Abstract:Sulfur-oxidizing microorganisms are the primary agents driving the marine deposition cycle of sulfur elements. However, these microorganisms often encounter the challenge of spatial separation between their electron donors (sulfides) and electron acceptors (oxygen and nitrate) within marine deposits. A recent study has identified cable bacteria, a type of sulfur-oxidizing microbe capable of long-distance electron transport. This discovery represents a significant advancement in our understanding of the spatial separation of electron donors and acceptors in sulfur-oxidizing microorganisms. In sediment, cable bacteria transmit electrons generated by sulfide oxidation from the anaerobic layers deep within the sediment to the surface, spanning distances of several centimeters through their conductive fibers. This process facilitates the coupling of sulfide oxidation and oxygen reduction across spatial distances and induces significant pH migration, influencing the circulation of trace elements such as calcium, iron, manganese, and phosphorus within the sedimentary environment. These interactions impact the ecological environment in ways that cannot be overlooked. In light of this, the present paper consolidates current literature on cable bacteria and provides a comprehensive overview of their classification, habitats, structural and movement characteristics, long-distance electron transfer capabilities, and environmental impacts. Utilizing a bibliometric approach, the literature is clustered and visually analyzed to identify current research hotspots and future development trends concerning cable bacteria. This study aims to offer new insights and directions for further investigation into the physiological characteristics and environmental effects of cable bacteria.

Abstract:【Objective】Soil erosion is a significant cause of degradation in black soil. To make matters worse, there is little or no comprehensive evaluation of soil erosion-degradation in black soil cropland in Northeast China. Thus, clarifying the spatial differentiation characteristics of soil erosion and degradation, as well as the different soil erosion-degradation types will be conducive to the implementation of soil protection and restoration technologies tailored to local conditions.【Method】Based on the physical and chemical properties of soil samples collected during two periods of soil survey, the soil species survey in the 1980s and the soil series survey in the 2010s, a comprehensive soil quality index was constructed in this paper via principal component analysis, considering soil thickness, soil organic matter content, total nitrogen content, total phosphorus content, total potassium content, pH value, and bulk density. The spatial distribution maps of soil properties in the 1980s and 2010s were created with a 90 m resolution using environmental covariates and the random forest model. Fuzzy membership functions were built to evaluate soil quality, and soil degradation was the difference between the quality from these two periods. A total of 15 erosion-degradation types of black soil were classified based on two aspects: the intensity of soil erosion types and the degree of soil quality degradation.【Result】The results showed that about one-third of the cropland in Northeast China experienced erosion-degradation. Among them, water erosion is extensive and causes serious degradation. The most typical type was mild water erosion-serious degradation (occupying 23.7% of erosion croplands), which was distributed in the east of the Great Khingan Mountains, the north of the Lesser Khingan Mountains, the south of the Songnen Plain, and the north of the Changbai Mountains. Other types include mild water erosion-slight degradation (16.4%), severe water erosion-serious degradation (14.1%), mild water erosion-no obvious degradation (7.4%), severe water erosion-slight degradation (6.8%), and severe water erosion-no obvious degradation (3.1%). Additionally, the main type of wind erosion was severe wind erosion-slight degradation type (10.1%), which was distributed in the middle of the Songliao Plain and Horqin Sandy Land. This was followed by mild wind erosion-slight degradation (8.3%), severe wind erosion-serious degradation (3.2%), mild wind erosion-serious degradation (2.3%), mild wind erosion-no obvious degradation (1.9%), and severe wind erosion-serious degradation (1.3%). The land area of freeze-thaw erosion-degradation types was small (1.4%), having mild intensity and concentrated in the western foothills of the Great Khingan Mountains.【Conclusion】Overall, our study reveals that the higher the quality of black soil, the more likely it is to suffer serious degradation, which is greatly influenced by severe erosion. Also, the degradation caused by water erosion was the most serious. According to the different spatial distribution of erosion-degradation types, distinct black soil protection and sustainable utilization technologies should be promoted.

