Abstract:【Objective】This study aimed to investigate the possible contribution of Fe isotopic composition to weathering and pedogenic processes and the formation of Fe-Mn nodules.【Method】Representative soil profiles were established in the warm-temperate, subtropical, and tropical zones in eastern China. The physical and chemical properties, geochemical characteristics, and Fe isotopic compositions of the soils and Fe-Mn nodules were analyzed. 【Result】The results indicated that the degree of pedogenic weathering of the soils from the different climatic zones was mainly controlled by climatic factors, and was also related to the parent materials. The ferromanganese nodules produced in the different climatic zones were all enriched in Fe and Mn, but varied greatly in geochemical characteristics. The ferromanganese nodules developed from tropical basalt have total Fe (Fet) and free Fe (Fed) content of 353.7 mg·g-1 and 293.5 mg·g-1, respectively. These were significantly higher than those of the nodules formed from the Quaternary red clay in the subtropical and the eluviated cinnamon soil in the warm-temperate zone. However, the Fe isotopic composition in the red or cinnamon soils developed from the different climatic zones and different parent materials was similar, and their δ56Fe value varied between 0.018‰ and 0.120‰, all close to the baseline of the continental crust igneous rock. In contrast, the δ56Fe value of the ferromanganese nodules formed in the three climatic zones was all negative, with an average of -0.330‰, which was significantly enriched in light Fe isotopes. 【Conclusion】These results showed that there was a trend of lightening in Fe isotopes of the ferromanganese nodules from the tropical to the subtropical to the warm-temperate zones.

Abstract:【Objective】This study aimed to examine the impacts of microbial diversity loss on paddy soil multifunctionality, and elucidate the regulatory roles of abundant, moderate, and rare microbial taxa. 【Method】Microbial diversity gradients (D0, D1, D3, D6) were established via the dilution-to-extinction approach and functional genes involved in C, N, P, and S cycling in topsoil (0-20 cm) and subsoil (40-60 cm) of a paddy field were quantified using high-throughput quantitative PCR. Soil multifunctionality was assessed using both the averaging and multi-threshold methods. High-throughput sequencing was employed to analyze the diversity, community structure, and co-occurrence network properties of the three microbial taxa and their relationships with soil multifunctionality. 【Result】Results showed that the responses of soil multifunctionality in topsoil and subsoil to microbial diversity loss were different. Compared with the original soil (D0), the averaging method indicated that different dilution levels (D1, D3, D6) significantly reduced topsoil multifunctionality. The reduction rates were 75.8%-85.8%, 74.6%-80.0%, and 59.8%-64.8% under the rice-fallow (RF), rice-wheat (RW), and rice-milk vetch (RM) cropping systems, respectively, with no significant differences among the dilution levels. In contrast, although subsoil multifunctionality showed minor fluctuations (ranging from 0.05 to 0.28), no significant differences were observed between different dilution levels and the original soil except for the D3 treatment under the RM cropping system. This pattern was further verified by the multi-threshold method. Although the diversity of all three taxa significantly decreased with increasing dilution, the community structure of rare taxa remained relatively stable. Co-occurrence network analysis revealed that topological properties (degree, clustering coefficient) of all three taxa decreased significantly in topsoil under dilution. In contrast, rare taxa in subsoil maintained stable network properties despite dilution. Correlation analysis further indicated that topsoil multifunctionality was closely linked to the diversity, composition, and network topology of all three microbial taxa, while subsoil multifunctionality was primarily associated with the degree and clustering coefficient of rare taxa, which underscores the key role of rare taxa in sustaining subsoil multifunctionality in the face of microbial diversity loss. 【Conclusion】Microbial diversity loss induces differential responses of soil multifunctionality in topsoil and subsoil, which is closely related to the diversity, community structure, and co-occurrence networks of microbial subcommunities in different soil layers.

