Abstract:Wildfire is an important natural disturbance affecting terrestrial ecosystem carbon cycling under global change, and the increasing frequency and intensity of wildfire events are continuously reshaping the migration, transformation, and stabilization of post-fire soil organic carbon. This review focuses on the structural and interfacial mechanisms of soil organic carbon stabilization following wildfire disturbance and systematically synthesizes the roles of soil structural change, mineral interfacial reactions, and microbial processes in regulating post-fire carbon pool dynamics. Wildfire first causes rapid losses of surface soil organic carbon through high-temperature combustion and pyrolysis, while also inducing aggregate breakdown, pore structure reorganization, enhanced soil water repellency, and intensified runoff and erosion. These changes alter the exposure of organic carbon, its vertical migration within soil profiles, and its lateral redistribution from hillslopes to depositional zones. At the same time, thermally induced dehydroxylation of clay minerals, crystallization of iron and aluminum oxides, and the formation of pyrogenic mineral phases can reshape mineral surface reactivity and interfacial binding conditions. These effects do not simply increase or decrease mineral protection, but depend on fire severity, mineral composition, heating duration, and soil background conditions, thereby influencing the pathways and efficiency by which pyrogenic dissolved organic matter, pyrogenic carbon, plant-derived organic matter, and microbial necromass enter mineral protection systems. At the biological level, post-fire microbial communities undergo a successional shift from rapid reassembly to metabolic strategy transition. In the early stage, microbial activity promotes rapid turnover of labile carbon, whereas in later stages, enzymatic oxidation, metabolite release, necromass accumulation, and microbe–mineral electron transfer can drive the transformation of organic carbon from labile or mobile forms toward mineral-associated and physically protected states. Overall, the evolution of post-fire soil carbon pools is not governed by any single process but results from the combined effects of structural disturbance, erosion–deposition redistribution, mineral interfacial reconstruction, and microbial transformation. A systematic synthesis of these processes and their coupling relationships is important for improving mechanistic understanding of soil carbon stabilization under wildfire disturbance and for supporting post-fire carbon sink assessment and ecosystem management.

Abstract:This study aimed to investigate the differential responses of rhizosphere and bulk soil microbial diversity to long-term fertilization and to identify the key nutrient drivers. 【Method】 Rhizosphere and bulk soils were collected from tobacco plants under five treatments in a long-term field experiment established in 2010. The samples were collected from plots with no fertilization (CK), inorganic fertilizer alone (NPK), organic fertilizer alone (OM), combined inorganic and organic fertilization (NPKO), and inorganic fertilizer plus green manure incorporation (NPKG). Using high-throughput sequencing, soil physicochemical analyses, and functional prediction, we evaluated the effects of different fertilization treatments on the composition, diversity, and potential functions of bacterial and fungal communities in rhizosphere and bulk soils. 【Result】 The results showed that long-term fertilization significantly altered bacterial community structure in both rhizosphere and bulk soil, whereas fungal community structure responded significantly only in bulk soil. Proteobacteria, Actinobacteriota, Acidobacteriota, Ascomycota, and Basidiomycota were the dominant phyla shared by both habitats. Fertilization generally promoted the enrichment of Sphingomonas. Meanwhile, compared with CK, the relative abundance of Fusarium under NPKG increased significantly by 117.20%, whereas NPKO increased the abundance of Humicola in the rhizosphere and reduced Fusarium to the lowest level among all treatments, representing a 42.86% decrease relative to CK. Also, fertilization significantly increased soil carbon (32.32%–159.76%) and nitrogen (17.68%–229.80%) fractions. Soil pH, total nitrogen, total organic carbon, and dissolved organic carbon were the key factors driving rhizosphere bacterial succession (P < 0.05), whereas bulk soil fungal communities were mainly driven by alkali-hydrolyzable nitrogen. Fertilization enhanced the potential functions of bulk soil bacteria related to carbon and nitrogen metabolism and transmembrane transport. In addition, NPKO not only strengthened the potential of fungi to decompose complex organic substrates, but also reduced the predicted abundance of functions associated with potential rhizosphere pathogens.【Conclusion】 Bacterial and fungal communities showed clear habitat-specific responses to long-term fertilization, with their succession driven primarily by multiple nutrient factors in the rhizosphere soil and by alkaline hydrolyzable nitrogen in bulk soil. Additionally, combined organic–inorganic fertilization was more effective in coordinating nutrient turnover and maintaining rhizosphere microecological health.

