Compost-derived humic acids (HAs) and fulvic acids (FAs) play an essential role in enhancing soil microbial diversity and activity by facilitating metabolic processes through electron transfer. Herein, the effect of bioleaching dewatered sludge (BDS) in comparison with filter press dewatered sludge (FDS) on the electron transfer capacity (ETC) of humic substances during composting was investigated as a novel attempt. A variety of characterization methods including UV-Vis, FTIR, 3D-EEM, and electrochemical measurements, were used to explore the change in humic substances during composting. The results indicated that bioleaching treatment significantly influenced the organic matter composition and hindered the accumulation of redox-active functional groups during composting. Notably, the ETC of HA increased by 24.07% in the FDS group but declined by 40.62% in the BDS group. This divergence stemmed from the organic matter loss during bioleaching, leading to reduced quinone-like and tryptophan-like substances associated with electron transfer in HA during composting. Furthermore, BDS showed lower pH, water content, and organic matter, but higher concentrations of ammonium nitrogen (NH4+-N) and ammonia nitrogen NH3--N, all of which potentially influenced humification efficiency. These findings not only clarify the electron-transfer dynamics of humic fractions but also highlight the importance of optimizing sludge pretreatment for improved composting performance and resource recovery.

Sloping cropland faces accelerated soil erosion and rocky desertification due to long-term cultivation and rainfall, becoming a major ecological issue in Southwest China's karst region. This study focuses on soil from karst sloping croplands (Calcaric Cambisol) under continuous cultivation for 2, 8, 13, 18, 25, and 30 years. We used wet sieving, the Le Bissonnais (LB) methods, and concentrated flow scouring experiments, to evaluated the distribution, stability, and erosion resistance of soil aggregates, and assess the impacts of cultivation duration on soil physicochemical properties, aggregate breakdown, and detachment-transport mechanisms. Results demonstrated that continuous cultivation reduced soil organic carbon (SOC) from 37.33 to 17.02 g kg−1, cation exchange capacity (CEC) decreased by 39.04 %, clay content dropped from 44.89 % to 35.53 %, while sand content increased from 19.37 % to 28.90%, leading to marked deterioration of soil structure and erosion resistance. Both wet sieving and LB analyses revealed a decrease in > 2 mm aggregates (down by 41.10 %), while the 0.25–0.1 mm and < 0.1 mm fractions increased and mean weight diameter (MWD) decreased by 50.70 %. The soil erodibility (K-Factor) increased by 5.20 %, and the relative sensitivity index (RSI) increased by 22.04. Under concentrated flow, the content of > 5 mm aggregates declined by up to 58.38 %, while MWD decreased by up to 2.04 mm. Correlation and machine learning analyses revealed that aggregate stability was most influenced by SOC, pH, CEC, and clay content. This study provides new insights into soil detachment mechanisms in karst sloping croplands and offers scientific support for sustainable management.

Living cover crops are increasingly used in orchards, but evidence linking cover-crop identity to earthworm indicators under subtropical conditions remains limited. This cross-sectional field comparison was based on one sampling event in November 2025. We compared perennial peanut (Arachis pintoi) and Indigofera hendecaphylla Jacq. ex Poir. with a weedy control and measured community-level earthworm abundance and fresh biomass, plant-derived inputs, and selected soil properties at 0–10 and 10–20 cm. Mixed-effects models accounting for the randomized block design detected treatment- and depth-associated differences in earthworm abundance and biomass. At 0–10 cm, I. hendecaphylla had the highest earthworm abundance (156.00 ± 40.92 ind. m⁻²) and fresh biomass (2.408 ± 0.365 g m⁻²). Across 0–20 cm, total abundance and fresh biomass were 78.1% and 93.3% higher, respectively, under A. pintoi than under the weedy control, and 208.2% and 218.3% higher under I. hendecaphylla. I. hendecaphylla also had the highest litter standing crop (625.89 ± 32.45 g fresh mass m⁻²) and the highest topsoil organic matter, total nitrogen, and alkali-hydrolyzable nitrogen. Correlation and ordination analyses summarized associations with surface litter and nutrient-related variables but did not establish independent drivers or causality. At this single November sampling event, both living covers were associated with higher earthworm abundance and fresh biomass, with the strongest association under I. hendecaphylla. Temporal persistence requires multi-season sampling, dry-mass measurements, and species or ecological-group identification.