Abstract:【Objective】Greenhouse vegetable systems, characterized by greenhouse covering, intensive fertilization, and frequent irrigation, create a semi-closed, warm, and humid microenvironment that more readily intensifies nitrification-driven nitrogen losses and greenhouse gas emissions compared with open-field vegetable systems. Greenhouse and open-field vegetable systems differ markedly in their environmental conditions, which may lead to variations in the intensity of nitrification and the level of nitrous oxide (N2O) production. However, the seasonal dynamics of nitrification activity and N2O production, as well as the underlying community response mechanisms under different management practices, remain poorly understood. 【Method】Soil samples were collected bimonthly (January to November) from representative greenhouse and open-field vegetable systems in Changshu, Jiangsu Province, China. Meanwhile, in situ N2O was collected from the vegetable field using the static chamber method. A microcosm experiment with combined inhibitors was employed to quantitatively assess the annual dynamics of nitrification activity and N2O production driven by complete ammonia-oxidizing bacteria (Comammox) and conventional ammonia-oxidizing microorganisms (Ammonia-oxidizing bacteria, AOB and Ammonia-oxidizing archaea, AOA). The absolute abundances of these microbial groups were determined using quantitative real-time PCR (qPCR) targeting the amoA gene. Additionally, high-throughput sequencing of the amoA gene was conducted to characterize the seasonal shifts in community structure and their responses to different management regimes. 【Result】Results showed that in situ N2O flux in greenhouse vegetable soils was significantly higher than that in open-field vegetable soils, with a pronounced “hot-moment effect” in March and May, contributing 71.23%±25.50% of the annual total flux. Soil nitrification activity exhibited a pronounced “hot-moment” effect in July and September, accounting for 52.41%±1.59% of the annual total, which coincided with the highest N2O production potential (61.35%±9.24% of the annual release). Functionally, the nitrification process and N2O production were predominantly mediated by AOB in greenhouse vegetable soils, whereas AOA dominated in open-field vegetable soils. The greenhouse vegetable system promoted the accumulation of Comammox abundance but suppressed its nitrification function, whereas both the abundance and activity of AOB were significantly enhanced. Correlation analysis revealed that soil temperature, dissolved organic carbon (DOC) and soil pH were the primary drivers of nitrification, while nitrate and DOC were the main factors shaping microbial community composition. 【Conclusion】This study elucidates the influence of differentiated management practices on the nitrification processes of soil nitrifying microorganisms, and demonstrates that the shift from open-field to greenhouse vegetable systems may increase AOB-driven N2O production. These findings provide a scientific foundation for optimizing nitrogen management and developing N2O mitigation strategies in vegetable cultivation systems.

Abstract:【Objective】Determining the patterns of regulatory factors of soil extracellular enzyme activity along elevational gradients is critical for understanding microbial nutrient limitation and metabolic processes. This contributes to predicting the responses of soil biogeochemical cycles to global change. However, knowledge of the elevational patterns in soil extracellular enzyme activity and their stoichiometry, as well as their drivers, remains limited. 【Method】Soil samples (0-10 cm) were collected from different elevation gradients on Jinzhongshan Mountain in Guangxi, China. These samples were used to investigate the elevational patterns of soil physical and chemical properties, extracellular enzyme activities, and microbial nutrient limitations. Also, the major factors influencing microbial extracellular enzyme activities and their stoichiometry were evaluated. 【Result】 The results indicate that (1) soil water content (SWC), soil nutrient content, stoichiometric ratios, and microbial biomass content increased with increasing elevation. However, soil bulk density (BD), pH, and available phosphorus (AP) content decreased with increasing elevation. (2) The activities of carbon and nitrogen degradation-related enzymes, including β-glucosidase (BG), N-acetylamino glucosidase (NAG), and leucine aminopeptidase (LAP), exhibited no clear pattern with increasing elevational gradient. In contrast, acid phosphatase (ACP) activity initially increased, then decreased along with elevation, presenting a unimodal pattern. Vector analysis of ecoenzyme activities revealed that vector lengths were larger at middle and high elevations (1 429-1 691 m), suggesting an enhanced carbon limitation for soil microorganisms. Additionally, all vector angles were greater than 45°, indicating a widespread phosphorus limitation for soil microbes in the study region. (3) Compared with soil enzyme activity data at the global scale and in Chinese regions, soil enzyme activities related to carbon, nitrogen, and phosphorus cycling in Jinzhongshan, which is located in the transition zone from the eastern humid region to the western semi-humid and semi-arid region, were generally low. This suggested that soil microorganisms in this area were subject to relatively greater N and P limitations. Furthermore, compared to soils in humid regions, the activities of C-, N-, and P-cycling enzymes were lower, whereas the activities of enzymes associated with C and P cycling were relatively higher when compared with arid regions. (4) Mantel test results indicated that soil extracellular enzyme activity and their stoichiometry were significantly correlated with SWC, NO3--N, and microbial biomass nitrogen (MBN). Redundancy analysis (RDA) revealed that NO3--N and microbial biomass phosphorus (MBP) were the key factors driving variations in soil extracellular enzyme activities, whereas soil enzyme stoichiometry was primarily regulated by NO3--N, total phosphorus (TP), C:N, and MBP. (5) Partial least squares path modeling (PLS-PM) demonstrated that soil physical properties and microbial biomass directly influenced soil extracellular enzyme activities, whereas soil physicochemical properties together with microbial biomass exerted direct effects on enzyme stoichiometry.【Conclusion】Elevation affected extracellular enzyme activities mainly through regulating soil physical properties and microbial biomass, but indirectly modulated enzyme stoichiometry via altering soil physicochemical properties and microbial biomass. These findings contribute to enhancing the mechanistic understanding of how soil extracellular enzyme activities and their stoichiometric patterns respond to elevation gradients in mountain forest ecosystems under global climate change.