Abstract:【Objective】The highly heterogeneous soil-rock structure in the karst area of Southwest China affects the soil hydrological process. Clarifying its controlling effect and driving factors on soil moisture is of great significance for understanding the regional hydrological cycle and improving the ecological governance of rock desertification. 【Method】Taking two typical lithologies (limestone and dolomite) as the research objects, this study designed 12 simulated soil tanks with different soil-rock structure. Based on soil moisture data (at 10, 20, 40, 70, and 100 cm soil depths) and meteorological monitoring data (precipitation, temperature, and humidity) from the hydrological year spanning March 2023 to February 2024, this study employs statistical analysis and fitting methods to investigate the characteristics of soil moisture variation across different soil-rock structures. It further examines how soil moisture content differences are influenced by both soil-rock structure characteristics and meteorological factors.【Result】The results showed that the fluctuation of soil moisture in different karst soil-rock structure decreased with the increase of soil depth; the soil moisture (11.07~43.21%) and coefficient of variation of each limestone soil-rock structure in the rainy period were higher than those in the dry period, the soil moisture in the 40~70 cm soil layer was the lowest while the storage in the 100 cm layer was relatively high, and the soil water storage was jointly controlled by the soil-rock ratio (negative correlation) and the thickness of the surface soil layer (positive correlation), with the fitting formula Z=-24.48X+0.88Y+100.47 (R2=0.9328) ; the soil moisture of dolomite was concentrated and lower than that of limestone, the average value in the rainy period (18.36~28.70%) was slightly higher than that in the dry period (15.10~25.53%), the coefficient of variation in the dry period was higher, and the soil water storage increased exponentially with the increase of soil thickness, with the fitting formula Z=13.85e(X/12.70)-13.26 (R2=0.9958) ; the soil water storage of limestone was significantly correlated with precipitation and relative humidity, while dolomite was only significantly correlated with relative humidity.【Conclusion】This study reveals the regulatory mechanism of lithology difference-dominated soil-rock structure on the variation characteristics and storage of karst soil moisture, clarifies that soil-rock fabric is a key factor in karst soil hydrology research, and provides data support and theoretical reference for regional eco-hydrological research and rock desertification governance.

Abstract:【Objective】The thickness of the loess layer overlying the Pisha sandstone area is crucial for regional ecological restoration; however, efficient detection methods are still lacking. Although ground-penetrating radar (GPR), owing to its rapid and non-destructive advantages, has been successfully applied in areas underlain by residual parent material, its suitability for detecting the soil–rock interface in regions covered by transported parent material (loess) has not yet been systematically validated. This study therefore aimed to evaluate the applicability of GPR for loess thickness determination in the Pisha sandstone area and to assess the performance of the Topp model in estimating the dielectric permittivity of loess in this region. 【Method】GPR was employed to measure loess thickness on three typical vegetation slopes (shrubland, arbor land, and grassland) in the Pisha sandstone area. The dielectric permittivity of loess was calibrated in situ through field excavation and pre-buried iron pipes. The measured permittivity values were compared with predictions from the Topp model to assess the model’s performance in this region, and the GPR-derived loess thicknesses were compared with actual excavation depths to evaluate the measurement accuracy of GPR. 【Result】The results showed that the measured relative dielectric permittivities of loess were 13.33, 19.57, and 13.92 for shrubland, arbor land, and grassland, respectively. The Topp model predicted loess dielectric permittivity with an accuracy ranging from 92.51% to 97.23%, showing no significant difference from the measured values. Also, the accuracy of GPR in determining loess thickness ranged from 87.16% to 97.78%, and the measured depths did not differ significantly from the actual burial depths. On all three slopes, loess thickness exhibited a clear increasing trend from the upper to the lower slope positions. The grassland had the largest average thickness (36.16 cm), while the arbor land had the smallest (19.06 cm). 【Conclusion】This study provides an efficient and accurate method for soil thickness investigation in the Pisha sandstone area and offers fundamental data support for soil and water conservation and hydrological process research in this region.