The cocontamination of arsenic (As) and cadmium (Cd) in agricultural soils poses severe risks to ecosystem stability and food safety because of their high toxicity, mobility, and bioaccumulation potential. However, single amendments often exhibit selective immobilization, which limits their effectiveness for As-Cd-cocontaminated soils. In this study, a sepiolite-supported nanoscale zero-valent iron composite (S-nZVI) was synthesized via liquid-phase reduction, and its remediation performance and mechanisms under different moisture conditions were evaluated. The characterization results confirmed that the nZVI nanoparticles were uniformly dispersed and anchored onto the sepiolite matrix, thus mitigating aggregation and oxidative passivation while increasing surface reactivity. Soil incubation experiments demonstrated that S-nZVI reduced the bioavailability of As and Cd and promoted their transformation from labile to stable fractions under both 50% and 120% water holding capacity (WHC). Under flooded conditions (120% WHC), 0.5% S-nZVI reduced the bioavailable Cd and As concentrations by 52.3-58.7% and 67.4%, respectively, after 120 days. Mechanistically, immobilization was governed by a synergistic "adsorption-reduction-coprecipitation" pathway coupled with pH-Eh regulation. Rice pot experiments further validated the effectiveness of S-nZVI, with the grain As and Cd concentrations reduced by 73.3% and 52.3%, respectively, without impairing plant growth. Overall, S-nZVI provides an efficient strategy for simultaneous immobilization of As and Cd in As-Cd-cocontaminated soils and supports the safe use of polluted agricultural lands.

In karst agroecosystems, the stability of soil organic carbon (SOC), which is essential for sustainable land management, is strongly influenced by the carbonate parent material. However, how land use and lithology interactively affect the vertical distribution and stabilization of SOC fractions remains unknown. This study investigated the vertical distribution (0–70 cm) of SOC fractions (particulate, POC; mineral–associated, MOC; recalcitrant, ROC; microbial biomass, MBC; dissolved, DOC; permanganate–oxidizable, LOC) in paddy and upland systems overlying limestone and dolomite. Results showed that land use and lithology jointly determined depth–dependent patterns of SOC fractions. The key finding was a depth–dependent reversal of land use effects: paddy soils had higher concentrations of SOC fractions (especially MBC and LOC) in the top 0–20 cm, whereas upland soils had higher concentrations of DOC, ROC, and POC below 50 cm. This pattern underscores an overlooked deep carbon sequestration potential in aerated uplands. Furthermore, lithology exerted fundamental control on SOC stability, with limestone soils exhibiting higher MOC/SOC and MOC/POC ratios than dolomite soils, indicating stronger organo–mineral association. Random Forest and Structural Equation Modeling revealed that soil aggregate stability is a key factor influencing the stability of SOC. These findings demonstrate that effective SOC management in karst agroecosystems must consider both surface land use decisions and deep lithological constraints. Specifically, promoting aggregate stability offers a more targeted pathway for long–term carbon stabilization in these ecologically fragile agricultural systems.

Climate-exacerbated urban waterlogging imposes severe hypoxic stress on mesophytes. However, whether mesophytes possess dissolved oxygen (DO)-driven mechanisms for adaptive structural and physiological remodeling remains poorly understood. We conducted a hydroponic experiment with four representative mesophyte species (Gardenia jasminoides, Murraya paniculata, Ixora chinensis, and Heptapleurum actinophyllum 'Variegata') across four DO gradients (0-2, 2-4, 4-6, and 6-8 mg/L). Plant growth, physiology, and root anatomy were measured, and structural equation modeling (SEM) was applied to disentangle the synergistic pathways underlying waterlogging tolerance. We identified a critical DO threshold: concentrations below 2 mg/L triggered irreversible root degeneration and substantial mortality (50% in I. chinensis), whereas 4-8 mg/L represented the optimal range for maintaining normal growth and 100% survival. Mechanistically, moderate-to-high DO (4-8 mg/L) induced a coordinated shift in functional traits. SEM revealed that DO directly promoted aerenchyma formation (β = 0.77), enhanced internal oxygen transport to mitigate ROS accumulation and significantly reduced membrane lipid peroxidation (MDA, β = -0.39). Concurrently, DO activated the antioxidant enzyme system (β = 0.73) and proline osmoregulation (β = 0.40) to scavenge residual ROS, while increased chlorophyll a content drove plant height (β = 0.90) and biomass accumulation. The four species exhibited distinct adaptive strategies: I. chinensis (structural adaptation), G. jasminoides (physiological compensation), M. paniculata (root reinforcement and osmoregulation), and H. actinophyllum 'Variegata' (synergistic aboveground-belowground growth). This study advances mechanistic understanding of mesophytic stress tolerance under oxygen fluctuations and identifies DO-driven structural-physiological pathways as a reference for plant waterlogging adaptation research.

