Abstract:Soil organic carbon (SOC) is the largest carbon pool in terrestrial ecosystems and plays a key role in preventing soil degradation, conserving soil health, and addressing global climate change. Soil minerals are important component of the soil solid phase, and their interaction with soil organic carbon directly affects soil interfacial activity, physicochemical properties, and fertility status. The concept of mineral carbon pump (MnCP) emphasizes the crucial role of soil minerals in driving the active organic carbon sequestration, and elaborates on the function of minerals in the process of soil organic carbon stabilization. This review takes the mineral-mediated soil carbon sequestration process as the main line, systematically sorts out the concept of MnCP, introduces in detail the five MnCP-mediated carbon sequestration mechanisms, influencing factors, and related characterization techniques. Key scientific issues that need further exploration within the MnCP framework are proposed in the end.

Abstract:Soil fauna constitutes a vital component of soil ecosystems and plays a crucial role in ecosystem functioning. The high temperature caused by global warming will cause damage to soil fauna and affect their ecological functions. In addition, chemical pollutants released by human activities can also have toxic effects on soil fauna. Hydrophobic organic compounds (HOCs) are a kind of widely prevalent class of pollutants in soil. The combined effects of high temperatures and HOCs can impact soil fauna, and the tests for HOC risk assessment are typically conducted at optimal temperatures for the test species, resulting in inaccurate outcomes due to the disregard of temperature effects. Currently, there is a lack of in-depth understanding of the combined effects and mechanisms of high temperatures and HOCs on soil fauna. Therefore, we systematically reviewed the studies on the combined effects of different high-temperature scenarios and HOCs on soil fauna, and the significance of these studies in environmental risk assessment. Our discussion highlights that future research should focus on the combined effects of HOCs and high temperatures in real-world scenarios, particularly at the molecular level, and enhance the development and application of ecotoxicological models. This will improve our understanding of HOCs in the natural world and refine existing methods of environmental risk assessment to better address the challenges ecosystems face under climate change.

Abstract:Colloids are among the most active components in agricultural soils and their large specific surface area and surface charge make them highly susceptible to pollutant adsorption. During the water cycle in the saturated-unsaturated zone, colloids can carry contaminants through porous media via size exclusion effects, leading to accelerated diffusion and significant impacts on groundwater quality. This paper reviews the size exclusion mechanisms of colloid transport in porous media, systematically analyses the key factors influencing the size exclusion effects of colloid transport, and summarizes the mathematical models used to describe the size exclusion effect of colloid transport. Finally, it explores high-precision tracer methods for characterizing colloid transport behavior and discusses strategies for constructing mathematical models to depict size exclusion effects in colloid transport. This study holds significant implications for deepening the understanding of environmental effects associated with colloid transport in the saturated-unsaturated zone water cycle and guiding the prevention and control of groundwater pollution in farmlands.

Abstract:【Objective】 Soil erosion is a major factor causing soil degradation and crop productivity reduction in the northeast black soil region. However, the in situ systematic and quantitative assessment of the effects of erosion on soil quality and crop productivity remains unclear. 【Method】 A long-term field experiment on erosion-productivity relation was set up at Heshan Farm, Heilongjiang Province in 2005 based on comprehensive effects of erosion and tillage on soil profile. The experiment was a two-factor completely randomized block design with simulated erosion depth (8 levels of 0, 10, 20, 30, 40, 50, 60, and 70 cm)and fertilization (no fertilization and fertilization), totaling 16 treatments with 3 replications per treatment. In 2022, a series of soil physicochemical properties [bulk density (BD), soil water content (SWC), clay content, pH, soil organic C(SOC), alkali-hydrolyzed N(AN), Olsen-P(AP) and available K(AK)] and biological properties [microbial biomass C and N(MBC, MBN), catalase, urease, β-glucosidase, cellulase activity] in 0-20 cm soil layer and corn yield were measured after 18 years of the setup. 【Result】 1) Soil clay content, SOC, AN, AP, MBC and cellulase activities decreased significantly with the increase of simulated erosion depth, while soil BD and AK increased significantly. Also, fertilization significantly decreased soil BD, pH, AK, and catalase activity, but increased clay content, SOC, AN, AP, and the activities of urease, β-glucosidase, and cellulase. Interestingly, fertilization weakened the correlation between soil urease activity, BD and other physicochemical properties. 2) Simulated erosion resulted in significant reductions in soil quality and corn yield, the decrease mainly occurred before the erosion depth of 40 cm. Soil quality index decreased by 28.1% for the unfertilized treatment and 26.7% for the fertilized treatment, and yield loss was 45.8% for the unfertilized treatment and 11.7% for the fertilized treatment at 40 cm of erosion depth. Additionally, fertilization increased the soil quality index by 7.0% and corn yield by 3.0 fold. 3) The main factors affecting soil quality under simulated erosion were cellulase activity, MBC and AN for the unfertilized treatment, and cellulase activity, MBC, AP for the fertilized treatment. Also, the main factors affecting corn yield under long-term simulated erosion were AN for the unfertilized treatment and AP for the fertilized treatment. 【Conclusion】 These results quantified the degree of soil erosion on soil quality and productivity and clarified the major factors affecting soil quality and productivity in black soil, and can serve as reference for the restoration of degraded black soil.

Abstract:【Objective】 The soil carbon-to-nitrogen ratio (C/N) reflects not only soil quality but also the nutrient balance of soil carbon and nitrogen elements. Thus, rapid and accurate determination of this ratio and the grade is crucial for guiding real-time scientific fertilization and improvement of soil quality. 【Method】 This study used visible-near infrared (VNIR) and mid-infrared (MIR) spectroscopic data, along with total organic carbon (TOC), total nitrogen (TN), and C/N data from 501 typical tobacco-corn rotation farmland topsoil samples(0～20 cm) in Guizhou Province for characterization. After processing the spectra with Savitzky-Golay (SG) smoothing and standard normalization, three modeling methods were applied: partial least squares regression (PLSR), random forest (RF), and Cubist. Models for predicting soil C/N were constructed using both direct prediction of C/N and indirect prediction (first predicting TOC and TN, then calculating C/N), and the precision of C/N value and grade predictions was analyzed. 【Result】 The results revealed that: (1) For C/N value prediction, the optimal prediction strategy was direct prediction using MIR-PLSR, which had a prediction precision(relative standard error, RPD) of 1.20; (2) C/N grade could be accurately predicted, with the optimal strategy being direct prediction using the MIR-PLSR model, achieving a grade determination accuracy of 0.71; (3) The main reasons for the low prediction accuracy of C/N values are twofold. First, the uniform stringent fertilization measures in the tobacco fields have reduced the spatial variation in the carbon and nitrogen content of the plow layer soil, thereby also reducing the spatial variation of C/N(the coefficient of variation is 17.15%, indicating moderate variation). Second, the correlation between C/N and both VNIR and MIR spectra was relatively low. 【Conclusion】 Therefore, the MIR-PLSR model can be used for direct prediction of C/N grades.