Abstract:【Objective】The molecular composition of soil organic matter (SOM) is central to understanding carbon cycling in agroecosystems. However, how the SOM molecular composition evolves under long-term different fertilization regimes remains poorly understood. This study aimed to elucidate the regulatory mechanisms of long-term fertilization on SOM molecular composition in red soil paddy fields.【Method】Based on a long-term field experiment, four treatments were selected: no fertilizer (CK), organic matter recycling (C), chemical NPK fertilizers (NPK), and chemical NPK fertilizers plus organic matter recycling (NPKC). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to analyze the molecular composition of SOM.【Result】(1) All fertilization treatments significantly increased soil organic carbon (SOC) and total nitrogen (TN) contents, while the NPK treatment specifically enhanced dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) contents. (2) CHO-type compounds dominated the SOM composition, accounting for 64.0% of all identified molecular formulas. (3) Compared with CK, fertilization, especially NPKC, significantly increased the relative abundance of lipid-like compounds, whereas CK enriched more plant-derived lignin-like compounds. (4) Different fertilization treatments altered the molecular classes of SOM. Specifically, the molecular composition of lipids, tannins, lignins, and carbohydrates differed significantly among fertilization treatments, whereas the responses of condensed aromatics and unsaturated hydrocarbons to fertilization were not significant.【Conclusion】This study demonstrates that long-term fertilization reshapes the molecular composition of SOM in red soil paddy fields primarily by regulating key components, including carbohydrates, tannins, lipids. This and lignins, provides direct molecular evidence for fertilization-induced alterations in soil organic matter composition.

Abstract:Red earth sediments, widely distributed in southern China, are important archives of Quaternary environmental evolution in the mid-low latitudes. Hematite (Hm) within these sediments is a key indicator of dry and hot paleoclimates. However, traditional chemical methods fall short for rapid and precise quantification in complex soil matrices. Diffuse reflectance spectroscopy (DRS) combined with multiple linear regression (MLR) was used to quantify Hm content under complex mineral backgrounds. Applied to the Tongling red earth profile in the lower Yangtze River, this approach reconstructed the Hm content record since the Middle Pleistocene. The results show a good correspondence between the reconstructed hematite Hm content and the redness index (a*), validating the reliability of a* as a Hm proxy from an absolute data perspective. Moreover, this quantitative result provides evidence for deciphering the magnetic depletion mechanism in vermiculated red earth and demonstrates the utility of DRS in paleoenvironmental studies of southern Chinese red earth. Thus, DRS-based quantitative inversion is an effective tool for analyzing complex multi-source sediments and improves the ability to identify multi-stage pedogenic overprinting in southern red earth.