Using a high-boiling alcohol system to dismantle main components of biomass is a feasible technology. Reducing dismantle operating costs and improving dismantle efficiency are essential for promoting the green, economical, and sustainable development of biomass refining. Therefore, based on the low cost and chemical properties of H2O at high temperature, the effects of different H2O dosages in NaOH-catalyzed ethylene glycol (HBAA) system on the dismantling efficiency of bagasse, surface lignin coverage, recovered-lignin activity and enzymatic hydrolysis efficiency were investigated. Compared with the HBAA dismantling system without H2O, the HBAA system with 60% w/v H2O can obviously increase the removal rates of lignin and hemicellulose, while recovering up to 99% of cellulose and significantly declining surface lignin coverage, thus enhancing the enzymatic hydrolysis efficiency. Additionally, the results of density functional theory calculations and 2D HSQC NMR analysis prove that the synergy between H2O and ethylene glycol can promote the esterification reaction occurrence at the alpha-C carbon cation in beta-O-4 structure of lignin, thereby protecting the beta-O-4 aromatic ether bond. Simultaneously, when the H2O dosage increase from 0% to 60%, the enzymatic yield increases from 84.51% to 93.74% with an enzyme load of 10 FPU/g. Based on experimental results, this study conducted a techno-economic analysis of bagasse dismantling for ethanol and co-production of lignin, achieving a minimum ethanol selling price of $1.07 per kg. In this study, a green and economical solution for dismantling the main components of bagasse is developed, which is important for the high-value conversion of bagasse.

Green manure-tobacco rotation represents a promising strategy for modulating root-associated microbiome, offering significant potential to enhance crop productivity and support sustainable tobacco cultivation in Southwest China. Here, pot experiments including treatments of smooth vetch (SV), ryegrass (R), and radish (RD) as green manures rotated with tobacco were established. The spatiotemporal dynamics of soil microbial species pool and root-associated microbiomes as well as their functional profiles and contributions to tobacco growth were investigated. Results showed that green manures effectively captured soil available nutrients at their growth stage, then SV significantly increased soil inorganic nitrogen, R and RD subsequently increased dissolved organic nitrogen across later tobacco growth. Furthermore, SV significantly increased tobacco shoot and root biomass respectively by 4.4% and 36.1%, and increased tobacco shoot nitrogen content by 0.25%, compared to fallow. Host selection index (HSI) for bacteria and fungi is 2.23 and 3.84 in fallow, while 1.99–2.32 and 1.8–2.79 in green manuring treatments, indicating green manure can mitigate host selection intensity and facilitate the colonization of soil microbiota to root (with the exception of SV bacteria, HSI=2.32). The gradually enriched microbes across soil- root continuum of green manuring treatments dominated by Rhizobiaceae, Sphingomonadaceae and Sordariomycetes, Dothideomycetes, respectively, suggesting that green manuring increased colonization of growth promoting taxa (e.g., diazotrophs and saprotrophs) in. Functional predictions highlighted that the enriched taxa of SV favored nitrogen cycling, R and RD enhanced saprotrophs, showing that green manure differentially facilitated various functional enriched taxa. These findings collectively demonstrate that the SV could be the suitable rotation practice which simultaneously enhance nutrient availability and microbiome-mediated benefits across different green manure treatments, providing insights for targeted soil microbiome management in sustainable agriculture.