Abstract:【Objective】 Soil organic carbon(SOC) is an essential indicator of soil health. It not only provides a carbon source for plant growth and maintains the physical structure of soil, but also releases carbon into the atmosphere in the form of greenhouse gases, such as carbon dioxide. Therefore, it plays a critical role in the global carbon balance. Currently, the world is experiencing climate change characterized predominantly by warming and increasing frequency and intensity of extreme weather events. However, the impacts of the changing climate, including long-term warming and extreme weather events on SOC are not entirely the same. Distinguishing and quantifying the effects of extremely high temperatures (EH) and long-term warming(LW) on SOC is the key to formulating adaptive strategies. 【Method】 In this study, we focused on paddy soils in Zhangzhou of Fujian Province, a typical subtropical region of China. Based on a 1: 50, 000 detailed soil database, we employed the biogeochemical process model (DeNitrification-DeComposition, DNDC) to simulate SOC dynamics under four climate scenarios: de-trended climate base state (CTRL), extreme high temperatures (EXP_EH), long-term warming (EXP_LW), and measured temperatures (EXP_obs). 【Result】 The results revealed that the total amount of carbon sequestered by paddy fields in Zhangzhou from 1980 to 2016 under the four different climate scenarios (CTRL, EXP_EH, EXP_LW, and EXP_obs) was 1, 032.17, 952.15, 1, 045.98 and 966.03 Gg, with the corresponding average annual sequestration rates of 93.98, 86.70, 95.24, and 87.96 kg·hm^-2, respectively. The long-term warming led to a net increase of 13.81 Gg of SOC in paddy fields across Zhangzhou, while extremely high temperatures resulted in a net decrease of 80.02 Gg. The combined effect of these two factors was -66.14 Gg in SOC, indicating that long-term warming promoted the sequestration of organic carbon in paddy soils, while extremely high temperatures reduced the soil carbon sink capacity, with extremely high temperatures exerting a dominant negative effect. Also, the variations in annual carbon sequestration rates between different climate scenarios indicated that extremely high temperatures throughout the years from 1980 to 2016 had a negative effect on carbon sequestration in the paddy soils of Zhangzhou, but the long-term warming effect on SOC turned from positive to negative around the year of 2000. This may be related to the diminishing effect of warming on plant growth over time. At the county level, climate change had the greatest impact on the carbon sequestration of Nanjing County. Additionally, the extremely high temperatures and long-term warming caused -26.23% and 7.27% impacts on its carbon sequestration rate, respectively. Furthermore, among different terrain and topographical areas, the carbon sequestration rate of hilly and mountainous areas was significantly affected by extremely high temperatures and long-term warming, with -8.84% and 1.98% changes, respectively. 【Conclusion】 In conclusion, while the paddy soils in Zhangzhou still maintain a strong carbon sequestration capacity in the context of climate change, the increasing extreme high-temperature events in the future may potentially contribute to greater carbon losses to some extent.

Abstract:【Objective】 Soil organic carbon (SOC) plays an important role in the global carbon cycle, and extremely small changes in SOC could cause dramatic changes in atmospheric CO₂ concentration. Accurately grasping the spatial distribution characteristics of SOC and its main controlling factors is an important requirement for improving soil carbon sequestration potential and coping with climate change. Therefore, this study aimed to analyze the spatial distribution of SOC in the topsoil layer (A genetic horizon), subsoil layer (B genetic horizon), and parent material layer(Parent material)in Anhui Province from the perspective of the soil profile occurrence layer and explore the factors controlling the changes of SOC in different profile occurrence layers. 【Method】 In this study, a total of 451 sites were distributed in the study area using the systematic distribution method combined with the judgmental distribution method. The basic soil parameters, such as SOC content, pH, soil texture, and bulk density, were obtained from 451 sites through wild sampling and indoor experiments. Meanwhile, the related environmental variables, such as climatic factors, topographic factors, and normalized difference vegetation index, were also collected. Also, we used geostatistical methods to obtain the best half-variance function model and spatial distribution characteristics of SOC content at different soil profile levels, as well as correlation analysis and random forest regression analysis to explore the influencing factors of spatial differences in SOC content. 【Result】 The results showed that the average organic carbon content of the soil profile in Anhui Province was 8.47 g·kg^-1 and there was a phenomenon of surface aggregation of SOC, whose occurrence in the layer was as follows: A genetic horizon: 15.86 g·kg^-1＞ B genetic horizon: 5.80 g·kg^-1＞ Parent material: 3.74 g·kg^-1 and all of them had moderate spatial variability. The spatial distribution map of SOC showed that the spatial distribution of organic carbon content in each occurrence layer was generally increasing from north to south. We also found that there were some differences in the driving factors of SOC content in different profiles of the occurrence layer. In the A genetic horizon, soil texture, and bulk density were the most important factors affecting SOC content; as the depth of the soil layer increased, the influence of topographic factors and soil texture gradually strengthened on the accumulation of SOC content in the B genetic horizon. For the Parent material, the influence of soil texture, topographic factors, and bulk density were all more influential on the SOC content. 【Conclusion】 Soil texture is the main factor driving the spatial distribution characteristics of SOC in Anhui Province, but the effects of topographic factors and bulk density should also be fully considered in the subsequent development of SOC control measures, to provide theoretical support for improving soil quality and coping with climate change.

Abstract:【Objective】 It is an essential prerequisite to understanding the environmental behavior of straw carbon in farmland soil to understand the decomposition characteristics of crop straw and the properties of dissolved organic matter (DOM) released. However, the information on straw decomposition characteristics obtained from relevant studies needs to be more comprehensive and requires further investigation. 【Method】 In this study, the straws of corn, wheat, soybean, and rape were laboratory incubated for 69 days. The two-dimensional correlation-Fourier transform infrared spectroscopy (2D-COS-FTIR), ultraviolet-visible spectroscopy (UV-Vis), three-dimensional excitation-emission-matrix spectra (3D-EEM), and parallel factor analysis (PARAFAC) were employed to monitor the changes in the components of straw during decomposition (0-69 days), as well as the humification characteristics of their released DOM. 【Result】 The results showed a double increase in corn, wheat, and corn straws during their decomposition period, and all four straws reached maturity at 65-69 d. At the end of decomposition, the mass loss rates of the four straws were 56.8 %(rape), 51.1 %(corn), 48.5 %(soybean), and 44.0 %(wheat), respectively. Although the decomposition order of different substances differed in the four straws, the decomposing intensity of functional groups on the surface of the corn, wheat, and rape straw exhibited the same order (C=O > O-H > -CH₂ > -COO^-) but the soybean straw showed a different order. The dissolved organic carbon (DOC) content released by the corn, wheat, soybean, and rape straws gradually decreased and was stable at 69 days of decomposition, of which the DOC content was 23.6, 12.2, 17.2, and 10.7 mg·g^-1 biomass, respectively. During the decomposition, the SUVA₂₅₄ value and aromaticity of DOM released from decomposed corn and soybean straws gradually increased, and the E₂/E₃ value gradually decreased. In contrast, those in wheat and rape straws showed a fluctuating trend. At the end of the decomposition, the aromaticity of DOM released from decomposed corn, wheat, soybean, and rape straw was 20.58, 10.55, 17.45, and 8.32, as well as the E₂/E₃ value being 3.27, 4.29, 3.16, and 5.77. In addition, the aromaticity of maize and soybean straw DOM was higher than that of wheat and rape straw, and the E₂/E₃ value showed the opposite trend. The 3D-EEM results showed that though the DOM composition in the four crop straws varied, a similar conversion was observed from protein-like substances (I + II) to humic-like and fulvic-like substances (III + V). Four fluorescence components in the straw DOM identified by the parallel factor analysis model showed similar results. Finally, the humic-like substances (C2 and C4) comprised 35.0%-41.9%, and the fulvic-like substances (C1) accounted for 19.9%-42.9%. In contrast, the protein-like substances(C3) only accounted for 10.0%-29.4%. 【Conclusion】 Our study revealed that the decomposition of straw and the content of its released DOM were influenced by the type of crop, while the substance degradation strength and transformation pattern remained consistent.

