Objective This study aims to determine the optimal irrigation timing under the single-irrigation mode during the growth period for winter wheat in Hebei Province. Methods Using winter wheat cultivar Jimai 22 as the test material， a field experiment was conducted over two growing seasons （2021-2022 and 2022-2023）. Three irrigation and nitrogen topdressing timing treatments were implemented： at the 4th （T4）， 5th （T5）， and 6th （T6） leaf visible stages in spring. The effects of irrigation and nitrogen topdressing at different timings on wheat water consumption characteristics， dry matter accumulation， grain yield， and its components were analyzed. Results Under the condition of single-irrigation mode during the growth period， the proportion of water consumption sources and the stage-specific distribution of water consumption in wheat were significantly influenced by the climatic year type. Delaying irrigation had no significant effect on soil water storage consumption or total water consumption throughout the entire growth period and during each stage before and after anthesis， and only promoted the utilization of deep soil water in the 2022-2023 growing season with more precipitation. Pre-sowing soil water storage and water use efficiency showed significant positive correlations with grain yield， while total water consumption showed no significant correlation. Therefore， ensuring water supply at critical stages was more important. Spike number was significantly positively correlated with yield， and grain weight per spike was significantly negatively correlated with yield. Delaying irrigation decreased spike number but increased grain weight per spike. The T6 treatment yielded the lowest during both growing seasons， and the fundamental reason for the yield reduction was that the decrease in spike number exceeded the increase in grain weight per spike. In the 2021—2022 growing season with a pre-sowing soil water storage of 655.74 mm， the T5 treatment showed a slight decrease in spike number and achieved the highest yield. In the 2022-2023 growing season with a pre-sowing soil water storage of only 541.24 mm， the T5 treatment showed a larger decrease in spike number， and the T4 treatment achieved the highest yield. Conclusion Under the single-irrigation mode during the growth period for wheat， prioritizing a higher spike number is key to achieving high yield. When pre-sowing soil water storage is greater than 600 mm or spring rainfall is sufficient， the irrigation can be postponed to the 5th leaf visible stage in spring to balance the grain weight. When pre-sowing soil water storage is less than 550 mm or in drought years， the irrigation must be conducted at the 4th leaf visible stage in spring to ensure spike number. The research findings can provide a theoretical basis and technical support for the water-limited and high-yield cultivation of winter wheat in Hebei Province.

Objective This study aims to investigate the effects of water and nitrogen regulation on the emission patterns of NH₃ and N₂O and the nitrogen fertilizer utilization rate in saline-alkali farmland. Methods Sunflower was used as the research subject. Two irrigation gradients were set： T1， mild deficit irrigation （field capacity 65%-75%）， and T2， full irrigation （field capacity 75%-80%）. Four nitrogen application levels were established： N1 （0 kg/hm²）， N2 （150 kg/hm²）， N3 （225 kg/hm²）， and N4 （300 kg/hm²）. By analyzing the effects of different irrigation gradients and nitrogen application levels on NH₃ and N₂O emissions， the pattern characteristics of nitrogen fertilizer utilization， residue， and loss in saline-alkali land were clarified. Results Under the two irrigation conditions， with increasing nitrogen application rate， both the N₂O emission flux and NH₃ volatilization rate significantly increased. Peak emissions under the N4 treatment were 4.4%-21.4% higher than those under N3 and N2. Under the same nitrogen application level， the cumulative NH₃ volatilization and N₂O emissions under the T2 treatment were 10.10%-20.41% and 16.41%-39.77% higher than those under the T1 treatment， respectively. The gaseous nitrogen fertilizer loss rate under the T1 treatment was 7.05%-32.38% lower than that under the T2 treatment. The ¹⁵N isotope tracing results showed that the fate of fertilizer nitrogen followed the pattern： nitrogen fertilizer loss rate > nitrogen fertilizer residual rate > nitrogen fertilizer utilization rate. The residual fertilizer nitrogen was mainly concentrated in the 0-20 cm soil layer， accounting for 46.13%-63.14% of the total residual amount， and gradually decreased with increasing soil layer depth. Under the T1 treatment， the sunflower yield was higher than that under the T2 treatment by 4.12%-12.38%. The nitrogen fertilizer utilization rate under the T1 treatment was 8.46%-14.96% higher than that under the T2 treatment. Among them， the T1-N3 treatment achieved the highest yield and nitrogen fertilizer utilization rate， reaching 2 796.01 kg/hm² and 26.10%， respectively. Additionally， the effects of salinity on the nitrogen transformation process were mainly related to the composition of salt ions， and Na⁺+K⁺ and \mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{-} were positively correlated with the gaseous nitrogen emission rate （r = 0.57-0.86）. Conclusion For severely saline-alkali farmland， under mild deficit irrigation conditions， a nitrogen application level of 225 kg/hm² （T1N3） can effectively reduce nitrogen fertilizer residue and gaseous losses while ensuring nitrogen fertilizer utilization efficiency， representing the optimal water and nitrogen management mode for emission reduction and efficiency improvement.

Objective This study aims to investigate the water transport mechanisms in the root-soil composites of typical landslide-prone areas on the Loess Plateau and its influence on slope stability. Methods A systematic analysis was performed on the variation process of the soil water breakthrough curve within the root zone of the region. By measuring soil physical properties， macropore structural parameters， and root parameters indicators， the key influencing factors of saturated hydraulic conductivity （K_sat） were identified in combination with linear correlation analysis. Furthermore， redundancy analysis （RDA） and variance partitioning analysis （VPA） were applied to quantify the contribution of each influencing factor to the change ratio of outflow velocity （CR_i）， which is a key indicator of the dynamic process. Results 1） Non-capillary porosity （NCP）， macropore area ratio （PAR）， and root surface area density （RSAD） were the main influencing factors of K_sat， with the coefficient of determination （R²） between PAR and K_sat reaching up to 0.99. 2） Soil gradation and macropore parameters overall had a significant effect on the change ratio of outflow velocity （CR _i ） （F=2.67）， explaining 78.05% of the constrained variation based on redundancy analysis. 3） Gradation influenced the variation mechanisms of water flow paths by regulating macropore structure， explaining 34.8% of the variation based on variance partitioning analysis. Conclusion The saturated hydraulic conductivity （K_sat） of root-soil composites on the Loess Plateau is jointly influenced by basic soil physical properties， macropore parameters， and root parameters. It is primarily dominated by non-capillary porosity and macropores ranging from 0.8 mm to 4.0 mm， and is negatively correlated with soil bulk density. Roots improve permeability by promoting pore development. Furthermore， the influence of particle size distribution on saturated hydraulic conductivity （K_sat） exhibits significant variations among soils under different vegetation types. Regarding the change ratio of outflow velocity， the proportions of sand， silt， and clay are the most dominant influencing factors. This study provides a theoretical basis for further understanding the water transport mechanisms in root-soil composites of loess regions and for evaluating slope stability.

Objective To elucidate the pollution characteristics and environmental risks of polycyclic aromatic hydrocarbons （PAHs） in the Dawen River basin. Methods Surface water and sediment samples were collected from 24 sites in the main stream and major tributaries of the basin. The concentration levels， spatial distribution， source contributions， and ecological risks of 16 priority-controlled PAHs were analyzed. Results 1） The concentration of ΣPAHs in the water bodies of the Dawen River basin ranged from 59.05 ng/L to 105.27 ng/L， while that in sediments ranged from 414.90 ng/g to 2 931.17 ng/g. The spatial distribution trend of PAHs in surface water was： Yingwen River > Mouwen River > Daqing River and Dongping Lake > the main stream of Dawen River > Chaiwen River. The spatial distribution trend of PAHs in sediments was： Daqing River and Dongping Lake > Mouwen River > the main stream of Dawen River > Yingwen River > Chaiwen River. 2） Analysis using the Positive Matrix Factorization （PMF） model revealed that the main sources of PAHs in water were biomass combustion， industrial coal combustion， traffic emissions， and petroleum sources. The main sources of PAHs in sediments were petroleum sources， traffic emissions， coal combustion， biomass combustion， and coke sources. 3） Ecological risk assessment indicated that most PAHs in the basin were at a moderate risk level， while Nap and Ant in sediments were at a high-risk level. BaP and DahA were the primary contributors to the toxic risk of PAHs in the Dawen River basin. The results indicated that the Dawen River basin had been contaminated by polycyclic aromatic hydrocarbons （PAHs）， and its ecological risks could not be ignored. Based on the source apportionment results， it is recommended to prioritize the strengthening of emission controls on major contributing sources such as biomass burning， industrial coal combustion， and traffic emissions. Conclusion Future work should integrate the pollution characteristics of the basin， conduct long-term dynamic monitoring and source control strategy evaluation， and provide scientific support for regional water environment management and ecological security.