Organic fertilizer substitution is increasingly used to reduce chemical nitrogen input in rice production, but the agronomic effects may vary with fertilizer source. This study compared chemical fertilizer alone with seven organic substitution treatments based on rapeseed cake, peanut bran, mushroom residue fertilizer, cattle manure, chicken manure, goat manure, and pig manure under the same nitrogen substitution ratio. Rice yield, grain quality, post-harvest soil physicochemical properties, and integrated performance were evaluated in the 2025 final-year dataset after two consecutive years of continuous fertilization. Responses differed clearly among fertilizer sources. Chicken manure and cattle manure produced the highest grain yields, mainly through stronger effects on grains per panicle, seed-setting rate, and grain filling. Grain quality showed more selective responses: mushroom residue fertilizer resulted in the highest head rice rate, peanut bran increased chalkiness-related traits, and mushroom residue fertilizer and goat manure were associated with higher grain protein content. In contrast to the yield pattern, plant-derived fertilizers, especially rapeseed cake and mushroom residue fertilizer, showed stronger advantages in post-harvest soil improvement. Rapeseed cake produced the highest soil quality index, whereas mushroom residue fertilizer showed the most balanced overall performance across yield, grain quality, and soil variables. These results indicate that the effects of organic fertilizer substitution in rice are strongly source-dependent. Animal-derived fertilizers were more favorable for short-term yield improvement, rapeseed cake was more effective for soil fertility enhancement, and mushroom residue fertilizer provided the best overall balance among productivity, grain quality, and soil improvement.

Soil acidification threatens terrestrial ecosystem functioning. This study aimed to identify pH thresholds for bacterial community structure and diversity using an artificially manipulated pH gradient, and to determine disentangle whether compositional turnover and diversity loss occur synchronously. A pot experiment was conducted with soil pH artificially adjusted to a gradient of 3.8–7.2. Bacterial communities were analyzed by 16S rRNA gene sequencing. TITAN, change-point analysis, segmented regression, co-occurrence network analysis, and structural equation modeling were applied to detect community thresholds, assess network complexity, and evaluate driving mechanisms. Two key pH thresholds were identified. The first threshold emerged at pH 4.3–4.5, below which Shannon diversity remained severely suppressed. The second threshold occurred at pH 5.9–6.0, marking a pronounced reorganization of bacterial community composition. All 2,518 high-confidence indicator OTUs were positive responders (z+), revealing directional asymmetry driven by the proliferation of taxa that had been suppressed under extreme acidity (e.g., Chloroflexota, Pseudomonadota, Actinomycetota). Above pH 5.88, the co‑occurrence network became substantially more complex, with increased edges and nodes, re‑emergence of module hubs, and more connectors, indicating network recovery following pH amelioration. SEM demonstrated a mechanistic shift at pH 5.88: when pH ≤ 5.88, pH, exchangeable aluminum, and available phosphorus jointly explained 70.8

In recent years, the high-value utilization of lignin and its derivatives have received widespread attention. Sulfonated lignin (SL) is an important functional lignin derivative derived from the sulfonation modification of natural or industrial lignin, which has a wide range of applications in several fields. The structural differences of SL directly determine its characteristics, thereby affecting its performance. Based on analyzing the main structure and physicochemical properties of SL, this article summarizes its main application areas, and focuses on different modification strategies in functional application fields such as adsorbents, dispersants, flocculants, and water-reducing agents. Meanwhile, it reviews the role of Density Functional Theory calculations in investigating the mechanisms of structural modification and performance enhancement of SL. Finally, in view of the current limitations in structural regulation of SL, some new strategies are proposed to achieve precise optimization of its performance.