Abstract:【Objective】 To understand the effects of land use type change on soil N cycle and eco-environment, this study aimed to elucidate the gross N transformation rates in soils under different land use types. 【Method】 A laboratory incubation experiment was conducted using a ¹⁵N labeled technique and the numerical FLUAZ model to study the difference of gross N transformation rates among soils under different land use types such as wetland, dryland, vegetable land, and forest land in the Caohai nature reserve located in the Yunnan-Guizhou Plateau. 【Result】 The results showed that land use type significantly affected gross N transformation rates in the soils. Wetland soil had the highest rates of gross N mineralization (11.95 mg·kg^-1·d^-1) and immobilization (6.13 mg·kg^-1·d^-1) while the forest soil had the lowest gross N mineralization rate (2.39 mg·kg^-1·d^-1), but the gross N immobilization rate (2.09 mg·kg^-1·d^-1) was comparable to that of dryland soil and vegetable soil (2.29 and 1.52 mg·kg^-1·d^-1, respectively). The gross nitrification rate of forest soil (0.77 mg·kg^-1·d^-1) was significantly lower than that of wetland soil, dryland soil, and vegetable soil(2.68, 6.33 and 5.39 mg·kg^-1·d^-1, respectively). The ratios of gross nitrification to NH₄⁺ immobilization and gross N mineralization to the immobilization of dryland soil and vegetable soil were both >1, whereas the ratio of gross nitrification to NH₄⁺ immobilization rate was <1 in wetland soil and forest soil, and the ratio of gross N mineralization to the immobilization rate was close to 1 in forest soil. The gross N mineralization rate was significantly positively correlated with soil organic carbon (SOC), total nitrogen (TN), C/N ratio, and soil pH, and significantly negatively correlated with silt content. Also, the gross N immobilization rate and ammonium immobilization rate were significantly positively correlated with SOC, TN, water-soluble organic C(SOC_w), and soil pH, and significantly negatively correlated with silt content. The gross nitrification rate was significantly negatively correlated with SOC_w and clay content and significantly positively correlated with sand content. 【Conclusion】 The results indicate that in comparison with the wetland soil, dryland soil, and vegetable soil, the mineralization and immobilization processes in forest soil were more tightly coupled, thereby decreasing the occurrence of nitrification and subsequent NO₃^- loss to the environment. The results of this study can provide a scientific basis for the rational layout of land use and the evaluation of the environmental effects of ecological restoration projects within the Caohai Nature Reserve.

Abstract:【Objective】 Food waste composting is one of the potential directions of food waste resource utilization. Food waste compost is rich in organic matter and salt, and its impact on soil aggregates is still unclear. Exploring the influence of food waste compost application on the stability of paddy soil aggregates and its mechanism can provide references for agricultural utilization of food waste compost. 【Method】 Six treatments were set up in this study: No fertilizer (CK), Chemical fertilizer (F), Food waste fresh compost (FC), Food waste aged compost (AC), Chicken manure organic fertilizer (CM), Pig manure organic fertilizer(PM), The effects of these treatments and the influence of food waste compost on the stability of soil aggregates and soil surface electrochemical parameters were investigated. Correlation analysis and redundancy analysis (RDA) were used to investigate the main factors affecting the stability of aggregates. 【Result】 The results showed that: (1) Food waste compost enhanced the water stability of paddy soil aggregates, and reduced the slaking and differential swelling effects. Also, the MWD_Yoder, MWD_LB-fast,and MWD_LB-slow of AC were 21.4%, 107.8%, and 49.3% higher than CK, respectively. (2) The electrochemical properties of the soil surface were the main factors affecting the stability of aggregates and the surface charge density of the four organic fertilizers increased by 29.0%-45.2%. (3) Organic matter has a significant correlation with surface charge density, specific surface area, and surface charge number, and the correlation coefficients are 0.67, 0.53, and -0.63, respectively. Furthermore, exchangeable calcium showed a significant positive correlation with organic matter and the correlation coefficient was 0.90. 【Conclusion】 Food waste compost can enhance the surface charge density of soil by increasing soil organic matter, thus increasing the cementation between exchangeable calcium and soil particles and enhancing the stability of soil aggregates.

Abstract:Pinus sylvestris var. mongholica is one of the major vegetation restoration trees in the northern sand-prevention belt of China, which plays a vital role in the sheltering of wind and sand fixation, regulating regional microclimate, and maintaining ecosystem stability. 【Objective】 This study seeks to clarify the dynamics and controlling factors of transpiration in P. sylvestris plantations in water-limited sandy regions and provide a scientific basis for the reasonable construction and sustainable management of artificial plants. 【Method】 This study used the thermal dissipation probes, soil moisture sensor, automatic weather station, and groundwater level monitor to continuously observe the sap flow density, soil moisture content, meteorological parameters, and groundwater level in the sandy region of Yulin City, northern Shaanxi Province. With this design, we aimed to reveal the characteristics and controlling factors of transpiration water consumption of P. sylvestris. 【Result】 Results showed that: (1) The sap flow density of P. sylvestris increased initially and then decreased during the monitored period (May 2021 to October 2021). On a sunny day, the sap flow density displayed an unimodal curve and had a relatively high peak value; however, on cloudy and rainy days, the sap flow density varied irregularly and had relatively low peak values. (2) The sap flow density was most sensitive to the changes in wind speed and air temperature, followed by groundwater level fluctuation. (3) The average daily transpiration rate of P. sylvestris was 0.67 mm·d^-1, and the total transpiration water consumption in the growing season was 147 mm. 【Discussion】 The seasonal variations of meteorological parameters (vapour pressure deficiency, wind speed, air temperture, photosynthetically active radiation) and groundwater level and the associated changes in soil water content were the main factors controlling the dynamics of transpiration water consumption of P. sylvestris. The study results can provide theoretical guidance for high efficient use of water resources and sustainable management of sand-fixing plants in the sandy region.