Abstract:【Objective】This study aimed to explore the effects of the coupling of different biochar application depths and cropping patterns on the soil carbon pool and crop yield. 【Method】A long-term stationary experiment established in 2019 was adopted, with cropping pattern as the main plot and biochar application method as the subplot. Three cropping patterns were designed: soybean-maize rotation (SM), continuous soybean cropping (S), and continuous maize cropping (M). Three treatments were set up: biochar mixed application at 0-20 cm (B1), biochar mixed application at 0-40 cm (B2), and no biochar application (CK). Soil samples were collected from the 0-20 cm and 20-40 cm soil layers at the crop maturity stage in 2023, and the soil carbon fractions, humus components, and crop yield were determined. 【Result】The results showed that: the contents of soil carbon fractions (e.g., soil organic matter (SOM) and microbial biomass carbon (MBC)) in the rotation system were significantly higher than those in continuous cropping systems, and the SOM content under continuous soybean cropping was significantly higher than that under continuous maize cropping. The application of biochar at 4 500 kg?hm-2 had no significant effect on SOM content in the 0-20 cm soil layer, but it increased the activity of MBC in the 0-20 cm soil layer (by 11.3%-33.7%), optimized humus properties (humic acid (HA) content increased by 6.7%-25.7% while fulvic acid (FA) content decreased by 0.4%-22.5%). This treatment also improved crop yield (soybean yield increased by 24.2%-32.4% and maize yield increased by 13.0%-24.3%). Under the synergistic effect of rotation and biochar application, MBC content increased by 22.8%-33.7%, dissolved organic carbon (DOC) content increased by 17.6%-31.1%, readily oxidizable organic carbon (ROC) content increased by 14.9%-26.6%, HA content increased by 14.5%, FA content increased by 11.8%-15.5%, and the humus quality index (PQ) increased by 11.7%-17.4%.【Conclusion】The coupling of biochar application and crop rotation is beneficial for improving the soil carbon pool, enhancing carbon activity, optimizing humus properties, and increasing crop yield. This practice is expected to play an important role in future agricultural production and soil environment improvement.

Abstract:【Objective】This study aimed to elucidate the mechanism by which sorbitol-chelated potassium (SK) promoted nutrient uptake and utilization in wheat leaves.【Method】In this study, sorbitol-chelated potassium was used as the test foliar fertilizer and wheat cultivar Tainong 108 as the experimental material to elucidate the effects of foliar application of different potassium forms on leaf physiological and biochemical traits as well as phyllosphere microbial community structure. Structural equation modeling (SEM) was further employed to quantify the contribution of each factor to wheat yield, thereby providing a theoretical basis for the yield-enhancing mechanisms of chelated potassium fertilizers.【Result】Results from two consecutive field seasons showed that, compared with potassium chloride (K) and a mixture of sorbitol and potassium chloride (S+K), the SK treatment significantly affected wheat leaf physiological and biochemical characteristics and bacterial richness. (1) Mean yield increases were 24.74% and 18.76%, respectively. (2) Grain Mn concentration increased by 16.14% and 12.12%, grain K by 45.68% and 21.96%, late grain-filling stage leaf K by 81.01% and 24.44%, and maturity satge leaf C by 2.52% and 1.95%. (3) Activities of catalase, peroxidase and superoxide dismutase were better maintained, while malondialdehyde content decreased by 25.65% and 7.51%; the activities of protein synthesis enzymes (nitrate reductase, glutamine synthetase and glutamate-pyruvate transaminase) were sustained during mid-to-late grain filling satge. (4) Relative abundance of Firmicutes rose by 57.36% and 50.00%, whereas Actinobacteria declined by 21.63% and 4.26% and Cyanobacteria by 36.05% and 62.03%.【Conclusion】SK treatment enhanced yield and grain quality through the synergistic regulation of wheat leaf element content, antioxidant capacity and protein synthesis enzyme activities. SEM further demonstrated that all measured indicators were directly or indirectly linked to final grain yield.

