convection equation that takes into account the physical process of vertical movement of soil moisture, from the single sine wave approximation to the Fourier series approximation of the daily change of surface temperature, from the assumption that the diurnal change of convection parameters is constant to the consideration of its diurnal change, and emphatically summarizes the creation, improvement and solution of the soil heat conduction convection equation. Finally, this paper reviews the application of heat conduction convection equation in the study of surface energy balance, vertical movement of soil moisture, water flux, earthquake and frozen soil heat transfer. At the same time, it is pointed out that the influences of soil water phases and plant roots on the heat conduction-convection equation is warranted for the future research of soil temperature prediction equation.

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Supervisor： Chinese Academy of Sciences

Sponsor：Soil Science Society of China

Editor-in-Chief：Xu Renkou

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Zip Code：210008

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Email：actapedo@issas.ac.cn

ISSN：0564-3929

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