Abstract:【Objective】??Soil salinization imposes combined stresses of high salinity and phosphorus (P) deficiency, thereby severely constraining plant growth. Puccinellia distans is a salt-tolerant halophyte; however, the response mechanisms of its rhizosphere microbiome to salt stress, particularly concerning organic P mineralization functional genes, remain poorly understood. This study aimed to clarify the response patterns of organic P mineralization functional genes in the rhizosphere of P. distans and to identify the underlying mechanisms. It is hypothesized that salt stress affects these microbial functional genes indirectly by altering soil physicochemical properties and root traits, which subsequently reshape root exudation patterns. 【Method】A controlled pot experiment was conducted using P. distans under five NaCl-induced salt stress gradients: control (0 g·kg-1), light (2 g·kg-1), moderate (4 g·kg-1), severe (6 g·kg-1), and extreme (8 g·kg-1). After 30 days of continuous salt stress, rhizosphere and bulk soil samples were collected. Metagenomic sequencing was employed to determine the relative abundances of key genes involved in organic P mineralization, including phnM, 3-Phytase, phnI, phnL, phoA, phoD, phnH, and phnW. Analysis of variance (ANOVA), Pearson correlation, random forest models, and partial least squares structural equation modeling (PLS-SEM) were used to identify the major drivers and causal pathways underlying changes in these genes under salt stress.【Result】??Salt stress significantly altered the relative abundances of phnM, 3-Phytase, phnI, phnL, and phoA genes in the rhizosphere, whereas only phoA and phnW responded significantly in bulk soil; phoD and phnH were not significantly affected. In the rhizosphere, 3-Phytase, phnI, phnL, and phoA exhibited a unimodal pattern, initially increasing and then decreasing with increasing salt stress. Under severe stress, the abundances of phnM, phnI, phnL, and phoA increased by 24.7%, 34.5%, 52.9%, and 34.7%, respectively; while 3-Phytase increased by 8.0% and 7.2% under moderate and severe stress. In bulk soil, phoA increased by 26.0% and 17.5% under severe and extreme stress, while phnW decreased by 13.3% under extreme stress. Correlation analysis showed that in the rhizosphere, soil electrical conductivity (EC) and salinity were positively correlated with several genes, whereas root traits were generally negatively correlated with them. Among root exudates, quinones were positively correlated with phoA, 3-Phytase, phnL, and phnM, whereas terpenoids and stilbenes showed negative correlations. PLS-SEM further indicated that salt stress enhanced soil EC (path coefficient = 0.882, P<0.001), which inhibited root exudation (terpenoids, stilbenes, quinones; path coefficient = -0.79, P<0.001), subsequently influencing the abundances of rhizosphere organic P mineralization genes (path coefficient = -0.49, P<0.05) (R2=0.72). In bulk soil, salt stress primarily affected phoA by altering soil properties and inhibiting exudates (R2=0.82).【Conclusion】??Salt stress differentially impacts the relative abundances of organic P mineralization genes in the rhizosphere and bulk soil of P. distans, with the rhizosphere exhibiting a more pronounced adaptive response. By altering electrical conductivity and simplifying root architecture, salt stress further reshapes root exudation patterns, which in turn regulates the relative abundances of rhizosphere microbial organic P mineralization genes, thereby contributing to plant P acquisition strategy. These findings provide molecular insights into the salt tolerance mechanisms of P. distans and offer a theoretical basis for the sustainable use of saline-alkali soils.

Abstract:Extracellular polymeric substances (EPS), as a key component of soil organic carbon (SOC) sequestration, have long been overlooked. Although the prevalent theories emphasize microbial cell residues as the dominant contributor to SOC formation, emerging evidence indicates that EPS is widely present in soils and is produced at rates comparable to or even higher than cellular biomass, representing a major pathway of microbially derived carbon input into soils. This review systematically synthesizes current knowledge, with a focus on the distinctive role of EPS in soil carbon stabilization. We summarized four key mechanisms through which EPS promote soil organic carbon stability: the formation of mineral-associated organic matter, participation in geopolymerization reactions, driving the formation of soil aggregates, and regulating pore structure. This reveals the pathway for achieving carbon sequestration through both direct and indirect effects. Following our findings, we outline future research priorities, emphasizing the need to develop reliable extraction and quantification methods, incorporate EPS dynamics into SOC models, and elucidate the environmental and microbial factors regulating EPS production and degradation. Addressing these gaps will significantly advance our understanding of microbial roles in the global carbon cycle and inform strategies for enhancing soil carbon sequestration.