Objective This study investigates the response characteristics of water storage at gully heads to rainfall in the black soil region of Northeast China， reveals the variation patterns of water storage at gully heads before and after rainfall， and establishes a quantitative prediction method for its changes before and after rainfall. Methods Four gully heads with similar developmental stages and scales in three study areas （Jiusan， Binxian and Jiutai） were selected as research objects. Differences in soil hydraulic parameters， decay coefficients of water storage， and variation patterns of water storage before and after rainfall were investigated through transient water release and imbibition method （TRIM）， numerical fitting， and prediction model construction. Results Obvious hysteresis effects were observed in soil-water characteristic curves （SWCC） of soils at gully heads， with the intensity ranking as gully 1 ≈ gully 2 < gully 3 < gully 4. After rainfall， water storage decayed exponentially over time， showing rapid decline in the initial stage and slower decline in the later stage. The decay coefficient （K_d） of water storage decreased progressively with increasing soil depth. Model simulations showed that water storage changes at 85.7 % of the monitoring sites were best predicted using 1 h maximum rainfall intensity （I_{1 h}） as the rainfall input parameter， whereas 14.3 % of the sites were better simulated using 2 h average maximum continuous rainfall intensity （I_{2 h}） as input. Therefore， in predicting soil water storage changes， I_{1 h} could be selected as the rainfall input parameter for sites with good infiltration performance， such as gully heads or severely eroded sites. However， I_{2 h} should be selected as the rainfall input parameter for sites with poor infiltration performance or strong water redistribution. Conclusion The evolution of water storage at gully heads after rainfall in the black soil region of Northeast China can be effectively characterized using exponential decay patterns and short-duration rainfall indices. The constructed model can accurately and quantitatively predict short-duration water storage changes at gully heads at the event scale， which provides methodological support for prediction and early warning of gully erosion processes.

Objective This study aims to analyze hydrological cycle patterns under different climatic and vegetation conditions and evaluate vegetation water carrying capacity in arid and semi-arid regions using an ecohydrological model. Methods Eagleson′s ecohydrological model was applied to analyze vegetation water carrying capacity and growing-season water budget under different climatic zones and land use types in the study area. Results 1） Eagleson′s model showed good applicability in simulating vegetation water carrying capacity in the study area， with a coefficient of determination （R²） of 0.85. 2） Current vegetation coverage and vegetation water carrying capacity showed obvious regional differences. Fractional vegetation coverages （FVC） values in five core ecological functional zones-water conservation and management area in the Bashang Plateau and hilly mountainous area of northern North China， desertification control area in the Ordos Plateau， desertification control area in the Hunshandake-Horqin sandy land， degraded desert grassland control area in the Ulanqab Plateau， and degraded grassland control area in the Xilin Gol Plateau-Ujimqin Basin-were 0.54， 0.28， 0.36， 0.20， and 0.31， respectively. 3） In the water conservation and management area of the Bashang Plateau and hilly mountainous areas of northern North China， 49.83% of the land area still has potential for increased FVC， whereas the degraded grassland control area in the Xilin Gol Plateau-Ujimqin Basin， vegetation in 82.04% of the land area has reached the upper limit of water carrying capacity. Across the entire region， vegetation interception and transpiration during the growing season accounted for nearly 90% of precipitation， whereas bare-soil evaporation accounted for less than 10%. Vegetation transpiration increased with increasing FVC. Water budget patterns differed markedly among different vegetation types. Conclusion Eagleson′s model shows good performance and can be used to predict vegetation water carrying capacity in arid and semi-arid regions. Vegetation water carrying capacity shows obvious spatial differentiation， and the potential for increasing FVC varies significantly among regions. Shrublands and grasslands show better climatic adaptability in vegetation-hydrology coupling. Climatic differentiation is the fundamental factor driving spatial differentiation of vegetation-hydrology coupling effects. The results provide theoretical reference and data support for determining FVC in ecological restoration.

Objective To clarify the zonal characteristics of litter water-holding capacity in Robinia pseudoacacia forests and their response mechanisms to mixing patterns on the Loess Plateau. Methods Taking R. pseudoacacia forests on the Loess Plateau as the research subject， the litter was collected from a total of 31 sample plots of pure R. pseudoacacia forests （R_p） and mixed R. pseudoacacia forests ［R. pseudoacacia×Platycladus orientalis （R_p×P_o）， R. pseudoacacia×Prunus sibirica （R_p×P_s）， R. pseudoacacia×Pinus tabuliformis （R_p×P_t）］ in the forest zone， forest-steppe zone and steppe zone to study litter water-holding capacity. Results 1） In all three vegetation zones， the maximum water-holding rate of litter in pure R. pseudoacacia forests （R_p） was higher than that in mixed R. pseudoacacia forests. In the steppe zone， R_p was 5.1% higher than R_p×P_t. In the forest-steppe zone， R_p was 5.6%， 5.3%， and 11.4% higher than R_p×P_o， R_p×P_s， and R_p×P_t， respectively. In the forest zone， R_p was 11.6%， 11.5%， and 20.3% higher than R_p×P_o， R_p×P_s， and R_p×P_t， respectively. Among these， R_p was the lowest in the steppe zone （147.88%）， while the values in the forest-steppe zone （180.80%） and forest zone （170.31%） were relatively similar and higher. For R_p×P_t， the value was the highest in the forest-steppe zone （162.28%）， while the values in the steppe zone （140.64%） and forest zone （141.60%） were similar and lower. 2） During the water absorption-evaporation process， the water-holding rate varied with time： it increased logarithmically during the absorption stage and decreased exponentially during the evaporation stage， with both change rates following a power function decay. 3） The effective water interception capacity of R_p and R_p×P_t was positively correlated with mean annual precipitation and mean annual temperature， and the capacity in the steppe zone was abruptly lower than that in the forest-steppe zone and forest zone. Regarding the optimal forest type within each vegetation zone， R_p in the steppe zone （7.17 t/hm²） was the highest， followed by R_p×P_o in the forest-steppe zone （16.27 t/hm²） and R_p×P_t in the forest zone （17.45 t/hm²）. 4） Partial Least Squares Structural Equation Modeling （PLS-SEM） revealed that climate and topography first directly affected vegetation， and then together with vegetation jointly influenced litter water-holding capacity. Topography could also directly affect the water-holding rate. Conclusion The effective interception capacity of litter in R. pseudoacacia forests on the Loess Plateau is positively correlated with precipitation and temperature. The optimal forest types for the steppe， forest-steppe， and forest zones are R_p， R_p×P_o， and R_p×P_t， respectively. The results provide a theoretical basis for optimizing water conservation forests and assessing regional functions.