Abstract:【Objective】 A variety of dissolved organic matter (DOM) and microorganisms affect mercury transformation under anaerobic conditions by mediating biogeochemical cycles. However, it is still unclear how specific organic matter would affect mercury transformation under this condition. 【Method】 Using batch experiments, the effect of DOM and the co-culture of microorganisms on mercury transformation were investigated. Under simulated the anaerobic environment, three kinds of DOM(cysteine and glutathione containing sulfhydryl and fulvic acid) and two kinds of bacteria (Shewanella putrefaciens CN32 and Geobacter sulfurreducens PCA) were selected to create a reduction environment and methylated mercury, respectively. Batch experiments were carried out to investigate the effect of DOM and the co-culture of microorganisms on mercury transformation. 【Result】 The results showed that the unit cell adsorption/uptake capacity of G. sulfurreducens PCA for Hg(Ⅱ) was 69.0% of that of S. putrefaciens CN32. Cysteine and glutathione did not alter the proportion of intracellular mercury in G. sulfurreducens PCA, but the proportion of intracellular mercury in S. putrefaciens CN32 was decreased. In the culture of G. sulfurreducens PCA, cysteine promoted mercury reduction and methylation, glutathione promoted mercury reduction, and fulvic acid inhibited mercury reduction and methylation. In the co-culture system of S. putrefaciens CN32 and G. sulfurreducens PCA, the mercury methylation ratio was as high as 18.7%±3.1% after the addition of cysteine complexed mercury, which was mainly attributed to the enhancement of Hg methylation of G. sulfurreducens PCA by microbial co-culture. 【Conclusion】 The results of this study elucidate the mechanism of DOM and co-culture of microorganisms on mercury species transformation in anaerobic condition, and provide a theoretical basis for the remediation of mercury pollution in flooded paddy field wetland.

Abstract:【Objective】 The reductive release of arsenic (As) from paddy soils can be enhanced under waterlogged conditions. This study aimed to investigate the mechanisms of Mn-modified biochar (MBC), with high oxidation and adsorption capacity, on inhibiting As release in the waterlogged paddy soil microcosms and to reveal the potential pathways of mediating As transformation and speciation in soil solution and soil. 【Method】 This study determined changes in the basic properties of soil solution, soil, and biochar through mixed or separate incubation of biochar and flooded soil. 【Result】 The results showed that, compared with the control and unmodified biochar, MBC significantly promoted the oxidation of As (III) to As(V) in the soil solution, keeping a low concentration of As(III) (0.02-0.88 mg·L^-1) throughout the incubation period. The Mn released from MBC into the soil solution was readily precipitated with As(V). Also, the MBC containing rich pore structure and oxygen-containing functional groups would promote its adsorption for more inorganic arsenic (iAs). MBC showed greater affinity for Fe (3.12 mg·g^-1 of Fe was adsorbed on MBC after 28 d), leading to a significant decrease of Fe concentrations in the soil solution (P < 0.05) and enhanced the adsorption of iAs on the solid-phase. The reduction of Mn-oxides on MBC increased the pH (0.08-0.22 pH units) of the soil solution, which further promoted the precipitation of Fe on the solid phase thereby strengthening its adsorption for iAs. As a result, the concentration of iAs extracted from the MBC was 12 times higher than that of the unmodified biochar after incubation of 28 d. The high oxidative properties of MBC inhibited the reductive dissolution of Fe minerals, thereby significantly reducing the soil-available Fe and As concentrations (P < 0.05). This led to the transformation of soil available As to iron-manganese bound and residual fraction As. As a result, the soil available As was stabilized under a lower range of concentrations. 【Conclusion】 Generally, the addition of MBC to waterlogged paddy soil can inhibit the release of iAs from the solid phase and promote the transformation of mobile iAs into more stable forms in the soil, resulting in a significant reduction in arsenic mobility and toxicity in waterlogged paddy soil.

Abstract:【Objective】 Extensive regions of purple soil are afflicted by acidification, whereas calcareous purple mudstones, distinguished by their alkaline pH, abundant mineral composition, and low heavy metal content, are theoretically well-suited to ameliorating acidic purple soil in their vicinity. 【Method】 An 80-day laboratory incubation experiment was conducted to evaluate the effectiveness of calcareous purple mudstones in ameliorating acidic purple soil. The geological ages of the two parent rocks were the Jurassic Shaximiao Formation (J₂s) and the Jurassic Suining Formation (J₃sn). 【Result】 The findings revealed that both purple mudstones effectively neutralized soil acidity, enhanced soil potassium content and, increased potassium bioavailability, and reduced the bioavailability of heavy metals. These mudstones offer a promising solution for improving acidic purple soil, thereby promoting soil health and fertility. Compared to J₂s mudstone, J₃sn mudstone exhibited a superior overall improvement effect on acidic purple soil due to its richer calcium content. (1) When J₂s mudstone was added to acidic purple soil at rates of 2%, 5%, and 10%, the soil pH increased gradually from 4.73 to 4.93, 5.30, and 6.27, respectively. Concurrently, the soil exchangeable acidity decreased from 2.84 cmol·kg^-1 to 2.79, 1.40, and 0.70 cmol·kg^-1, respectively. Differently, when J₃sn mudstone was added at the same rates, the pH of the acidic purple soil increased significantly to 7.20, 7.87, and 8.00, achieving neutral to alkaline levels. Notably, no exchangeable H⁺ or Al³⁺ was detected in the soil after the addition of J₃sn mudstone. Additionally, the addition of both mudstones resulted in an increase in soil exchangeable Ca²⁺, effective cation exchange capacity, and base saturation. (2) Overall, the addition of both J₂s and J₃sn mudstones to acidic purple soil resulted in a gradual increase in the contents of rapidly available potassium (K), slowly available K, and total K. Specifically, after an 80-day incubation period, the proportion of soil available K to total K increased from 1.58% to 1.76%, 1.88%, and 2.08% with the addition of 2%, 5%, and 10% J₂s mudstone, respectively. In comparison, the addition of J₃sn mudstone at the same rates led to a more significant increase in the proportion of available K to total K, reaching 1.91%, 2.01%, and 2.24%, respectively. (3) The addition of purple mudstones did not significantly increase the content of total heavy metals (Cu, Zn, Ni, Pb, Cd) in soil, but it significantly decreased the available heavy metal content in proportion to the total content. This reduction was more pronounced with the addition of J₃sn mudstone compared to J₂s mudstone, indicating its superior passivation effects on heavy metals in acidic purple soil. 【Conclusion】 Given the widespread availability, cost-effectiveness, ease of crushing, and convenience of application of calcareous purple rocks in regions where purple parent rocks are naturally exposed, they offer a practical solution for improving acidic purple soil. It is recommended that, under field conditions, 15～45 tons per ha of J₃sn mudstone or 75～120 tons per ha of J₂s mudstone should be applied to ameliorate acidic purple soil. By leveraging these mudstones, farmers and land managers can efficiently ameliorate acidic purple soil, thereby promoting soil health, crop yield, and overall ecosystem resilience.