Abstract:Shajiang black soil is a major cultivated soil type distributed in the Huang–Huai–Hai region of China. It is characterized by a heavy clay texture, compact structure, low organic matter content, and poor nutrient availability. In recent years, the acidification of Shajiang black soil has become increasingly prominent due to multiple factors, including long-term intensive fertilization, acid deposition, and nutrient removal by crops. This issue has emerged as one of the key constraints on sustainable agricultural development in the region. Soil acidification not only weakens the buffering capacity and nutrient-supplying capacity of Shajiang black soil but also leads to soil structural degradation, microbial community imbalance, and reductions in crop yield. This review synthesizes current research progress on the acidification of Shajiang black soil, with a focus on its status and characteristics, major driving factors, and underlying mechanisms, as well as commonly applied amelioration and management strategies. Furthermore, it analyzes contemporary research hotspots and future development directions, and proposes a classification-based prevention and mitigation framework centered on optimizing tillage systems, improving nutrient resource management, selecting appropriate soil amendments, and enhancing biological synergistic interactions. This framework can provide scientific guidance for the graded amelioration and fertility restoration of acidified Shajiang black soil.

Abstract:【Objective】 This study aimed to investigate the erosion characteristics and sediment carbon loss patterns at different slope positions in the long and gentle slope farmland of the black soil region in Northeast China. The research focused on the full - growth - period coverage of soybean and maize, and at the same time, optimized the cover management factor (C - factor) model to provide a theoretical basis for erosion control and carbon sequestration in this specific geographic area. 【Method】 The research was conducted in the Fuhe small watershed of Bin County, Heilongjiang Province. Runoff plots were established at three distinct slope positions: the upper slope, middle slope, and lower slope. Through in situ artificial simulated rainfall experiments, the study systematically analyzed the impacts of soybean and maize coverage on runoff generation, sediment yield, and sediment carbon loss. The dynamic relationship between water and sediment was explored. Furthermore, by integrating two key vegetation parameters, crop coverage and plant height, a comprehensive and optimized C - factor model was constructed to improve prediction accuracy. 【Result】 The results demonstrated that under the coverage of soybean and maize, the runoff and sediment yield in all plots followed a "V"-shaped trend, initially decreasing and then increasing as the crop growth periods progressed. The optimal stages for reducing runoff and sediment were identified as the beginning of the grain filling stage for soybean (with reduction rates of 33.76%~40.33% and 89.96%~94.54%, respectively) and the tasseling stage for maize (46.32%~54.23% and 92.67%~96.29%, respectively). Comparatively, maize exhibited superior erosion resistance capabilities to soybean. Regarding spatial distribution, the erosion sensitivity across different slope positions followed the hierarchy of lower slope > middle slope > upper slope. Statistical analysis showed that runoff volume, sediment yield, and sediment concentration in runoff were all highly significantly negatively correlated with both crop coverage and plant height. The optimized model integrating these parameters (C = -0.595log(0.01V)×(0.00491H+1.65048)) demonstrated a significant improvement, reducing the root mean square error (RMSE) by 59% compared to traditional models. Additionally, sediment carbon loss was significantly negatively correlated with crop coverage and plant height. Maximum crop coverage was found to reduce total sediment carbon loss by 91.04%~96.12%, with the most effective stages being soybean grain filling and maize tasseling. Notably, 32.65%~69.91% of the total sediment carbon loss was contributed by large sediment particles (> 0.25 mm). 【Conclusion】 This study successfully reveals the specific patterns of soil and sediment carbon loss under the full-growth-period coverage of large-grain crops on long and gentle slopes in the black soil region. The research highlights the critical role of crop phenology and slope position in influencing erosion processes. The findings and the optimized C-factor model provide a robust theoretical foundation for developing effective erosion prevention measures and enhancing carbon sequestration strategies in the long and gentle slope farmland of the Northeast China black soil region.