Objective This study investigates the variation patterns of runoff in glacier-fed inland rivers and their underlying mechanisms under climate warming， aiming to support water security in arid regions of Northwest China. Methods The Keriya River on the northern foot of the Kunlun Mountains was selected as the study object. Based on hydrological and meteorological data from 1961 to 2019， this study systematically assessed runoff variation characteristics and the driving mechanisms of climate change using the Mann-Kendall trend test， Pettitt method for abrupt change detection， wavelet period analysis， and partial correlation analysis. Hydrological regime changes before and after 2016 were compared from the perspective of reservoir construction. Results 1） Runoff of the Keriya River showed a highly significant increasing trend （p<0.001）， jointly regulated by dominant cycles of 28， 18， and 6 years， with no detectable abrupt structural change. 2） The climate in the basin exhibited asymmetric warming characteristics， with the warming rate of minimum temperature （0.055 ℃/year） being 2.2 times that of maximum temperature （0.025 ℃/year）， and precipitation increased following a stable 23-year cycle. 3） Runoff variation followed a "temperature-dominated， precipitation-assisted， lagged response" pattern， with minimum temperature as the core driving factor and showing a 1-year lag effect. 4） After a reservoir was constructed， a preliminary peak-shaving and valley-filling regulatory effect was observed， with the runoff coefficient of variation decreasing by 48.91%. The increase in runoff during the non-flood season was significantly greater than in the flood season. Conclusion Runoff increase of the Keriya River is primarily dominated by snow and glacier melt induced by nighttime warming， and the basin is currently in a gain period of glacial meltwater. Reservoir operation has already produced a peak-shaving and valley-filling regulatory effect on natural hydrological processes， but it has not altered the long-term increasing trend driven by climate. The findings provide a scientific basis for water resources management in alpine inland river basins under climate change.

Objective This study investigates the effects and mechanisms of biochar application on the accumulation of total soil organic carbon （SOC） and key organic carbon fractions such as microbial necromass carbon （MNC） in paddy soils. Methods A field experiment was conducted to analyze the changes in SOC fractions， such as MNC and enzyme activities， five years after a one-time application of maize straw biochar at rates of 20 t/hm² （M20）， 30 t/hm² （M30）， and 40 t/hm² （M40）. Results Compared with the control （no biochar application）， biochar treatments increased the contents of SOC， particulate organic carbon （POC）， and mineral-associated organic carbon （MAOC） by 19.4%-45.0%， 36.3%-65.3%， and 13.4%-47.2%， respectively， whereas dissolved organic carbon （DOC） and microbial biomass carbon （MBC） decreased by 9.8%v29.2%， and 19.5%-29.1%， respectively. Biochar treatments had no significant effects on the contents of biomarkers such as mannosamine， glucosamine， muramic acid， and galactosamine， nor on fungal necromass carbon （FNC） and bacterial necromass carbon （BNC）. However， biochar treatments significantly reduced the contribution rates of FNC， BNC， and MNC to SOC by 16.6%-32.4%， 16.7%-27.2%， and 17.0%-30.8%， respectively. The M30 treatment significantly decreased the activities of polyphenol oxidase （PHOX）， peroxidase （PERO）， α-glucosidase （AG）， β-D-cellobiohydrolase （CB）， and β-xylosidase （XYL） by 19.8%， 24.7%， 32.7%， 34.2%， and 33.7%， respectively. Correlation analysis indicated that the contribution rate of MNC to SOC was significantly negatively correlated with pH， POC， and MAOC， and positively correlated with MBC and some hydrolytic enzyme activities. Random forest model prediction showed that MAOC and pH were the main driving factors determining the contribution of MNC to SOC. Conclusion Biochar application enhances the accumulation and stability of SOC mainly by promoting the accumulation of POC and MAOC rather than MNC. The results provide a theoretical reference for improving soil carbon sequestration in paddy soils through biochar application.

Objective This study aims to investigate the specific mechanisms by which nitrogen application regulates rhizosphere bacterial denitrification pathways in salt-affected farmland， thereby promoting sunflower root growth and yield. Methods Field plot experiments with drip irrigation under plastic mulch were conducted in sunflower farmland from 2023 to 2024. Four nitrogen application levels were set： the local conventional nitrogen application rate as control （CK： 200 kg/hm²）， 25% nitrogen reduction （N1： 150 kg/hm²）， 50% nitrogen reduction （N2： 100 kg/hm²）， and 75% nitrogen reduction （N3： 50 kg/hm²）. Results The two-year experiments demonstrated that moderate nitrogen reduction improved the rhizosphere soil environment in salt-affected farmland and promoted sunflower root growth and yield formation. Compared with CK， both N1 and N2 treatments significantly increased Ca²⁺ （17.22%， 10.56%） and Mg²⁺ （34.75%， 25.40%） contents in rhizosphere soil at the budding stage， and reduced \mathrm{C}{\mathrm{l}}^{-} and \mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}-} contents. Furthermore， N1 treatment significantly promoted oxalic acid and citric acid secretion by root at the budding stage （59.07% and 60.11%）， and N2 treatment significantly promoted formic acid secretion by root at both the budding stage and the maturity stage. Regarding functional genes， N1， N2， and N3 treatments reduced the relative abundance of denitrifying genes narG， nirK， and nirS， whereas N1 treatment increased the abundance of the nosZ gene and altered the composition of nosZ-type bacterial communities， including increasing the relative abundance of nosZ-type Acidobacteria and Proteobacteria. Regarding crop growth and yield formation， N1 and N2 treatments significantly increased root surface area density （RSAD） at the flowering stage and root length density （RLD） at the budding stage. Over two years， N1 treatment significantly increased sunflower 100-seed weight （9.07%）， seed weight per head （9.08%）， and yield （5.05%）. In contrast， N2 and N3 treatments significantly reduced RSAD values （23.66%， 29.46%）， 100-seed weight （21.67%， 29.51%）， and seed weight per head （21.66%， 29.49%） at the maturity stage. Conclusion A 25% nitrogen reduction treatment has a potential inhibitory effect on the initial stage of denitrification （\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}→NO） and a potential promoting effect on the complete denitrification process （N₂O→N₂） in rhizosphere soil. This not only suppresses nitrogen loss from salt-affected farmland at the source but also promotes N₂ reduction_. Meanwhile， it shows significant advantages in promoting plant root growth and yield formation， as well as improving the rhizosphere soil ionic environment. These findings provide a theoretical basis for scientific nitrogen application and nitrogen loss control in the Tumuchuan Plain irrigation district.

Objective This study reveals controlling mechanisms and relative importance of interface roughness， particle gradation， and coupling effects of temperature and thickness on the development of soil desiccation cracking， providing a theoretical basis for preventing engineering hazards such as anti-seepage failure and mechanical instability of soil masses. Methods Sediments from Qingshitan Reservoir in Guilin were selected as test materials， and a series of laboratory drying model tests were designed and conducted covering different particle gradations （intrinsic components）， bottom interface roughness （boundary conditions）， and drying temperatures and initial soil layer thicknesses （environmental and geometric conditions）. High-precision imaging equipment was used to record the whole process of water evaporation and crack evolution in soils. Digital image processing techniques were applied to perform binarization and skeletonization of crack networks to quantitatively extract characteristic parameters such as crack ratio， average crack width， and fractal dimension. Range analysis was employed to systematically calculate and compare the contribution weights of different factors to desiccation cracking development. Results 1） Interface roughness was the primary controlling factor of crack network development and morphological evolution， with a contribution weight of 57.08% to crack ratio. Increased interface roughness significantly enhanced geometric complexity and topological connectivity of crack networks and induced significant curling at soil edges. 2） Particle gradation， acting as an intrinsic factor， had a contribution weight of 26.98%. An increase in fine particle content showed significant positive correlations with crack ratio， crack width， and fractal dimension， fundamentally determining volumetric shrinkage potential and final cracking modes of soils. 3） The combined contribution rate of temperature and thickness was approximately 16.00%. Specifically， the contribution weight of initial layer thickness （9.18%） was significantly higher than that of the drying temperature （6.76%）. The former dominated macroscopic distribution patterns of cracks primarily by constraining the release range of tensile stress， while the latter exhibited relatively complex non-monotonic variation characteristics. Conclusion The dominant factors controlling soil desiccation cracking development are interface roughness and particle gradation， while environmental temperature and initial thickness play secondary synergistic roles. The results provide a scientific basis for the prevention and control of cracking hazards， material improvement， and construction process optimization of anti-seepage soil masses in practical geotechnical engineering.