Two constructed wetlands (CWs) included horizontal subsurface flow (HSFCW) and surface flow constructed wetland (SFCW), were established to evaluate performance and underlying mechanisms in removing atrazine and conventional pollutants from non-point source pollution. The introduction of atrazine resulted in a notable decrease in the removal efficiencies for COD, TP and NH4+-N across CWs. Notably, when hydraulic loading rate (HLR) was reduced, a significant recovery was observed in HSFCW, with the removal rates of COD (76.85 ± 12.82%), TP (81.97 ± 2.87%), and NH4+-N (54.14 ± 4.11%) reaching or surpassing the baseline levels of the atrazine-free. In contrast, the removal efficiencies only partially recovered, remaining below their pre-atrazine levels in SFCW. Although the atrazine removal efficiencies reached 50.83 ± 4.86% in SFCW and 59.33 ± 7.50% in HSFCW, removal mechanisms differed. In SFCW, photosynthetic oxygen production and microbial degradation of atrazine were critical steps. Photosynthetic bacteria like Rhodoplanes etc. improved the elimination of organic compound under oligotrophic conditions, and NH4+-N oxidation by creating aerobic condition. Due to the simplicity of their metabolic network, SFCW exhibited compromised resilience when exposed to shock loads or contaminants. In HSFCW, plant uptake, substrate adsorption and microbial decomposition of atrazine, and stress resistance of system played an important role. The anti-adaptive bacterium (Luteimonas, Crenothrix, Sediminibacterium) enabled the HSFCW to maintain robust removal efficiencies for both atrazine and conventional pollutants even under pollutants stress. Four atrazine degradation intermediates were identified and possible metabolic routes were postulated. These findings offer critical insights for optimizing CW designs to mitigate non-point source agricultural pollution.

Jasmine (Jasminum sambac) is a highly valued aromatic plant, widely used for scenting tea and extracting essential oils. Flower quality directly influences the market value of these products. However, the classification of jasmine flowers currently relies on empirical visual inspection and mechanical sieving, lacking objective chemical markers. In this study, freshly picked commercial jasmine buds (grade A and grade B) and fully bloomed flowers (grade I and grade II) were analyzed to examine differences in their volatile compound profiles using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). According to the general commercial grading standards used by growers and tea companies, 25 compounds differed significantly between grade A and grade B buds, while 134 compounds differed significantly between grade I and grade II opened flowers (P < 0.05). Intersection analysis identified six compounds common across grade comparisons. By comprehensively evaluating their fold changes and relative abundances, three compounds—(E)-3-Hexen-1-ol, Caryophyllene, and (E,E)-3,5-Octadien-2-one—were selected as potential markers. Based on the current dataset, the S-score provides an objective, data-driven approach to distinguish jasmine flower grades. However, as a preliminary model, its proposed threshold (S > 9.5) requires independent validation using samples from different seasons, regions, or production batches before any practical application.

Non-point source pollution poses a severe threat to the water quality of the Li River. This study conducted field monitoring of pollution loads from different land-use types on Maozhou Island in the Li River during the 2023 rainy season. Runoff water quality from vegetable plots, orchards, and bamboo forests consistently exceeded standards, with vegetable plots being the primary source of pollution. Their total phosphorus (TP) concentration exceeded standards by nearly 25 times, contributing the highest annual load. The transport of pollutants (TP, total nitrogen(TN), chemical oxygen demand(CODCr)) was closely correlated with suspended solids (SS), with the finest particles (<5 μm) identified as the primary carrier exhibiting the strongest pollutant enrichment capacity (e.g., in vegetable fields, the correlation coefficient r between < 5 μm particles and TP was >0.85, p < 0.01). Rainfall patterns significantly influenced pollutant concentrations; TN and TP levels increased with preceding dry days, while phosphorus output from vegetable plots decreased with rising average rainfall temperature. Compared to bamboo forests, vegetable plots and orchards exhibited lower soil adsorption capacity. This study recommends a connectivity-based strategy prioritizing the interception of heavily enriched fine particulate matter (<5 μm) through runoff control and enhanced wetland retention functions. These findings underscore the importance of controlling fine particulate matter for reducing non-point source pollution and maintaining ecological health in the Lijiang River basin.

Sugarcane is an important perennial economic crop and its long-term continuous ratoon cropping system may induce temporal changes in soil erodibility, yet the underlying mechanisms remain unclear. In this study, a chronosequence design was used to select independent sloping sugarcane fields with continuous cropping durations of 2, 7, 12, and 24 years from a typical subtropical sugarcane-growing region in southern China. Soil physical, mechanical, and chemical properties were measured, and the soil erodibility K factor and comprehensive soil erodibility index (CSEI) were calculated to characterize temporal patterns of soil erodibility under long-term continuous cropping. Results indicated that soil erodibility was relatively high in the early stage (2 years), significantly decreased in the middle stage (7 and 12 years), and increased again in the late stage, with the highest erodibility observed at 24 years. Soil structure was the primary factor driving soil erodibility change. The decrease in erodibility during the middle stage was likely associated with improved aggregate stability supported by organic matter inputs and root activity under reduced tillage. The renewed increase in erodibility during the late stage was closely associated with clay loss, soil coarsening, and topsoil structural degradation. The soil erodibility K factor and CSEI showed similar change trends, and both can be flexibly applied depending on research objectives and data availability. These findings provide a scientific basis for soil erosion risk assessment and sustainable management of subtropical sloping sugarcane farmlands.