Abstract:【Objective】This study aimed to explore the response of functional traits of leaves and the antioxidant enzymes of Fraxinus malacophylla seedlings to rainfall characteristics in different rocky desertification habitats.【Method】This study focused on 2-year-old F. malacophylla seedlings and adopted a two-factor randomized block design. Different karst habitats were set up, including no stone whole soil S0 (all soil layers), half stone half soil S1/2 (upper 1/2 was soil layer, lower 1/2 was Karst layer), and more stone less soil S3/4 (upper 1/4 was soil layer, lower 3/4 was Karst layer), as well as different rainfall time intervals of 3 days (I3d), 6 days (I6d), and 9 days (I9d). During the experiment, the growth and physiological changes characteristics of F. malacophylla seedlings in different Karst habitats were analyzed.【Result】The results showed that under the same rainfall time interval, the root biomass of F. malacophylla seedlings increased with the increase of rock coverage (P<0.05), while the stem and leaf biomass showed a trend of first increasing and then decreasing. As the thickness of Karst increases, the biomass accumulation of various organs from high to low was in the order of roots, stems, and leaves. Under a 3-day rainfall treatment, the leaf area, leaf circumference, leaf length, leaf width, and potassium (K+), calcium (Ca2+), sodium (Na+), and magnesium (Mg2+) contents in various organs of F. malacophylla seedlings increased with the increase of rock coverage (P<0.05). Also, the S3/4 Karst habitat with 6-day and 9-day interval rainfall significantly inhibited the leaf traits and accumulation of K+, Ca2+, Na+, and Mg2+contents in F. malacophylla seedlings. F. malacophylla seedlings adapt to different Karst habitats through various physiological and biochemical regulation strategies, including biomass allocation optimization, interorgan nutrient transport strategies such as Na? transfer to stems, Ca2?/Mg2? enrichment in leaves, reduction of leaf number (LN), activation of superoxide dismutase (SOD), and peroxidase (POD) enzyme activities, and increase soluble protein (SP) content.【Conclusion】In summary, a 6-day rainfall interval and a half stone and half soil habitat (I6dS1/2) are the optimal combination for seedling growth. This study provides a theoretical basis for the cultivation and promotion of F. malacophylla seedlings under different levels of rocky desertification in the southwestern Karst region. It is recommended to adopt a water replenishment interval of about 6 days for afforestation and nurturing in areas with moderate rocky desertification.

Abstract:【Objective】Thermal desorption technology is widely applied in the remediation of petroleum-contaminated soil. However, the significant differences in the thermal desorption characteristics due to different types of clay mineral, significantly impact the setting of process parameters and the efficiency of thermal desorption. Thus, this study aims to clarify the differences in thermal desorption mechanisms among various petroleum-contaminated clay minerals and to guide the determination of application parameters for thermal desorption engineering.【Method】In this study, contaminated soil with typical clay minerals including montmorillonite, chlorite and kaolinite were prepared to investigate the thermal desorption kinetic properties, and characterize their microstructures to explore the differences in thermal desorption and the influencing factors. 【Result】The results showed that the thermal desorption of three contaminated soil could be divided into three stages. Phase I (30 ℃-110 ℃), in this phase, montmorillonite and chlorite exhibited a three-dimensional diffusion desorption mechanism, while kaolinite followed a first-order kinetic desorption mechanism. The activation energies (Ea) were 58.64, 124.96 , and 75.22 kJ mol-1, respectively. Phases II (110 ℃-370 ℃) and III (370 ℃-520 ℃) followed a first-order kinetic mechanism. 【Conclusion】The physicochemical properties and microstructure of clay minerals are the main parameters accounting for the differences in their thermal desorption characteristics. Montmorillonite mainly relied on azeotropic stripping, diversion diffusion, catalytic cracking, and interlayer structure adsorption, which promoted the thermal desorption of petroleum hydrocarbons. The influencing mechanism of chlorite involved physical barrier and catalytic cracking, showing an inhibitory effect at temperatures <200 ℃. However, thermal desorption of petroleum hydrocarbons was promoted when the temperature was >200 ℃. The influencing mechanism of kaolinite was mainly chemical adsorption, which generally inhibited the thermal desorption of petroleum hydrocarbons. This study provides theoretical guidance for determining the thermal desorption process parameters of petroleum-contaminated soils containing different types of clay minerals.