Objective This study aims to investigate the morphological change process of scour holes at the headcut of ephemeral gullies on slopes with typical herbaceous communities and their main controlling factors. Methods Field runoff scouring experiments were conducted on slopes covered by three typical herbaceous communities in the loess hilly-gully region （Stipa bungeana， Lespedeza davurica， and Artemisia gmelinii）. Close-range photogrammetry was applied to monitor morphological change processes of scour holes. Results 1） Significant differences in root mass density and soil properties were observed among different herbaceous communities. In the topsoil layer （0~0.2 m）， the Artemisia gmelinii community exhibited significantly higher root mass density， root length density， total porosity， saturated water content， and aggregate mean weight diameter than the other two communities， while soil bulk density， cohesion， and penetration resistance showed the opposite pattern. 2） Herbaceous communities significantly affected the morphological characteristics of scour holes and their change processes. Morphological parameters， including width， height， depth， area， volume， shape factor， and depth-to-diameter ratio， showed fluctuating variations with scouring duration， following an increase-decrease-increase trend. Significant differences in morphological development of headcut scour holes at gullies were observed among different herbaceous communities， with the slowest development in the Artemisia gmelinii community， followed by Lespedeza davurica and Stipa bungeana. 3） Pearson correlation and partial least squares （PLS） analyses showed that root mass density， root length density， total porosity， saturated water content， and aggregate mean weight diameter significantly affected scour hole depth. PLS structural equation modeling （PLS-SEM） indicated that vegetation root traits and aggregate mean weight diameter were key factors affecting scour hole depth development， with total effects of -0.65 and -0.53， respectively. Vegetation roots significantly increased soil aggregate stability， thereby inhibiting scour hole development. Conclusion The findings provide important theoretical support for understanding mechanisms by which vegetation restoration influences headward erosion in ephemeral gullies.

Objective Counties are key spatial units for implementing the new-type urbanization and the "dual carbon" strategies， and their spatiotemporal evolution and driving mechanisms of carbon emission efficiency are crucial for addressing the green transformation challenges in resource-based regions. Methods Based on multi-source heterogeneous data from 102 counties in Shanxi Province from 2012 to 2023， this study employed a Super-SBM model with undesirable outputs to measure carbon emission efficiency. It then integrated the Dagum Gini coefficient， exploratory spatiotemporal data analysis （ESTDA）， the XGBoost-SHAP interpretable machine learning model， and panel quantile regression to systematically analyze the spatiotemporal patterns， regional disparities， dynamic transitions， and nonlinear driving mechanisms of carbon emission efficiency. Results 1） Spatiotem-porally， carbon emission efficiency exhibited a stable distribution pattern of "high in the north and south， low in the central" with phased increases， with high-efficiency areas gradually agglomerating in the core zones of urban agglomerations and areas along the Yellow River. 2） Regional disparities primarily originated from inter-group differences and super-variable density， exhibiting a fluctuating process of "divergence-convergence-re-divergence"， with persistent spatial imbalance. 3） Global and local spatial analyses indicated that carbon emission efficiency had significant positive spatial autocorrelation and path dependence. LISA time paths and spatiotemporal transitions revealed that southern and southwestern Shanxi were active zones of local structural changes， showing evident signals of state transitions and restructuring. 4） The driving mechanisms exhibited significant nonlinearity and quantile heterogeneity. Economic density and land use efficiency had positive promoting effects on carbon emission efficiency with threshold effects， while population density and fiscal expenditure intensity generally acted as negative constraints. The positive effects of new-type urbanization and industrial structure upgrading were more pronounced in medium- and high-efficiency counties. Conclusion The study reveals the complex adaptive mechanisms of county-level low-carbon development in resource-based regions. The spatiotemporal heterogeneity and threshold effects of the driving factors indicate that future efforts require the formulation of differentiated and precise emission reduction policies to synergize high-quality county-level development with the "dual carbon" goals.

Objective This study aims to examine whether and how conservation tillage improves the climate adaptability of grain production， revealing its heterogeneous effects from a dual-dimensional perspective of proactive response and passive adaptation. Methods Based on panel data from 44 sample counties in Heilongjiang Province， China， from 2012 to 2022， a dual-dimensional evaluation framework was established incorporating proactive response and passive adaptation. The Tobit models， system generalized method of moments （GMM）， double machine learning， and spatial Durbin models were employed to empirically test the impacts of conservation tillage on climate adaptability. Results 1） From 2012 to 2022， the climate adaptability of grain production in Heilongjiang Province exhibited an overall evolution pattern of first declining and then rising， with 2017 as a key turning point. Spatially， the pattern evolved from a scattered distribution of high-value areas in the early stage to a distinct east-west differentiation， with high-value areas in the east and low-value areas in the west. 2） Conservation tillage had a significantly positive effect on proactive response， but no significant effect on passive adaptation. The system GMM results showed that the first-order lag term of climate adaptability was significantly positive， indicating that the adaptability improvement showed evident path dependence and dynamic accumulation characteristics. Spatial analysis further demonstrated that the direct and indirect effects of conservation tillage on proactive response were 0.119 and 0.711， respectively， with indirect effect playing a dominant role， indicating a significant spatial spillover effect. 3） The effect of conservation tillage on improving proactive response was more pronounced in regions with higher levels of economic development and flatter terrain. Conclusion Conservation tillage can significantly improve the climate adaptability of grain production， mainly by strengthening proactive response， and exhibits evident path dependence and spatial spillover characteristics. The research findings provide a basis for optimizing agricultural climate adaptation policies from a dual-dimensional perspective and for enhancing the resilience of grain production systems.

Objective This study aims to investigate the response status， regional differences， and influencing factors of habitat quality and landscape patterns in the Huaihe River basin and the Haihe River basin， providing theoretical support and a scientific basis for decision-making in the development of differentiated ecological protection strategies for the river basins. Methods Land use data from five periods between 2003 and 2023 were selected. The InVEST model was used to evaluate habitat quality in the river basins， and landscape pattern indices were calculated. The bivariate spatial autocorrelation method was employed to analyze the response relationship and inter-basin differences between the two. Furthermore， the explanatory power of physical geographical factors on the spatial differentiation of habitat quality was explored. Results 1） Cultivated land area decreased significantly in the Huaihe River basin （-20 394.68 km²） and the Haihe River basin （-13 783.16 km²）， while the areas of forest land， water bodies， and construction land all increased. Habitat quality was predominantly at low levels and declined over time， with decreases of 6.48% and 6.55%， respectively. 2） Habitat fragmentation gradually intensified in both river basins， while patch shape complexity remained stable （FRAC_MN fluctuation < 0.003）. Habitat quality in the Huaihe River basin showed a positive correlation with contagion （CONTAG） and prominent negative responses to patch shape complexity and land distribution uniformity. In contrast， habitat quality in the Haihe River basin was mainly negatively affected by the intensification of fragmentation. 3） Topographic factors were the core driving factors of habitat quality changes in the Huaihe River basin （q = 0.295） and the Haihe River basin （q = 0.467）， followed by atmospheric pollution stress （PM_2.5， O₃）， exhibiting spatiotemporal dynamics. The explanatory power of the interactions among natural environmental factors was stronger than that of single factors. Conclusion The evolution of habitat quality in the Huaihe River basin and the Haihe River basin exhibits differentiated characteristics. The heterogeneity of the response mechanisms between habitat quality and landscape patterns in the river basins requires the implementation of zonal governance and targeted restoration strategies to enhance the stability and service functions of regional ecosystems.