Abstract:【Objective】 The safe utilization of farmland with mild to moderate cadmium (Cd) pollution is of great significance for the safety of agricultural products and human health. However, the effects of plant growth-promoting bacteria with the ability to immobilize Cd and regulate Cd-uptake by wheat plant from weakly alkaline farmland soil remains unexploited. 【Method】 Triticum aestivum L. Yangmai-13 was used as the tested plant, and weakly alkaline heavy metal polluted farmland soil was used as the test soil. Pot experiments were conducted to study the dynamic effects of Pseudomonas taiwanensis WRS8 on wheat growth, Cd content in rhizosphere soil and different parts of wheat, as well as rhizospheric and root endophytic bacterial communities during the jointing, booting, and maturity stages. 【Result】 The results showed that compared to the control group without inoculation, rhizosphere inoculation with strain WRS8 led to a significant increase in the aboveground biomass, root biomass, and grain weight of Yangmai 13 by 34% - 64%, 60% - 102%, and 10% - 14%, respectively. It decreased the Cd content in shoots, roots, grains, and rhizosphere soil by 55% - 60%, 5% - 8%, 78% - 82%, and 32% - 49%. Moreover, inoculation with strain WRS8 significantly increased the pH value of the rhizosphere soil during the booting and maturity stages. In terms of rhizospheric and root endophytic bacterial communities, inoculation with strain WRS8 only resulted in a significant reduction in the alpha diversity index of endophytic bacterial communities during the booting stage; The principal co-ordinates analysis clustering results showed that both the treatment with live and inactivated bacteria significantly changed the bacterial community structure in the rhizosphere soil and roots, and the bacterial community structure also changed significantly with the extension of the growth period. Inoculating strain WRS8 reduced the relative abundances of Chloroflexi and Proteobacteria in the rhizosphere soil, while increasing the relative abundance of Arthrobacter and Bacillus. Also, strain WRS8 inoculation reduced the relative abundances of Actinobacteria and Chloroflexi phyla of root endophytic bacterial communities, while increasing the relative abundance of Pseudomonas during the jointing and booting stages. 【Conclusion】 In summary, strain WRS8 not only significantly reduced the absorption of Cd by Yangmai 13 from weakly alkaline farmland soil, but also effectively improves wheat biomass and yield, suggesting its potential to achieve safe utilization of weakly alkaline heavy metal polluted farmland.

Abstract:【Objective】 The combustion of fossil fuels such as coal emits a large amount of particulate matter and heavy metals into the atmosphere, which are then significant sources of input into the agricultural environment by dry and wet deposition. These pollutants will directly influence crop growth and heavy metal accumulation, and indirectly threaten human health through the food chain. Atmospheric particulate matter rich in heavy metals can enter the plant through two pathways: deposition into the soil followed by root absorption or direct foliar uptake of dry deposition on the crop leaf surface. However, the respective proportions and specific mechanisms of these pathways remain elusive. 【Method】 An open-side(covered with fine particulate matter filter membranes) transparent chamber was designed for vegetable pot experiments, simulating the actual dry deposition flux of atmospheric particulate matter in diverse coal-burning regions. This quantitative study systematically compared the effects of fly ash from two representative coal-fired power plants in southern and northern China on lettuce (Lactuca sativa L.) growth and the leaf accumulation of typical heavy metals through deposition into soil and leaf surface, respectively. 【Result】 The results indicated that atmospheric deposition is a significant source of Cd, Pb, Cr, and As in crops. The heavy metal contents in lettuce leaves increased with the fly ash deposition. The proportion of deposited Cd accumulated by the edible above-ground parts of lettuce through the foliar uptake is 40.9%-84.2% and the proportion of Pb can be 62.3%-85.6%. This indicates that direct foliar uptake is the main pathway for lettuce leaf accumulation of Cd and Pb in atmospheric particulate matter, especially for metals with high content (Pb) or bioavailability (Cd) in particulates, and if the amount of particle deposition does not exceed the foliar uptake capacity. However, when the atmospheric deposition flux is high or the bioavailability is low, heavy metals such as As in particulate matter are mainly accumulated by leaves through the traditional pathway of soil-root migration, absorption, and transport. Because of the higher contents of most heavy metals and stronger bioavailability in the soil-lettuce system, the southern fly ash induced higher accumulation of heavy metals by the leaf, and stronger toxic effects translated to lower photosynthetic activity and less biomass. 【Conclusion】 Consequently, comprehensive pollution control measures such as source prevention and reduction of heavy metal deposition input from the emissions of atmospheric particulate matter like coal combustion, as well as suppression of leaf dust retention, are of great environmental and health significance for ensuring crop growth and the quality and safety of leafy vegetables in coal burning areas.

Abstract:【Objective】 Intercropping is an effective strategy for increasing soil carbon (C) sequestration by utilizing farmland biodiversity. The aim of this study was to investigate the contribution of peanut rhizosphere microbes adjacent to maize to soil organic C (SOC) sequestration in an intercropping system. 【Method】 Based on the long-term peanut/maize intercropping experimental platform of Jiangsu Academy of Agricultural Sciences, two rows of peanuts and two rows of maize were planted in strips. Ecological test plate (BIOLOG) and gas chromatography were used to analyze the C metabolic ability of maize to adjacent peanuts rhizosphere microbes and the accumulation of microbial necromass C. 【Result】 The results showed that compared with peanuts planted far away from maize, peanuts planted adjacent to the maize decreased rhizosphere polyphenol oxidase activity by 19.0%, soil respiration rate by 18.2%, average color change rate (AWCD) by 22%, rhizosphere microbial metabolism of phenolic acids and amino acids by 149.4% and 16.1%, respectively. The total amino sugar ( TAS ) content of peanut rhizosphere soil adjacent to maize was 6.45% higher than that of peanut planted far away from maize, and the content of bacterial necromass C and fungal necromass C was increased, which eventually led to a 12.9% increase in SOC. 【Conclusion】 Our study suggests that adjacent maize does not change the soil respiration rate of the peanut rhizosphere, but reduces the activity of SOC decompositiong enzymes in the peanut rhizosphere and enhances the ability of rhizosphere microbes to metabolize a wider range of organic carbon components, thereby increasing SOC by accumulating bacterial and fungal necromass C.