The complex lignocellulosic structure of sugarcane leaves poses a major challenge for direct composting, leading to slow degradation and long processing cycles. To address this, efficient pretreatment is crucial for enhancing resource recovery. In this study, a combined potassium hydroxide (KOH) and urea pretreatment was applied to sugarcane leaves, and its effects on feedstock composition, structural properties, biodegradability, and cocomposting performance were systematically investigated. Under the selected pretreatment conditions (2.5% KOH, 1.5% urea, 80 degrees C, 2 h), the lignin content decreased markedly from 17.09 to 4.67%, while cellulose was largely preserved. This led to a substantial reduction in the lignin-to-cellulose ratio. Structural analyses revealed increased surface roughness and porosity, attenuation of characteristic lignin peaks, and enhanced crystallinity after pretreatment. Prior to composting, the pretreated material was subjected to a 15-day solid-state biodegradation test to evaluate its degradability. The results showed that the degradation rate was 165.5% higher than that of the untreated control. Subsequently, the pretreated sugarcane leaves were co-composted with cattle manure. Compared to conventional composting of untreated leaves under identical conditions, the pretreatment shortened the maturation time by about 50% and increased the total potassium content in the final compost by 63.6%. Furthermore, the pretreatment promoted the conversion of organic matter into humic substances, thereby improving compost stability and maturity. This process ultimately enhanced the nutrient content and agronomic safety of the final product. This study demonstrates that the combined KOH-urea pretreatment is an effective strategy for substantially enhancing the biodegradability of sugarcane leaves, accelerating the composting process, and producing high-quality organic fertilizer. It thus provides a viable pathway for the efficient resource utilization of this agricultural waste.

Promoting the agricultural recycling of biogas slurry (BS) is crucial for sustainable development, yet its long-term ecological impacts remain unclear. Through a multi-year field trial in a sugarcane system, this study examined the effects of BS application (0, 3, and 6 years) on the soil properties, bacterial communities, and functional genes for C, N, P, and S cycling. The results revealed distinct two-phase patterns of changes in soil properties, microbial communities, and functional genes. Short-term (3-year) application induced a “disturbance” phase, characterized by significant acidification (pH decreased by 17.91%), a surge in nitrate-N (increased by 757.27%), and a transient decline in bacterial richness. Long-term (6-year) application drove a “functional restructuring” phase, reversing acidification and significantly increasing soil organic matter (29.05%) and total nitrogen (TN) (20.81%). Bacterial richness recovered, and community composition distinctively restructured. Functional gene analysis revealed shifts in gene abundance that transitioned from high abundance in the short term to a new balance favoring processes like N fixation. Co-occurrence network analysis indicated that this functional shift was associated with core microbial modules (e.g., Firmicutes) and changes in soil pH and SOM. This study suggests that, although short-term application causes significant adjustments, sustained and appropriate BS application can ultimately enhance soil fertility and promote a functionally reorganized state by reshaping microbial interaction networks. It presents a microbial ecological basis for the safe and sustainable use of BS in circular agriculture.