Objective This study aims to systematically characterize the overall spatial patterns， regional differentiation， and dynamic evolution of territorial space utilization efficiency within China′s urban agglomerations， and to reveal the role of enhanced efficiency in optimizing resource allocation and spatial structure within these agglomerations. Methods 14 urban agglomerations in China were selected as the research objects. The super-efficiency SBM model and Gini coefficient decomposition were employed to reveal the regional differences and sources of territorial space utilization efficiency. Additionally， kernel density estimation and Markov transition probability matrix were applied to analyze the evolution trends from 2010 to 2022. Results 1） The region as a whole showed a temporal pattern of urban space utilization efficiency > ecological space utilization efficiency > agricultural space utilization efficiency. During the study period， the average efficiency values were 0.645， 0.326， and 0.163， respectively. 2） The overall disparity in the territorial space utilization efficiency among urban agglomerations showed a trend of first decreasing and then increasing， with the Gini coefficient rising from 0.131 in 2010 to 0.145. Moreover， the differences between urban agglomerations were the primary source of the overall disparity. 3） The level of comprehensive territorial space utilization efficiency demonstrated strong spatial spillover effects. Furthermore， the state transition of efficiency levels within each urban agglomeration was more likely driven by the positive effect of high-level neighboring areas. Conclusion Adopting a development model of coordinated and mutual assistance within and outside the region can break the constraints on internal resource allocation and factor circulation. Meanwhile， actively leveraging the spillover effects of high-level urban agglomerations can promote the optimization and enhancement of the territorial space layout of urban agglomerations.

Objective To explore the spatiotemporal evolution patterns and main obstacle factors of cultivated land ecological security in the main grain-producing areas of the Yellow River basin， thereby providing a scientific reference for sustainable cultivated land use and improving ecological security. Methods Based on six-phase panel data from 60 prefecture-level cities in the Yellow River basin， the pressure-state-response （PSR） model was employed to construct an evaluation index system for cultivated land ecological security in the main grain-producing areas of the Yellow River basin. The entropy method and comprehensive index method were used to calculate the comprehensive index of cultivated land ecological security and classify its security level. The obstacle degree model was then used to identify the key obstacle factors affecting cultivated land ecological security. Results 1） The cultivated land ecological security index increased from 0.28 in 2000 to 0.43 in 2023， representing a relatively significant increase. The ecological security level shifted from "relatively unsafe" to "critically safe"， but there remained a considerable gap from the "relatively safe" level， indicating substantial room for future improvement. 2） The level of cultivated land ecological security exhibited significant regional differences. From 2000 to 2015， only three cities had cultivated land ecological security at the "critically safe" level. In 2023， 45 cities had cultivated land ecological security at the "critically safe" level. 3） From the perspective of criteria layers， the obstacle degree of response showed a positive declining trend in Henan， Shandong， Sichuan， and Inner Mongolia. However， the primary obstacle factor in Henan， Shandong， and Sichuan was the obstacle degree of pressure， whereas Inner Mongolia needs to focus on overcoming the obstacle degree of state. 4） Cultivated land area per capita， disposable income of farmers， share of primary industry in GDP， land reclamation rate， and forest coverage were the main obstacle factors affecting cultivated land ecological security. Conclusion Cultivated land ecological security in the main grain-producing areas of the Yellow River Basin shows an overall trend of continuous improvement， but the overall level remains low， and severe challenges persist. The research results can provide strong scientific support for promoting tailored governance and policy implementation in different regions.

Objective This study systematically characterizes the spatial correlation network of new-type urbanization and examines its impact on territorial spatial utilization efficiency， aiming to provide theoretical support and references for improving new-type urbanization policies and promoting the efficient utilization of territorial space. Methods Based on panel data from 21 prefecture-level cities in Guangdong Province from 2005 to 2023， social network analysis was used to characterize the spatial correlation network of new-type urbanization. A super-efficiency model （SBM） was applied to measure territorial spatial utilization efficiency， and a panel data-based fixed effects model was constructed to empirically validate the impact of the spatial correlation network of new-type urbanization on territorial spatial utilization efficiency. Results 1） The spatial correlation network of new-type urbanization in Guangdong Province formed a core-periphery stratification structure， with the Pearl River Delta as the core area and the remaining regions as peripheral areas. 2） The network relevance score remained at 1 throughout the study period， and no island nodes were observed. Network density first increased and then decreased， but overall remained at a relatively low level. Network hierarchy showed a fluctuating declining trend， indicating a transition from a hierarchical structure to a flatter one. Network efficiency first increased and then gradually decreased， while network stability improved. 3） The degree centrality， closeness centrality， and betweenness centrality of Guangzhou， Shenzhen， Foshan， and Zhuhai remained at relatively high levels. 4） The spatial correlation network of new-type urbanization helped improve territorial spatial utilization efficiency. However， this enhancement effect was more pronounced in the Pearl River Delta region， plain areas， and in the dimension of urban spatial utilization efficiency. Conclusion It is necessary to internalize network-based thinking to guide the transformation of new-type urbanization and to encourage cities to formulate differentiated development strategies based on their own resource endowments and functional positions within the spatial correlation network of new-type urbanization， thereby strengthening the role of the network in promoting territorial space efficient utilization.

Objective This study aims to clarify the spatiotemporal evolution patterns， obstacle factors， and cultivated land improvement zoning in the Loess Plateau of northern Shaanxi from 1990 to 2020， and to optimize the regional allocation of cultivated land resources and achieve the strategy of "grain security in the land". Methods Taking Yulin City as the study area， the evaluation indicator system for cultivated land quality mainly covered five aspects： climatic conditions， soil nutrients， cultivated land management， site conditions， and physicochemical properties. The spatial autocorrelation model and the obstacle degree model were introduced to analyze the spatiotemporal evolution characteristics and core restrictive factors of cultivated land quality， and based on this， the improvement zones were scientifically delineated. Results 1） From 1990 to 2020， the cultivated land quality index in Yulin City showed an upward trend （rising from 0.52 to 0.55）， with a spatial distribution pattern of "higher in the east and lower in the west， and higher in the south and lower in the north". 2） The spatial heterogeneity was significant. The high-high-clustering-type cultivated land was distributed in Suide County， Wubu County， and other loess hilly-gully regions， while low-low-clustering-type cultivated land was concentrated in Dingbian County， Jingbian County， and other sandy grassland areas. 3） The diagnosis of obstacle factors indicated that accumulated temperature was the primary factor restricting cultivated land quality in Yulin City. Based on the dominant obstacle factor types， the city was divided into 22 regional types， including accumulated temperature zone， average patch area-pH zone， and organic carbon zone， with differentiated improvement plans proposed for key zones. Conclusion The research findings can provide a scientific basis for cultivated land quality protection and high-quality agricultural development in the northern Shaanxi Loess Plateau.

Objective This study aims to clarify the spatiotemporal evolution characteristics of compound soil erosion in the source region of the Yellow River under the background of ecological restoration and reveal its response mechanisms to climate change. Methods Based on meteorological observations， remote sensing-derived vegetation index， and topographic data from 1980 to 2020， the RUSLE， RWEQ， and freeze-thaw erosion models were coupled to quantitatively assess the intensity of three types of soil erosion driving forces. Transition matrices were employed to analyze the spatiotemporal evolution pathways， while pixel-based partial correlation analysis was conducted to reveal the independent responses of compound erosion to annual precipitation， annual average temperature， and annual average wind speed. Results From 1980 to 2020， the climate in the source region of the Yellow River exhibited a warming and wetting trend， characterized by a significant increase in precipitation， a temperature rise of 1.5 ℃， and a wind speed reduction of 0.3-0.6 m/s， while vegetation coverage increased by more than 40.0%. The intensities of water， wind， and freeze-thaw erosion all decreased significantly. Partial correlation analysis between different climate variables and compound erosion driving forces revealed that， during the study period （1980-2020）， the positive driving effect of precipitation on erosion continuously strengthened （the proportion of positively correlated area increased from 27.4% to 56.0%）， the influence of temperature shifted from promoting to suppressing erosion （the proportion of positively correlated area decreased from 46.0% to 12.8%）， and the driving effect of wind speed markedly weakened （the proportion of positively correlated area decreased to 19.8%）. The alternating and synergistic effects of compound erosion driving forces in the source region of the Yellow River resulted in abnormal responses of climate variables and erosion intensity changes under specific spatiotemporal conditions. Conclusion The ecological restoration project effectively improves the compound soil erosion environmental characteristics in the source region of the Yellow River， thereby suppressing the compound soil erosion in this region. The alternating and synergistic effects of compound erosion driving forces lead to abnormal spatiotemporal responses of climate variables and erosion intensity changes. The research findings provide theoretical references for the intensity assessment of compound soil erosion and its response to environmental changes.