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

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

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

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

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

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

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

Abstract:【Objective】Normal alkanes (n-alkanes) are relatively stable components of soil organic matter. Identifying the composition and occurrence mechanisms of n-alkanes in black soil is of great significance, as it can reveal the source of organic matter and the changes in the soil-forming environment. The purpose of this study was to evaluate the influence of soil-forming processes on the n-alkane index of black soil and to explore the indicative significance of n-alkanes in black soil.【Method】In this study, samples from three typical soil formation processes of Isohumosols in the Songnen Plain were collected, including the HL profile naturally developed under relatively stable terrain conditions, the YA profile affected by erosion and accumulation under unstable terrain conditions and the SH profile with evident animal disturbance processes. The ultrasonic extraction method was utilized to extract free n-alkanes from the soil. The distribution characteristics and compound-specific carbon isotopes were analyzed. 【Result】The results showed that the HL and YA profiles were unimodal, with the main peak being C₃₁ and the odd-even predominance, while the SH profiles were bimodal, with the main peak being C₂₃ and C₃₁. The ∑C_25～35 and CPI values of HL and SH sections decreased with the depth of the section, while the ∑C_25～35 and CPI values of the YA section increased in the buried layer. The mean δ¹³C_alk values of HL and YA profiles ranged from –29.30 to –30.27‰ and –29.79 to –32.60‰, respectively. Our results indicate that the buried layer is found to enhance the retention of n-alkanes, while disturbance may disrupt other indicators of n-alkanes in situ records. Furthermore, the analysis of n-alkanes and their carbon isotopes suggests that soil organic matter primarily originates from terrestrial higher plants, particularly C3 plants. Since the Holocene period, herbaceous plants dominate the black soil area of the Songnen Plain, with the proportion of woody plants gradually increasing during the development of black soil. Combining the data from ¹⁴C dating, it is inferred that the climatic conditions during the last deglaciation likely played a role in the initial development of black soil, while the warm and wet climate of the Middle Holocene contributed to the maturity of black soil.【Conclusion】These results confirm that n-alkanes in black soil can reflect the impact of soil erosion-deposition and disturbance on n-alkanes. Thus, this study will provide a basis for revealing the changes in organic matter sources during the formation of black soil and reflect the soil-forming environment of black soil.

Abstract:【Objective】Paddy soil is a type of anthropogenic soil formed through long-term water cultivation and ripening, which has a high organic carbon storage and carbon sequestration potential. Clarifying the protection mechanisms of organic carbon in paddy soil can provide a theoretical basis for carbon sequestration, emission reduction, and sustainable utilization of paddy soil. 【Method】Using a 1 000-year chronosequence of paddy soils formed through coastal reclamation in Eastern China, the distribution characteristics and evolution patterns of occluded/free and particulate/mineral-bound organic carbon were investigated within soil aggregates under long-term rice cultivation. This was achieved through methods such as force-stable aggregate fractionation and physical particle/density grouping. 【Result】While soil organic carbon (SOC) gradually accumulated under long-term rice cultivation, the contents of particulate organic carbon (POC) and mineral-bound organic carbon (MOC) also increased. However, MOC was the dominant form, accounting for 64.4% – 87.9% of the total SOC pool. The distribution patterns of different size soil aggregates were consistent, with macroaggregates (74.0% – 77.6%) being the most abundant, followed by microaggregates (9.2% – 15.9%) and silt and clay-sized microaggregates (8.6% – 15.7%). Therefore, over 70% of SOC was stored in the macroaggregates. The organic carbon content of aggregates of all particle sizes increased with the increase of paddy cultivation age and grain size. Among different types of soil aggregates, mineral-bound organic carbon (MOC) was the dominant form. In macroaggregates, occluded microaggregates, and free microaggregates, the MOC contents were up to 2.9, 1.1, and 3.2 times higher than POC, respectively. The protective effect of occluded microaggregates on POC was stronger than free microaggregates, with the POC content in occluded microaggregates being up to 1.5 times higher than in free microaggregates. 【Conclusion】Long-term rice cultivation is beneficial for SOC sequestration under the physical protection of soil aggregates. The protective effect of occluded microaggregates on POC is a potential mechanism for carbon sequestration in paddy soil.