Abstract:【Objective】 Soil salinization restricts the improvement of nutrient utilization efficiency and productivity enhancement. Studying the dynamics of soil nutrient changes and microbial feedback under saline stress can provide a scientific basis for nutrient management in salt-affected soils. 【Method】 Soils with salinity ranging from <3 g·kg^-1(S₁), 3～10 g·kg^-1(S₂), and >10 g·kg^-1(S₃) of typical soil salinization areas in China were collected. By analyzing the differences in carbon, nitrogen, and phosphorus contents, microbial biomass, extracellular enzyme activity and their ecological stoichiometric ratios, this study aimed to clarify the changing trend of soil nutrients and microbial metabolism limitation characteristics under different salinity barriers. 【Result】 The results of the study showed that: (1) Organic carbon, total nitrogen, total phosphorus, alkaline dissolved nitrogen, and available phosphorus contents of the salt-affected soils all decreased. According to the nutrient grading standards of the Second National Soil Census, the organic carbon, total nitrogen, and alkaline dissolved nitrogen of S₃ all dropped to the fifth level (deficiency), while soil phosphorus and potassium pools were all relatively sufficient. (2) The ratio of extracellular carbon-acquiring enzyme activity to extracellular nitrogen-acquiring enzyme activity (Enzyme C/N), the ratio of extracellular carbon-acquiring enzyme activity to extracellular phosphorus-acquiring enzyme activity (Enzyme C/P) and the ratio of extracellular nitrogen-acquiring enzyme activity to extracellular phosphorus-acquiring enzyme activity (Enzyme N/P) of different salt-affected soils all deviated from 1: 1 to different degrees. Also, the results of vector characteristics of extracellular enzyme stoichiometry showed that microbial carbon limitation and microbial nitrogen limitation in S₃ were significantly higher than those in S₁ and S₂. This phenomenon indicates that increased salinization caused soil elements and microbial metabolic activity to gravitate towards carbon and nitrogen resource limitation. (3) The salt content (TS), Na⁺, K⁺, exchangeable sodium percentage (ESP), Cl^-and annual average evaporation-precipitation ratio(MAV/MAP)were the key constraints on changes in the carbon, nitrogen, and phosphorus stoichiometric ratios of soil nutrients, microbial biomass, and extracellular enzyme activities in salt-affected soils. The results of the random forest model showed that Cl^-, TS, and MAV/MAP were the main drivers of microbial relative carbon limitation. TS, ESP, sodium adsorption ratio(SAR), Cl^-, Na⁺ and MAV/MAP were the main drivers of microbial relative nitrogen limitation. 【Conclusion】 In summary, salinity barriers are more likely to lead to carbon and nitrogen limitation in arable soils than the relative abundance of phosphorus and potassium nutrient pools, and the degree of limitation increases with the strengthening of salinity barriers. Therefore, there is an urgent need to put forward methods of organic regulation and efficient carbon and nitrogen management for salt-affected arable soils.

Abstract:【Objective】 Exogenous substrate quality (carbon to nitrogen ratio, C/N) can mediate priming effect (PE). However, the effects and regulation mechanism of priming effect under different C/N ratios of substrate addition is still unclear. 【Method】 The effects and regulation mechanism of purple soil which was fertilized by crop straw with synthetic fertilizers were explored through an indoor incubation experiment using glucose and ammonium sulfate. 【Result】 Positive priming effect during the incubation period was significantly reduced by 87.4% and 93.7% when the material C/N was 10 (CN10) compared to the treatments with a C/N of 50 (CN50) and 100(CN100). CN100 and CN50 treatments significantly increased soil soluble organic carbon (DOC) and microbial carbon (MBC) content but significantly decreased total soluble nitrogen(TDN)content compared to CN10. After 14 and 43 days of incubation, CN100 treatment significantly elevated the activities of cellobiohydrolase (CBH), β-N-acetylglucosaminoglycosidase (NAG), and leucine aminopeptidase (LAP) compared to CN10. Positive PE in the first two weeks was significantly positively correlated with MBC, CBH, NAG, and LAP, and negatively correlated with TDN, (βG+CBH)/(NAG+LAP)(βG, β-glucosidase), and at the end of the incubation, the positive PE was significantly positively correlated with MBC, βG, CBH, NAG, LAP, and (βG+CBH)/(NAG+LAP) and remained negatively correlated with TDN. 【Conclusion】 Lower C/N substrate addition significantly reduced the positive PE in purple soils and contributed to efficient soil carbon sequestration; Microorganisms responded to changes in the relative effectiveness of nutrients in the soil environment mainly by adjusting the activities of key enzymes, which in turn regulated the PE. This study can provide a theoretical basis for regional development of fertilizer application programs for efficient carbon sequestration, as well as an in-depth understanding of carbon dynamics in agroecosystems and their microbial-driven mechanisms.

Abstract:【Objective】 The approach of reducing chemical fertilizer usage while increasing the application of organic amendment is a common strategy for maintaining optimal crop yields and preserving soil ecological functions. Biochar, as a carbon-rich, alkaline, and porous byproduct produced from biomass pyrolysis, has great potential in soil biodiversity restoration and soil health improvement in acidic red soil areas. 【Method】 This study conducted a 2×3 full factorial interactive design experiment in red soil cultivated with sweet potato-rapeseed in subtropical arid areas. The experiment involved the application of organic amendment (control without organic material application, straw, and biochar) and two fertilizer application rates (full dose of NPK fertilizer and reduced dose of 60% NPK fertilizer), totaling six treatments. The aim was to investigate the impact of biochar application on nematode communities in upland red soils and to understand the underlying mechanisms after five years of application. 【Result】 The results indicated that under full chemical fertilizer application, the use of biochar significantly increased the abundance of bacterivores and the ratio of microbivores to herbivores, reduced the root-to-shoot ratio of sweet potatoes and soil soluble organic carbon, and increased soil mineral nitrogen. Under reduced chemical fertilizer application, compared to the control and straw application, biochar significantly increased the abundance of total nematode, bacterivorous, herbivorous, and omnivorous predators. Simultaneously, it increased the sweet potato root biomass, root-to-shoot ratio, and soil pH but significantly decreased soil mineral nitrogen. By analyzing the relationship between soil nematode communities and plant growth as well as soil properties, it was evident that the application of biochar in combination with reduced chemical fertilizer led to a reduction in soil nutrient availability, thus nutrient limitation prompted plants to allocate more photosynthetic products below ground, resulting in increased crop root biomass and the abundance of herbivores. 【Conclusion】 This study suggests that under the background of reducing chemical fertilizer and increasing the application of organic amendment in China, soil fertilization practices combining biochar application with reduced chemical fertilizer should take into comprehensive consideration the potential adverse effects of nutrient deficiency on crop growth.