Objective To address the limitations of existing nature relationship index （NRI） in depicting the human-nature relationship at the individual level in ecologically fragile regions， and their inability to identify regional differences and key constraining factors， this study aims to reveal the overall level， spatial differentiation， major obstacles， and intrinsic trade-offs and synergies of farmers′ relationship with nature in northern Shaanxi. Methods Taking NRI as a theoretical reference， the macro human-nature relationship framework was downscaled to the individual farmer level. An indicator system of the farmers′ relationship with nature index （FRNI） was constructed， consisting of three first-level dimensions， six second-level dimensions， and sixteen third-level indicators. Based on 522 household questionnaires conducted in 25 counties/districts of northern Shaanxi form July to August 2025， index measurement， the obstacle degree model， and Spearman correlation analysis were employed to analyze the overall level， spatial pattern， key obstacles， and trade-offs and synergies of farmers′ relationship with nature. Results 1） The average FRNI in northern Shaanxi was 0.53， indicating a moderate overall level. Among the three first-level dimensions， the "nature is safeguarded" dimension scored the highest （0.61）， the "nature is thriving and accessible" dimension ranked in the middle， and the "nature is used with care and respect" dimension scored the lowest （0.46）. This suggested that although government-led ecological governance and environmental protection have established a certain foundation， farmers remained relatively weak in resource conservation， ecological care， and active participation. 2） The FRNI in northern Shaanxi showed an overall spatial pattern of "higher in the south and lower in the north"， with different dimensions showing differentiated spatial structures. This indicated that regional differences in farmers′ relationships with nature resulted from the combined effects of natural endowment， agricultural production practices， ecological governance efforts， and farmers′ livelihood structures. 3） The main obstacles to improving FRNI were concentrated in limited accessibility to nature， weak water-saving behaviors， and insufficient farmer participation. Overall， relationships among the indicators were dominated by synergies， with a few indicators showing significant trade-offs. Based on obstacle identification and analysis of trade-offs and synergies， a systematic improvement pathway was proposed， which is prioritizing key obstacles， mitigating major trade-offs， and amplifying synergies. Conclusion The perception-based FRNI effectively characterizes the overall status， spatial differences， and key shortcomings of farmers′ relationships with nature in ecologically fragile regions. In northern Shaanxi， improving farmers' relationship with nature depends not only on ecological improvement， but also on the coordinated enhancement of accessibility to nature， water-saving behavior， and farmer participation， with targeted governance tailored to local conditions. The findings provide a support for evaluating farmer-nature relationships， diagnosing critical obstacles， and informing policy in the Loess Plateau and similar ecologically fragile regions.

Objective This study aims to analyze the impact of spatiotemporal changes in land use patterns on regional carbon storage in Heilongjiang Province， predict future evolution under multiple scenarios， and quantitatively identify the main driving factors of spatial differentiation in carbon storage. Methods Based on four periods of land use data in Heilongjiang Province from 1990 to 2020， the PLUS-InVEST-Geodetector model was coupled to analyze changes in land use patterns and their carbon effects. Future land use and carbon storage in 2060 were simulated under four scenarios： Natural development， cultivated land protection， ecological protection， and urban development. Results From 1990 to 2020， carbon storage in Heilongjiang Province showed a net decrease of 53.46×10⁷ t， with a spatial pattern of high in central regions and low in surrounding areas， high in the north and low in the south， and high in mountainous areas and low in plains. The conversion of forest land to cultivated land， grassland， and unused land was the primary pathway for carbon loss. Multi-scenario simulations indicated that carbon storage in 2060 followed the order： ecological protection scenario （2 012.71×10⁷ t） > natural development scenario （2 000.59×10⁷ t） > urban development scenario （1 996.01×10⁷ t） > cultivated land conservation scenario （1 992.08×10⁷ t）. Geodetector analysis revealed that the spatial differentiation of carbon storage was mainly influenced by factors such as elevation， distance to water bodies， and normalized difference vegetation index （NDVI）. Interactions among factors were mainly characterized by two-factor enhancement and nonlinear enhancement， with the strongest interactions observed between digital elevation model （DEM） and annual precipitation， DEM and distance to rivers， population density and DEM， and DEM and NDVI. Conclusion During the historical period， the conversion of forest land to cultivated land and grassland in Heilongjiang Province led to a continuous net decrease in carbon storage. Future projections indicate that carbon storage is the highest under the ecological protection scenario， with factor interactions centered on DEM dominating the spatial differentiation of carbon storage. Therefore， it is necessary to control the conversion of land types with higher carbon density to those with lower carbon density， strictly implement black soil protection policies， and adopt ecological protection measures. The impacts of natural and socio-economic factors should be comprehensively considered when formulating regional ecological protection and economic development policies， so as to promote the sustainable development of the regional economy in Heilongjiang Province.

Objective This study aims to scientifically delineate land use functional zones in Anhui Province， identify the key driving factors of landscape ecological risk， and reveal the spatiotemporal evolution characteristics and spatial conflict patterns of ecological risk， providing scientific support for regional ecological security and territorial space planning. Methods Taking Anhui Province as the study area， a land use functional zoning scheme was developed by integrating the morphological spatial pattern analysis （MSPA）， Conefor， and minimum cumulative resistance （MCR） models and applying the resistance threshold method. On this basis， This study combines the XGBoost model with the SHAP interpretation method to quantitatively analyze the effects of topographic conditions， climatic factors， and socio-economic factors on landscape ecological risks. Results 1）According to land use functions， Anhui Province can be divided into three core areas， among which the ecological protection core area accounts for 30.96%， the agricultural production core area accounts for 35.52%， and the construction and development core area accounts for 33.52%. Spatially， the three areas are respectively concentrated in the southern Anhui region， the northern Anhui region， and the urban agglomeration in central Anhui. 2） From 2000 to 2020， the overall landscape ecological risk in the region has been continuously intensifying， with the proportion of areas with high and very high risks increasing from 16.95% to 32.81%. In terms of spatial distribution， low-risk zones largely coincided with ecological protection zones， while high-risk zones were concentrated in construction development zones. 3） The analysis of influencing factors showed that topographic factors exerted the greatest influence on the provincial risk pattern. Climatic factors were the dominant factors in ecological protection and construction development zones， whereas socio-economic factors had the most significant influence on risk in agricultural production zones. 4） Ecological risk conflicts within the province were significant， with relatively high- and high-conflict zones accounting for 30.78%， mainly distributed in cities such as Anqing and Hefei. Conclusion Landscape ecological risk in Anhui Province shows an intensifying trend. The province is influenced by topographic factors， while different zones are driven by climatic and socio-economic factors， and high-risk zones are concentrated in construction development core zones. It is recommended to implement differentiated management strategies based on functional zoning， focusing on mitigating spatial conflicts in areas such as Anqing and Hefei to improve regional ecological security. The findings provide a scientific basis for the synergistic governance of territorial space planning and ecological risk.