Citrus, a globally significant fruit crop, is predominantly cultivated on sloping land in China with a large amount of resource input and incurs high environmental costs. Current research often relies on general parameters and rarely simultaneously assesses carbon footprint (CF) and water footprint (WF) to reveal the synergistic effects in emission reduction strategies. To address knowledge gaps, we conducted a 2-year county-scale survey and a 3-year field experiment in Zhongxian County, Chongqing, China. We optimized five nutrient management schemes, chemical fertilizer (Che), chemical fertilizer + organic manure (Che+Org), chemical fertilizer + cover crops (Che+CC), chemical fertilizer + organic manure + cover crops (Che+Org+CC), and optimized management (OPT), and analyzed them using the life cycle assessment (LCA) framework. The results showed that OPT achieved dual benefits of high productivity and low carbon-water cost, with a CF reduction of 26.9%-64.6% and a WF reduction of 75.7%-92.1% compared with other treatments. Nitrogen fertilizer production and application were the primary CF sources, whereas cover crop integration markedly decreased WF. A significant positive correlation between CF and grey WF (p < 0.05) indicates that cover crops simultaneously mitigated carbon emissions and reduced nitrogen/phosphorus runoff. While achieving these environmental benefits, the citrus yield of the OPT was 33.57% higher than that of the Che, and the economic returns were 45.51% higher. This study demonstrates that in the sloping land environment, selectively combining organic fertilizers and cover crops can transform the contradiction between yield and the environment into a synergistic effect, thereby deepening the understanding of sustainable nutrient management. The research results show that the OPT system is a superior nutrient management strategy for sloping citrus orchards. The research results also provide reliable and specific evidence to support the optimization of the "organic substitution" policy and offer a feasible approach for low-carbon, high-efficiency citrus production in ecologically fragile regions.

Low soil nitrogen (N) availability in degraded ecosystems intensifies plant-microbe competition and constrains vegetation restoration. As key pioneer species, legumes can enhance soil N availability and potentially alleviate microbial N limitation; however, the underlying mechanisms remain unclear. Here, we investigated microbial N limitation in the presence of eight native legume species differing in nutrient utilization strategies following a 9year natural restoration in a severely degraded karst ecosystem. Four non-legume species served as controls. Plant functional traits and vector-threshold angles of soil extracellular enzymes were measured to characterize plant nutrient utilization strategies and microbial N limitation, while microbial biomass stoichiometric ratios were used to provide complementary information on microbial nutrient status and support the interpretation of microbial N limitation. Soil free-living N fixation and gross N transformation rates were determined using acetylene reduction and 15N isotope labeling techniques, respectively. Our results indicated that four legume species including Lespedeza juncea, Indigofera mengtzeana, Sophora davidii, and Indigofera pseudotinctoria exhibited nutrient-acquisitive traits, whereas other legume species of Dalbergia hupeana, Bauhinia brachycarpa, Bauhinia comosa, and Solanum viciifolia showed nutrient-conservative strategies. Soil microbial growth was predominantly N-limited during early restoration, with considerable interspecific differences among legumes. Microbial N limitation was alleviated in soils associated with nutrient-acquisitive legume species but persisted under nutrientconservative legume species. These differences were closely related to higher rates of free-living N fixation, gross N mineralization, and microbial ammonium immobilization for nutrient-acquisitive legume species. Structural equation modeling further revealed that nutrient-acquisitive legume species alleviated microbial N limitation by enhancing inorganic N supply through increased soil substrate availability, greater abundance and activity of free-living diazotrophs, and altered microbial biomass concentration and composition. Our study indicates that the complementary use of plant traits, soil extracellular enzyme stoichiometry, and microbial biomass stoichiometry may provide a more comprehensive evaluation of soil nutrient availability and limitation. These results

Afforestation has been well documented to enhance soil organic carbon (SOC) pools. However, the capacity of soils to mitigate global warming depends critically on SOC persistence, which is fundamentally governed by the accumulation of non-labile SOC fractions following afforestation. Here, we employed physical fractionation of organic carbon via size/density separation. SOC and its two functionally distinct fractions, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), were quantified in corn-soybean rotation fields and pine plantation forests located in two geological backgrounds: clasolite and limestone areas in southwest Guangxi Province, China. The plantation forests were established in former corn-soybean fields 30-40 years ago. Bulk SOC and MAOC contents in croplands were 74.8% and 86.3% higher, respectively, in limestone areas than in clasolite areas, whereas SOC and its fractions in forests showed no significant differences between the two lithological types. In limestone areas, SOC, POC and MAOC did not differ significantly between croplands and forests, whereas in clasolite areas, these fractions increased by 41.3%, 139.1% and 37.7%, respectively, after afforestation. The proportions of MAOC in croplands constituted 95.7% and 94.0% of bulk SOC in limestone and clasolite areas, respectively, but were reduced by 4.9% and 4.5% following afforestation. These results suggest that afforestation reduces SOC stability by decreasing the proportion of MAOC. Incorporating the effects of afforestation on SOC stability into Earth system models is essential for improving predictions of climate-carbon cycle feedback, particularly given the potential prevalence of our observed pattern.