Abstract:【Objective】 Phosphorus solubilizing bacteria (PSB) is an important functional group of the soil microbial community. The changes in the abundance, composition, and diversity of the PSB community in the rhizosphere can affect soil alkaline phosphomonoesterase (ALP) activity and phosphorus (P) cycle dynamics. Here, we explored the mechanism of the abundance, composition, and diversity of the PSB community in regulating maize productivity under different organic fertilization treatments. 【Method】 In this study, we conducted a long-term field experiment with different organic fertilization treatments at the Yingtan National Agroecosystem Field Experiment Station of the Chinese Academy of Sciences in Jiangxi. The field experiment included four treatments: no manure (M0), low manure (M1), high manure (M2), and high manure with lime addition (M3). Illumina sequencing was used to investigate the abundance, composition, and diversity of the PSB community in the rhizosphere. 【Result】 Different organic fertilization treatments(M1, M2, and M3) significantly increased pH, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), abundance of PSB, ALP activity, and maize productivity compared to M0 treatment, with the highest values observed under M3 treatment. Organic fertilizer treatments affected the PSB community composition and diversity in the rhizosphere. Bradyrhizobium, Mesorhizobium, and Pseudomonas were the dominant genera in the PSB community under M2 and M3 treatments. Compared with the M0 treatment, the PSB community diversity was significantly increased under the M1 treatment. The abundance and dominant genera of the rhizosphere PSB community were mainly affected by AP. Correlation analysis and structural equation modeling revealed that AP and TP indirectly affected maize productivity by increasing the abundance and changing the relative abundance of dominant genera of PSB. 【Conclusion】 Taken together, this study elucidates the promotion mechanisms of the rhizosphere PSB community on the mineralization of soil organic phosphorus and maize productivity. Our findings provide a scientific basis for establishing better organic fertilization practices and enhancing the fertility and health of red soils.

Abstract:【Objective】 Nitrification, an important component of nitrogen cycling, has the potential to influence soil nitrogen availability. As a result, it will lead to ecological and environmental issues such as eutrophication, and greenhouse gas (nitrous oxide) emissions. The objective of this study was to explore the effect of Chinese milk vetch incorporation on the gene abundance of ammonia-oxidizing microorganisms in red paddy soil under a rice-Chinese milk vetch planting system. 【Method】 In a field experiment, five fertilization treatments were applied, including Chinese milk vetch incorporation (G), 100% chemical fertilizer (C), Chinese milk vetch incorporation + 100% chemical fertilizer (GC), and Chinese milk vetch incorporation + 20% chemical fertilizer reduction (GCT20), with a no fertilization treatment serving as the control (CK). Real-time quantitative PCR was used to determine the abundance of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and comammox Nitrospira Clade A and Clade B in each treatment. 【Result】 The results showed that Chinese milk vetch incorporation increased soil organic carbon and total nitrogen content compared with CK, while the 100% chemical fertilizer treatment showed no significant effect. There was no significant difference in AOA and Clade B abundance among all the treatments, indicating a weak response to nitrogen inputs from both chemical fertilizers and green manure. However, both the sole application of chemical fertilizer and its combination with Chinese milk vetch incorporation significantly increased the abundance of AOB and Clade A. Additionally, Chinese milk vetch incorporation alone had no significant effect on AOB and Clade A, suggesting their sensitivity to chemical fertilizer, but resistance to green manure nitrogen input. Furthermore, gene abundance of all ammonia-oxidizing microorganisms showed a similar trend across growth stages, with higher abundance observed during the mature stage followed by the booting stage and then the tillering stage. This suggests that growth stage and oxygen concentration are key factors influencing the growth of these microorganisms in paddy soils. 【Conclusion】 Growth stage is a key factor affecting the abundance of ammonia-oxidizing microorganisms in paddy soils. Additionally, Chinese milk vetch incorporation had a weaker promotion effect on AOB and Clade A abundance compared to chemical fertilizer, potentially contributing to nitrogen retention and stability in paddy soils.

Abstract:【Objective】 Microbial community plays an important role in soil ecological activities. It can regulate soil nutrient supply by changing the structure and function of the soil ecosystem. At present, the response of soil microbial community to warming and the main influencing factors are not well understood. 【Method】 This study collected 1 020 sets of data from 206 published domestic and foreign research literature and synthesized them to evaluate the effects of experimental warming on soil microbial community (microbial biomass, community diversity, and soil enzyme activity) using meta-analysis. The different responses of soil microbial communities to different magnitudes, durations and methods of warming, as well as planting habits and ecosystem types were evaluated and discussed. Also, the relationship between the response of soil microbial communities to warming treatment and environmental factors (annual mean precipitation, annual mean temperature, and mean altitude) was explored. 【Result】 It was found that experimental warming decreased the soil microbial community diversity by 6.7%, increased the activities of soil antioxidant enzymes, enzymes related to carbon (C), and nitrogen (N) conversion by 7.5%, 10.8%, and 19.7%, respectively. A high magnitude of warming (≥4℃)significantly reduced soil microbial biomass and increased the activities of soil antioxidant enzymes and enzymes related to C conversion. Low- temperature increase (≤2℃) had more significant effects on soil microbial community diversity and soil enzymes related to N and phosphorus (P) conversion. Also, long-term warming (>2 years) had significant effects on soil microbial biomass, community diversity, antioxidant enzymes and enzymes related to C conversion. The responses of enzymes related to N and P conversion to medium-term warming (0.5 to 2 years) were more significant and the response of soil microorganisms to experimental warming was different among different ecosystems. Further analysis revealed that the response of enzyme activities related to P conversion to warming was positively correlated with annual mean temperature and annual precipitation. The response of soil microbial community diversity was negatively correlated with mean annual temperature, annual precipitation and mean altitude. 【Conclusion】 In summary, the experimental warming significantly reduced the diversity of soil microbial communities while increasing soil enzyme activity. The warming amplitude, warming duration, and ecosystem type all affect the effects of experimental warming on soil microbes.