Objective To clarify the newly introduced pollution fingerprints during a single hydrological regulation cycle in the Three Gorges Reservoir Area， and accurately identify the sources and driving mechanisms of heavy metals under different hydrodynamic conditions. Methods In the typical riparian water-level fluctuation zones （Shibaozhai， Guojiaba， and Xiangxi River） in the middle and lower reaches of the Three Gorges Reservoir Area， intact net-deposited sediments across a complete hydrological cycle were collected using in-situ sediment columns. The potential ecological risk index （PERI）， canonical correspondence analysis （CCA）， and positive matrix factorization （PMF） were applied to systematically analyze the pollution characteristics， sources， and environmental driving mechanisms of heavy metals （As， Cd， Cr， Cu， Mn， Ni， Pb， Zn）. Results 1） Pollution characteristics： Cd was the primary pollution factor， with its average content significantly higher than the background value of the reservoir area. The ecological risk level in the reservoir center was significantly higher than that in the reservoir head， and the high-risk hotspots were concentrated in the deep flooding zone （145~155 m）. 2） Driving mechanisms： Flooding duration explained 54.5% of the variance in heavy metals， serving as the primary driving factor. The "hydraulic sorting effect" driven by long-term flooding facilitated the preferential adsorption and accumulation of fine particles and heavy metals in low-elevation areas. 3） Source apportionment： The PMF model identified three pollution sources， namely traffic/industrial sources （mainly contributing to Cd and Pb）， agricultural/mixed sources （mainly contributing to As， Cu， and Ni）， and natural sources （mainly contributing to Mn）. Among these， the contribution rate of industrial sources to Cd was nearly 100%. Conclusion It is confirmed that the net-deposited sediments can effectively retrace short-term pollution inputs in the reservoir area and confirm the interception effect of the midstream backwater fluctuation zone as a "sediment filter" and its vertical enrichment mechanism， thereby providing a scientific basis for the refined management and zoned prevention and control of heavy metal pollution in the water-level fluctuation zone of the Three Gorges Reservoir Area.

Objective This study aims to investigate the interactive effects of plastic film mulching and combined soil amendments on the soil quality index （SQI） and maize yield， in order to achieve the synergistic improvement of soil quality and maize yield in the dryland farming systems of Northwest China. Methods A three-factor randomized block design was adopted， including two mulching methods： no mulching （M0） and black plastic film mulching （M1）， two application rates of water-retaining agent （W0： 0 kg/hm²； W1： 45 kg/hm²）， and three application rates of biochar （B0： 0 t/hm²； B15： 15 t/hm²； B30： 30 t/hm²）. The effects of different treatment combinations on soil physicochemical properties， SQI， and maize yield were compared. Results 1） Both mulching and amendments improved soil physical structure. The W1B30 treatment reduced the bulk density in the 0-40 cm soil layer by an average of 4.29% and increased porosity， field water capacity， and saturated water content. Mulching provided a more stable hydrothermal background for the amendments to function， resulting in more pronounced improvements in surface structure and water-holding capacity. 2） The improvement in soil chemical properties was mainly attributed to biochar. In the 0-20 cm soil layer， soil organic carbon （SOC） in the W1B30 treatment increased by 23.73% compared to the control， while available phosphorus and available potassium increased by 22.66% and 9.86%， respectively. The extent of improvement in SOC and nutrient availability by amendments differed under different mulching conditions， indicating that mulching methods regulated the response of C and N accumulation and available nutrients to amendments. 3） The combined application of plastic film mulching and amendments jointly promoted maize yield， and the yield was more sensitive to mulching×amendment interactions. Under the no mulching condition， W1B30 increased yield by 19.25%， while with mulching， W1B15 increased yield by 18.61%. SQI showed a significant positive correlation with yield （R² =0.67）， and the SQI of the W1B30 treatment increased by 138.95%. Conclusion Plastic film mulching significantly increases maize yield. The combined application of amendments markedly improves the physical structure of dryland farmland soil， enhances water and nutrient retention， thereby increasing soil fertility and achieving synchronous improvement of soil quality and yield. This study provides a basis for optimizing mulching management and amendment application in dryland regions， and for advancing sustainable production with reduced or no plastic film.

Objective This study aims to reveal the differences in infiltration processes of soda saline-alkali soils with different degrees and their influencing factors， and to evaluate the applicability of different infiltration models in simulating the infiltration process of soda saline-alkali soils. Methods Using the one-dimensional vertical constant-head single-ring infiltration method， field in-situ infiltration experiments were conducted to study the characteristics of infiltration process parameters in soda saline-alkali soils with different degrees， analyze the effects of salinization-alkalization indicators on the infiltration process， and evaluate the applicability of different prediction models. Results 1） As pH increased from 9.31 to 10.35， exchangeable sodium percent （ESP） rose from 1.09% to 65.82%， and sodium adsorption ratio （SAR） increased from 1.24 to 115.71， the stable infiltration rates of the five tested soils decreased by 41.81% to 99.59% compared with the initial infiltration rates. Among them， the Suaeda salsa land with the highest degree of salinization and alkalization showed the largest decrease， with a stable infiltration rate of only 0.13 mm/h. 2） Correlation analysis indicated that the stable infiltration rate was significantly negatively correlated with ESP and pH （p<0.01）， and significantly negatively correlated with exchangeable Na⁺ （p<0.05）. The average infiltration rate was significantly negatively correlated with ESP， exchangeable Na⁺， SAR， pH， and salt content at different levels. 3） Based on the coefficient of determination （R²） of the models and the correlation with the saline-alkali indicators of soda saline-alkali soils with different degrees， the simulation performance of the Horton infiltration model was superior to that of the general empirical model when SAR<108.60， salt content （SC）<10 568.64 mg/kg， and electrical conductivity （EC）<1.70 mS/cm. When the degree of salinization and alkalization exceeded this range， the general empirical model performed better. Conclusion The degree of soda salinization and alkalization is a key factor constraining soil infiltration capacity. The applicability of infiltration models for soils with different degrees of salinization and alkalization can be optimized based on thresholds of typical saline-alkali indicators. These findings provide a theoretical basis and methodological support for simulating water movement and managing irrigation and drainage in soda saline-alkali soil regions.

Objective This study aims to construct a gully erosion susceptibility assessment model in order to provide an important scientific basis for early warning of gully erosion occurrence and its precise management in the black soil region of Northeast China. Methods Kedong County in Heilongjiang Province， a typical thick-layer black soil region， was selected as the study area. Erosion gullies were extracted based on 0.4 m high-resolution remote sensing images. Redundant variables were eliminated using the variance inflation factor （VIF）. Four machine learning models covering linear， nonlinear， and ensemble learning architectures-logistic regression （LR）， support vector machine （SVM）， random forest （RF）， and extreme gradient boosting （XGBoost）-were compared. The SHAP （Shapley Additive exPlanations） interpretability model was introduced to quantify the contribution of each influencing factor to gully erosion susceptibility. Results 1） XGBoost demonstrated the best predictive capability for gully erosion susceptibility （training set AUC=0.81， test set AUC=0.75）， followed by the SVM and RF （test set AUC=0.74）， while LR showed the weakest predictive capability （AUC=0.67）. 2） The gully erosion susceptibility predicted by the four models all exhibited a spatial distribution pattern of "low in the periphery and high in the center" at the county scale， but there were significant differences in the susceptibility levels. The RF model predicted the largest proportion of high gully erosion susceptibility， accounting for 45.0%. The gully erosion susceptibility predicted by the SVM and XGBoost models in the study area was predominantly moderate and very low levels， accounting for 56.2% and 59.2%， respectively. In contrast， the LR prediction results indicated that low gully erosion susceptibility was dominant， covering 39.4% of the study area. 3） SHAP analysis revealed that the digital elevation model （DEM） was the dominant factor influencing gully erosion susceptibility （SHAP value=0.55）， exhibiting a significant positive effect. The stream power index （SPI） had the second strongest positive driving effect on gully erosion susceptibility （SHAP value=0.30）， while the normalized difference vegetation index （NDVI） showed a clear negative effect on gully erosion susceptibility （SHAP value=0.37）. Conclusion In the thick-layer black soil region of Kedong County， significant differences are observed in the gully erosion susceptibility levels evaluated by the four machine learning models. The integration of the XGBoost model with the SHAP method enhances the interpretability of machine learning models in predicting gully erosion susceptibility. Moreover， gully erosion susceptibility is jointly driven by the coupled effects of "terrain-dominated control， vegetation regulation， and confluence hydrodynamics triggering". These findings deepen the understanding of gully erosion occurrence and provide theoretical guidance for optimizing gully erosion control measures in black soil regions.