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

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

Abstract:【Objective】Neonicotinoid pesticides are one of the most commonly used insecticides in citrus orchards in the hilly areas of southern China. The long-term fertilization of orchards can alter the content and structure of soil organic matter, which in turn affects the adsorption behavior of pesticides in the soil. Therefore, gaining an in-depth understanding of the adsorption behavior of a typical neonicotinoid pesticide (imidacloprid) on soil humus in orchards is crucial for improving our knowledge of the environmental behavior of this class of pesticides in soil. This will provide a theoretical basis for preventing and controlling pesticide surface pollution at its source.【Method】Humic acid (HA) fractions (F₁to F₁₀), low carbon humin (HuL) and high carbon humin (HuH) were extracted from soils (0～20 cm) with different cultivation chronosequences (10, 30 and 50 years). Adsorption isotherm experiments of imidacloprid on these humic fractions were conducted. 【Result】The adsorption isotherms of imidacloprid by humic acid (HA) fractions (F₁～F₁₀), and HuL and HuH fractions all fit the Freundlich model well, with R² greater than 0.9. The adsorption affinity of humic acid for imidacloprid is about 100 times higher than that of HuL and HuH. The K_d values of imidacloprid ranged from 523.1 to 5 276 L·kg^–1, 543.3 to 5 717 L·kg^–1, and 520.2 to 5 980 L·kg^–1 at C_e of 0.5, 2.0, and 3.0 mg·L^–1, respectively. All of them increased slightly with the increase of planting years. The K_OC values of imidacloprid were positively correlated with aromatic C and negatively correlated with alkyl C of HA fractions (F₁～F₁₀). Also, the carbonyl C and carboxyl C of HuL were the key carbon functional groups controlling imidacloprid adsorption, while the alkyl C of HuH was the key carbon functional group controlling imidacloprid adsorption. 【Conclusion】Therefore, long-term cultivation can improve the adsorption of imidacloprid by humic substances to a certain extent, and the aromatic carbon structure of humic acid is the key structure regulating the adsorption of imidacloprid while the aliphatic carbon structure of humin is the key structure regulating the adsorption of imidacloprid.

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

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

Abstract:【Objective】 This study aimed to explore the variations of the increased methane (CH₄) emissions and its mechanisms in paddy fields with straw incorporation across 11 consecutive years, so as to provide a scientific basis for the accurate assessment of CH₄ emissions under long-term straw incorporation.【Method】A typical double-cropping rice field in the subtropical region was selected as the research subject, and the fertilizer only treatment (CON), low amount of straw incorporation treatment (3.0 t·hm^–2, LS) and high amount of straw incorporation treatment (6.0 t·hm^–2, HS) were set up. The field experiment was conducted for 11 years (2012—2022) with CH₄ fluxes and related soil and environmental factors measured in the early and late rice seasons across the 11 years.【Result】The results showed that in the 11^th year of straw incorporation, CH₄ emissions in both the LS and HS treatments were substantially higher than those in the CON treatment, with the highest emissions recorded in the HS treatment, followed by the LS and then the CON treatment (HS > LS > CON). However, it was noted that the increment in CH₄ emissions due to straw incorporation in the 11^th year had diminished by 75.1% and 83.5% when compared to the increment in the first year (P < 0.05). In the 11^th year, the contents of soil organic carbon (SOC), ammonium nitrogen (NH₄⁺-N), and dissolved organic carbon (DOC) in the LS and HS treatments showed significant increases by 7.90% and 20.8% (LS and HS treatments, the same as below), and 15.0% and 25.7%, 19.5%, and 31.3%, respectively, compared to the CON treatment (P < 0.05). However, the redox potential (Eh) and soil bulk density (BD) exhibited significant reductions of 14.1% and 21.7%, and 10.3% and 7.76%, respectively (P < 0.05). Furthermore, the abundance of the mcrA and pmoA genes, which are instrumental in methanogenesis and methane oxidation processes, respectively, as well as the mcrA/pmoA gene ratio, were significantly enhanced in the LS and HS treatments compared to the CON, which increased by 96.0% and 152%, 12.7% and 34.8%, and 73.9% and 85.8%, respectively(P < 0.05). Through redundancy analysis, it was determined that in the 11^th year of straw incorporation, CH₄ emissions in the paddy field displayed a significant positive correlation with the abundance of mcrA and the mcrA/pmoA ratio in the soil (P < 0.05). The decrease in BD and the rise in Eh, induced by the increase in SOC content, likely fostered the augmentation in pmoA gene abundance, which might be the principal reason for the undermined increase in CH₄emissions for the straw treatments observed in the later stages of the experiment.【Conclusion】 In the subtropical regions, relative to CON, the increases in CH₄ emissions under long-term straw incorporation was reduced by approximately 80% (P < 0.05) compared to the increase under short-term straw incorporation due to the changes in SOC, BD, and Eh. Therefore, the assessment of CH₄ emissions from paddy fields with straw incorporation needs to be dynamically adjusted according to the year of duration of straw incorporation.