Abstract:【Objective】 Microbial communities contain a lot of rare species and play important roles in soil ecosystem functioning. However, the elevational patterns of rare microbes in soils and their effects by land-use types remain elusive for mountain ecosystems. 【Method】 In this study, soil samples were collected from farmland and forest along an elevational gradient ranging from 1 880 to 3 010 m in Laojun Mountain, Yunnan Province, China. The bacterial communities were analyzed based on high-throughput sequencing of the 16S rRNA gene. Rare species were defined based on their relative abundance and the rarity of bacterial communities was determined. The elevational patterns of rare bacterial communities and their underlying factors for the two land-use types were further explored. 【Result】 It was found that the bacterial rarity was 0.266±0.71 and 0.209±0.064 in the farmland and forest, respectively. The rarity in the farmland was significantly higher by 21.56% than in the forest and showed a significantly decreasing elevational trend. The main drivers of bacterial rarity were pH and electrical conductivity in both land-use types. The alpha diversity, such as the Chao1 index, Shannon index, and Evenness index of rare bacterial communities were significantly higher in farmland soil than in forest soil, with increases of 19.99%, 4.43%, and 0.64%, respectively. In addition, the Chao1 diversity index of rare bacteria of both land-use types, showed a significantly decreasing elevational pattern of 31.39% and 34.40%, respectively. Also, the Shannon index of rare bacteria of farmland soil showed a significant decrease of 4.93% with elevation. Compared to the forest, the rare bacterial communities in farmland had significantly higher alpha diversity and lower beta diversity, the latter of which indicates biotic homogenization. In addition, for forest soil, the relative abundance of Actinobacteria showed a significant U-shaped elevational pattern, and the relative abundance of Bacteroidota and Chloroflexi showed significant increasing and decreasing elevational patterns, respectively. However, there was no significant elevational pattern of all the dominant phyla in farmland soil. Overall, the community compositions of rare bacteria were significantly influenced by the land-use type, elevation changes, and their joint effects, where the land-use type showed the greatest effect. Rare bacterial communities in farmland and forest soils were mainly influenced by physicochemical properties such as pH, moisture, electrical conductivity, and total nitrogen, with pH having the strongest effect. Compared to farmland, the rare bacterial communities of forest showed significant relationships with more physicochemical properties and higher correlations, and thus had greater sensitivity to environmental changes. 【Conclusion】 In summary, the rare bacterial communities of both farmland and forest soils showed a significantly decreasing elevational distribution pattern in Laojun Mountain, which was mainly driven by environmental factors such as pH. The findings of this study reveal the important roles of land-use type and elevation on soil rare bacterial communities on mountainsides. These results will help to foster a deep understanding of the formation and maintenance mechanisms of soil rare bacterial communities under land-use changes and provide scientific guidance for the sustainable development of mountain ecosystem land resources.

Abstract:【Objective】 Microbes and their necromass play a key role in the accumulation and long-term sequestration of soil organic carbon (SOC). Moreover, continuous increases in nitrogen (N) and phosphorus (P) inputs can significantly affect microbe-mediated SOC accumulation processes. The microbial necromass accumulation coefficient (NAC), which quantifies the accumulation of microbial necromass per unit of microbial biomass, plays a key role in assessing the efficiency of microbial necromass accumulation. However, the influence of short-term and long-term additions of N and P on this coefficient within meadow ecosystems remains unclear. This study focused on investigating the differential responses of NAC to (1) short-term and long-term N and P additions and (2) additions of N and P across different soil layers. 【Method】 To explore the response of NAC to N and P additions, this study analyzed soil samples from the meadow on the Qinghai-Tibet Plateau subjected to 1 year (short-term)and 10 years (long-term)of N and P additions. It was measured the soil microbial necromass carbon (MNC) and the soil microbial biomass carbon (MBC), and calculated the value of NAC. Additionally, considering other environmental factors including soil physical and chemical properties, microbial extracellular enzyme activities, and plant biomass, the main influencing factors of NAC were identified. 【Result】 The results showed that after short-term N and P additions, the NAC values in the 0-10 cm and 20-30 cm soil layers were 31.33±2.97 (mean±SE) and 38.12±3.90, respectively, and N and P additions had no significant effect on NAC (P>0.05). After long-term additions of N and P, the NAC values in the 0-10 cm and 20-30 cm soil layers were 14.46±1.12 and 17.49±3.22, respectively; and the additions of N and P significantly reduced the NAC in the 20-30 cm layer (P<0.05). The results of the Random Forest indicated that pH was the most important factor affecting NAC, and the correlation analysis revealed a significant positive relationship between soil pH and NAC. Moreover, the long-term N addition, P addition and simultaneous addition of N and P significantly reduced the pH of the 20-30 cm soil layer. These findings suggest that the decrease in soil pH due to long-term N and P supplementation is the main cause of the reduction in NAC. The lowered soil pH may lead to the dissolution of minerals, thereby reducing the mineral protection of MNC, making it more susceptible to decomposition, ultimately decreasing the NAC of microorganisms. 【Conclusion】 In summary, changes in pH resulting from long-term nutrient additions dominated the changes in NAC. In the context of ongoing increases in N and P deposition, it is advisable to closely monitor changes in soil pH and implement timely measures to maintain the stability of SOC. This study explores the differential responses of NAC to N and P additions and their influencing factors, providing data support for understanding microbial-mediated carbon accumulation under the context of increasing N and P deposition.

Abstract:【Objective】 As indicators reflecting soil fertility and biological activity, the soil microbial community plays key roles in global biogeochemical cycles by participating in litter decomposition and nutrient mineralization. The soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) are labile and available nutrients for plants, and important for maintaining ecosystem functions. However, there is still a lack of information on the spatial distribution of the soil microbial biomass and the potential key drivers affecting it in the alpine meadows of Northwest Sichuan Province. Therefore, the current study aims to investigate the spatial heterogeneity of soil microbial biomass in the alpine meadows of Northwest Sichuan and its influencing factors based on the Second Comprehensive Scientific Expedition to the Qinghai-Tibet Plateau project. 【Method】 The typical alpine meadows in Northwestern Sichuan were investigated in this study to determine soil MBC, MBN and MBP by chloroform fumigation method. Soil pH, water content, total carbon, total nitrogen and total phosphorous were also measured. 【Result】 The results showed that (1) The content of MBC and MBN showed a decreasing trend from South to North alpine meadow in the Northwest Sichuan Province. Conversely, the MBP content showed an increasing trend from South to North while the MBC: MBN ratio showed a decreasing trend from Northeast to Southwest. Nevertheless, the MBC: MBP ratio was more complex and showed an overall decreasing trend from South to North while the MBN: MBP ratio showed an increasing trend from West to East.; (2) Random forest modeling results showed that mean annual temperature (MAT), mean annual precipitation (MAP), soil pH, and soil moisture (SMC) were important factors that positively affected soil microbial biomass and its stoichiometric ratio. The structural equation modeling (SEM) results further showed that soil pH and soil bulk density (BD) had direct negative effects on the changes of soil microbial carbon, nitrogen and phosphorous biomass whereas the stoichiometric ratio and soil total carbon (TC) had direct positive effects on them. MAT and MAP indirectly and negatively affected soil MBC, MBN, MBP, and the stoichiometric ratio, which was mainly attributed to the effects of MAT and MAP on soil physicochemical properties. Specifically, MAT and MAP increased both MBC and MBP mainly by lowering soil pH, and MAT also directly decreased TC, which increases MBN as well as decreased MBP; (3) Generally, the soil nutrients are limited in the alpine meadows of Northwest Sichuan Province, and showed the following trend: carbon > nitrogen > phosphorus. 【Conclusion】 Soil pH, BD, and TC had direct effects on the alteration of soil microbial biomass and its stoichiometric ratios in the alpine meadows of Northwest Sichuan Province, while MAT and MAP indirectly affected the soil microbial biomass and its stoichiometric ratios. In addition, the latitude and longitude showed effects on the spatial distribution pattern of nutrient limitation in the study area.