Abstract:【Objective】The interactions between heavy metals and mineral particles play a key role in the passivation/activation of heavy metals, significantly impacting on soil health, food safety and ecological stability. However, quantitative characterization of the type and intensity of these interactions remains challenging. 【Method】Based on orbital hybridization theory, this study quantitatively evaluated the polarization, polarization-induced covalent interactions and Coulomb interactions of the heavy metal Pb2+ on mineral surfaces.【Result】The results show that: (1) The surface charge number follows the order: montmorillonite > silica > kaolinite > hematite. However, the order of surface negative charge density and electric field strength is kaolinite > silica > montmorillonite > hematite, due to differences in specific surface area. (2) The adsorption capacity of Pb2+ depends on the surface charge number, consistent with its trend, while the adsorption strength is governed by the surface electric field. (3) Effective charge coefficients of Pb2+ on soil mineral surfaces, quantified using orbital hybridization theory, averaged as follows: kaolinite (1.848 ± 0.038) > montmorillonite (1.782 ± 0.062) > silica (1.615 ± 0.029) > hematite (1.516 ± 0.036). Based on the effective charge coefficient, the type and intensity of the adsorption force of Pb2+ on mineral surfaces could be assessed. (4) The adsorption of Pb2+ on the surfaces of montmorillonite, kaolinite, and silica is primarily driven by Coulombic forces, which account for more than half of the total adsorption energy. In contrast, adsorption on the surface of hematite is mainly governed by covalent interactions, contributing approximately 65%. Additionally, polarization effects depended on the surface electric field and polarization-induced covalent interactions play a crucial regulatory role in the adsorption of Pb2+. (5) Infrared spectroscopy analysis revealed that the absorption peak of the Si-O bond on the surface of silicon-containing minerals shifted to higher frequencies (blue shifts) as the surface electric field increased. This shift indicates an enhanced polarization-induced covalent interaction between O atoms and Pb2+ on the mineral surfaces. Also, the strong electric field on the surface of hematite enhances the polarization of the -OH group and H2O molecules, leading to the formation of covalent interactions between Pb2+ and -OH groups. Consequently, the Fe-O-Fe bonds are strengthened as the pH increases. 【Conclusion】This study demonstrates that the adsorption of Pb2+ on the surface of soil minerals has polarization and polarization-induced covalent effects, and quantitatively evaluates its contribution. The effective charge coefficient of Pb2+ increases with the increase of surface electric field strength, and the polarization and polarization-induced covalent interaction between mineral surface and Pb2+ increase with the increase of pH. This indicates that polarization and polarization-induced covalent interaction have an important influence on the interaction between Pb2+ and the mineral surface. Additionally, this research establishes a theoretical foundation for the directional regulation of heavy metal passivation/activation in soils through modulation of interfacial forces.

Abstract:The growth and evolution of biofilms in porous media involve complex coupled physicochemical and biological processes. Their pronounced multi-scale characteristics, heterogeneity of the media, and uncertainties in model parameterization have led to fundamental divergences in the theoretical frameworks of numerical models across different scales. This poses significant challenges for the accurate characterization and prediction of biofilm dynamics. In recent years, advances in computational techniques have driven substantial progress in pore-scale, continuum-scale, and cross-scale coupled numerical modeling and simulation of biofilm growth. However, considerable bottlenecks remain in model development, validation, and utilization. These include difficulties in characterizing three-dimensional microscopic pore structures, the complexity of constructing biofilm growth dynamics models, the lack of quantitative standards for cross-scale multiprocess coupling strategies, and the scarcity of experimental data required for model parameterization. Based on the mechanisms of biofilm growth dynamics in porous media, this paper reviews the research progress of pore-scale, continuum-scale, and multi-scale coupling numerical models, analyzes the theoretical foundations, numerical algorithms, application cases, applicability, and limitations of biofilm growth models at different scales. It also summarizes the application potential of three-dimensional imaging technologies, outlines the emerging trends in mechanistic representation of the complete biofilm growth processes, and explores the optimization pathways for cross-scale coupling modeling strategies. This review provides a theoretical basis for the selection and improvement of biofilm growth models, and offers technical support for the engineering application of soil microbial technologies in environmental pollution control and ecological restoration.