Abstract:【Objective】To evaluate the NO₃^–-N removal capacity of typical farmland profiles in southern China and to explore the hot moments and hot spots of denitrification.【Method】Paddy fields (rice-wheat rotation), vegetable fields, and orchards (vineyard) in the Taihu Lake region were selected for this study. Near in-situ incubation of flooded and non-flooded layers of the soil profile (0-300 cm) of these fields was performed using the Membrane Inlet Mass Spectrometer (MIMS) and Robotized continuous flow incubation system (RoFlow) over a year. 【Result】Our results showed that the soil denitrification rate exhibited distinct hot moments and hot spots across the three planting patterns. Denitrification hot moments in paddy fields were primarily observed in October during the rice season, with a rate of 17.6 nmol·g⁻¹·h⁻¹. The denitrification hot moments of vegetable fields and orchards mainly occurred in March, with rates of 44.2 nmol·g⁻¹·h⁻¹ and 45.3 nmol·g⁻¹·h⁻¹, respectively. The hot spots of denitrification in the paddy fields occurred in the topsoil (0-20 cm) with an average rate of 3.4 nmol·g⁻¹·h⁻¹. The denitrification hot spots of the vegetable fields and orchards mainly occurred at 20-100 cm, with average rates of 11.7 nmol·g⁻¹·h⁻¹ and 9.4 nmol·g⁻¹·h⁻¹, respectively. Also, the removal rate of NO₃^–-N in these denitrification hot spots exceeded 90%, and almost all NO₃^–-N in the soil profile was removed under the three planting patterns. Correlation analysis results indicated that the soil NO₃^–-N content was the primary limiting factor for denitrification. 【Conclusion】Our study reveals that the farmland soil profiles under the three planting patterns in the Taihu Lake area exhibit high denitrification rates with distinct denitrification hot moments and hot spots, effectively removing NO₃^–-N from the soil profile.

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

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

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

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

Abstract:【Objective】Bacterial wilt disease, caused by soil-borne Ralstonia solanacearum, has led to significant yield reductions or even crop failures in tomatoes, potatoes, and tobacco, severely limiting the safe supply of agricultural products. Rhizosphere microorganisms play a crucial role in mitigating soil biotic impediments. Probiotics can inhibit pathogens through antagonism or nutrient competition, while phages can target pathogens through specific infections. However, the single use of either probiotics or phages often results in unstable effects, and the high-density fermentation cost of these strains is considerable. 【Method】To establish an efficient and stable technology for reducing soil biotic impediments, this study constructed combinations of antagonistic-competitive and nutrient-competitive beneficial bacteria with phages. It explored their synergistic effects in reducing soil wilt disease through in vitro microplate and greenhouse pot experiments. The potential mechanisms of synergy between probiotics and phages were also investigated. 【Result】 The results showed that most combinations of phages and probiotics exhibited synergistic effects, significantly enhancing the inhibition of pathogenic R. solanacearum growth and the reduction of bacterial wilt disease. Notably, the combination of the antagonistic-competitive beneficial bacterium T-5 with phages resulted in an 89.19% reduction in pathogenic bacterial growth compared to the control. Greenhouse experiments indicated that the synergistic effect reduced the disease index by an average of 58.18%, with the combination of the nutrient-competitive beneficial bacterium WR21 and phages significantly reducing the disease index by 67.28%. Further studies revealed that even at lower concentrations of beneficial bacteria, the phage-bacteria synergy remained effective. At a concentration of 10⁴ CFU·g^–1 substrate, the combination of T-5 with phages reduced the disease index by 21.56% and the number of rhizosphere pathogenic bacteria by 19.21% compared to the application of beneficial bacteria alone, demonstrating a strong synergistic effect. Additionally, the study explored the impact of phage-beneficial bacteria combinations on the characteristics of pathogenic R. solanacearum. The results showed that the phage-nutrient-competitive beneficial bacteria combination significantly reduced the pathogen's carbon source utilization ability, with the WR21 and phage combination reducing the number of carbon sources utilized by the pathogen by 87.9%. Furthermore, under the dual stress of phages and antagonistic-competitive beneficial bacteria, the sensitivity of the pathogen to the antagonistic substances produced by T-5 increased by 64.10%. 【Conclusion】This study highlights the potential of phage-beneficial bacteria combinations in mitigating bacterial wilt disease and preliminarily elucidates the potential mechanisms behind their synergistic effects. These findings provide theoretical and technical support for the development of efficient soil biological obstacle reduction techniques.

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

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

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