Abstract:Focusing on three second-level application codes (D0701 Environmental Soil Science, D0709 Fundamental Soil Science, and D0710 Soil Erosion and Soil Fertility) managed by the discipline of environmental geosciences in Department of Earth Sciences affiliated to National Natural Science Foundation of China, this article introduced and analyzed the application, acceptance, peer review, grant funding, research teams, and key words of projects including General Program, Young Scientists Fund, Fund for Less Developed Regions, National Science Fund for Distinguished Young Scholars, Excellent Young Scientists Fund, and Key Program in 2024.

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.

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.

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(P_i), 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 P_i 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 P_i. 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.

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.

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.

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.

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.

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.

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.

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.

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.

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. SiteWise^TM 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 SiteWise^TM 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.

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.

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 (MgCl_2,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.

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.

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.

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.

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 (AI_mod), 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.

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.

Abstract:【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.

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.

Abstract:【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.

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.