Objective This study systematically evaluates the estimation accuracy of a simple rainfall erosivity model across different regions and rainfall levels. Methods Based on observational data from 2 078 meteorological stations in humid， semi-humid， and semi-arid regions of China， rainfall erosivity of different magnitudes was calculated using the classic EI₃₀ model at hourly and daily rainfall scales as the baseline， and then compared with estimates from the daily rainfall erosivity model proposed. Results 1） Rainfall erosivity calculated by the two methods showed a spatial pattern of low values in the northwest and high values in the southeast， with significant positive correlations in humid， semi-humid， and semi-arid regions. 2） Without considering rainfall classification， estimation deviations of the daily rainfall erosivity model in humid， semi-humid， and semi-arid regions were 16.06%， 22.47% and 24.19%， respectively. However， under different rainfall levels， deviations of rainfall erosivity estimation in the above regions increased markedly， with systematic overestimation for moderate and heavy rain and systematic underestimation for rainstorms and extreme rainstorms. 3） Considering both data deviation and correlation coefficient， the daily rainfall erosivity model achieved the highest estimation accuracy in humid regions under rainstorm conditions， followed by semi-humid regions under rainstorm， and the lowest accuracy was found in humid regions under moderate rainfall conditions. Conclusion Accuracy differences and variation patterns of the daily rainfall erosivity model under different rainfall levels and in different dry and wet regions will provide an important basis for development of zoned and graded estimation models.

Objective This study aims to quantify the spatiotemporal evolution of ecosystem service functions in the Horqin sandy land， providing a scientific basis and theoretical support for environmental management and ecological restoration. Methods Based on land use data from three recent periods （2000， 2010， and 2020）， the InVEST model was used to quantitatively evaluate five key ecosystem service indicators in the Horqin sandy land， including annual water yield， water quality purification （phosphorus load）， soil conservation， carbon storage， and habitat quality. The ecosystem service index was calculated. Results 1） Ecological land （grassland and forest land） and construction land increased over the periods， while cultivated land， unused land， and water areas decreased continuously. 2） Annual water yield increased over the periods， with the mean value rising from 131.19 mm to 266.39 mm. Highvalue areas （300.00~400.00 mm） in the western region expanded significantly， and the spatial distribution across the region shifted from lowvalue dominance to concentration in highgradient zones （>200.00 mm）. 3） The overall water purification capacity showed a declining trend， with the average value decreasing from 1.31 kg/km² to 1.22 kg/km². Highvalue areas in the eastern region contracted generally，accompanied by weakened spatial heterogeneity. 4） Soil conservation and carbon storage were influenced by vegetation distribution and elevation， showing a pattern of high values at high elevations and low values at low elevations. The mean soil conservation increased from 27.72 t/km² to 60.38 t/km²， while the mean value of carbon storage remained stable from 143.41 t/km² to 144.86 t/km². Highvalue areas （≥80.00 t/km²） continued to expand. 5） Habitat quality improved over the periods， with the mean value increasing from 0.28 to 0.30， while spatial heterogeneity remained stable. 6） The ecosystem service index increased with the expansion of ecological land， while fragmentation in lowvalue areas （<0.20） intensified. Conclusion Expansion of forest-grassland has significantly improved ecosystem service functions in the Horqin sandy land， increasing annual water yield and reducing phosphorus load， while promoting coordinated enhancement of soil conservation and carbon storage. This provides a scientific basis for achieving ecological restoration in the arid and semi-arid regions of northern China.

Objective This study aims to investigate the spatiotemporal evolution characteristics and driving factors of soil conservation in the Three Gorges Reservoir area. Methods Taking Wanzhou， a representative county in the Three Gorges Reservoir area， as a case study， multi-source remote sensing data from 1990 to 2020 were used. The InVEST model was applied to assess the spatial differentiation characteristics of soil conservation function， and the Geodetector model was employed to analyze the driving mechanisms of its evolution. The influence of slope on soil conservation in sloping cropland and corresponding regulation measures were also explored. Results 1） From 1990 to 2020， soil conservation function in Wanzhou exhibited a trend of increase followed by decrease， with a spatial pattern of higher values in the east and lower values in the west. Land use types were mainly sloping cropland and forest land. 2） Soil conservation function in Wanzhou demonstrated significant spatial clustering characteristics， with low-low clustering areas expanding from the north to the southwest， and high-high clustering areas concentrated in the eastern region. Kernel density high-value areas were consistently located in the central region， and kernel density values showed a fluctuating decrease followed by an increase. 3） Natural environmental factors were the primary drivers of spatial differentiation in soil conservation function. Slope （q=0.71） was the dominant factor， followed by vegetation coverage （q=0.43） and soil type （q=0.24）. Interactions among all factors showed enhancement effects， among which combinations such as slope and temperature， and slope and vegetation coverage， exhibited the strongest effects （q>0.75）. 4） Soil conservation function in sloping cropland was closely related to slope. On slopes from 3° to 8°， soil conservation function remained stable ［from 120.64 t/（hm²·a） to 379.35 t/（hm²·a）］. On slopes from 8° to 25°， it was at a moderate level ［from 61.17 t/（hm²·a） to 81.93 t/（hm²·a）］. Differentiated management measures could be adopted for different slope gradients： low-slope areas should adopt straw mulching and contour ridge tillage， medium-slope areas should combine engineering and vegetation measures， and slopes >25° should prioritize conversion of cropland to forest and grassland. Conclusion The results provide a scientific basis for soil erosion control and ecological restoration in the Three Gorges Reservoir area.

Objective This study aims to reveal the spatiotemporal differentiation patterns of cultivated land landscape from the provincial scale to economic zones in Sichuan Province， and to quantify the contributions and interactive effects of natural and socio-economic factors on landscape pattern changes. Methods Based on multi-source remote sensing and geographic information system （GIS） technology， a spatiotemporal evolution model of landscape ecology was constructed on the ArcGIS and Fragstats platforms. Combined with the geodetector and entropy weight-TOPSIS method， the spatial heterogeneity characteristics and driving mechanisms of cultivated land landscape patterns in Sichuan Province and its five major economic zones from 2000 to 2022 were systematically analyzed. Results 1） From 2000 to 2022， the cultivated land in Sichuan Province generally showed a trend of scale reduction， fragmentation intensification， and connectivity decline. The area of dryland decreased by 13 961.0 km²， with a higher reduction rate than that of paddy fields. The number of patches increased sharply， and landscape dominance continued to weaken. 2） The five major economic zones exhibited significant differences. The Chengdu Plain Economic Zone showed quantity reduction and shape fragmentation. The Western Sichuan Economic Zone presented paddy field expansion and dryland shrinkage. Both paddy fields and dryland in the Northeast Sichuan Economic Zone decreased by more than 19%. The area of dryland in the Southern Sichuan Economic Zone decreased by 11.58%， with local retention of core cultivated areas. The area of dryland in the Panxi Economic Zone decreased by 27.49%， with the highest degree of fragmentation. 3） In terms of driving mechanisms， the interactions between natural and socio-economic factors were dominated by two-factor enhancement and nonlinear enhancement effects. Among them， population density had the highest interactive explanatory power （0.97）. The influence of human-driven factors generally increased across regions. Economically developed areas were mainly driven by urbanization and industrialization， ecologically sensitive areas were dominated by natural constraints and policy regulation， and traditional agricultural areas were trapped in a cycle of agricultural decline and population loss. Conclusion The findings of this study can provide a theoretical basis for the construction of an ecological security pattern for cultivated land and differentiated management strategies in Sichuan Province， thereby supporting the sustainable use of cultivated land landscapes and the process of territorial spatial governance.

Objective This study aims to investigate the spatiotemporal evolution characteristics and coupling relationship between landscape patterns and ecological surplus in the Kuye River basin， thereby providing guidance for ecological restoration and sustainable development in this region. Methods Taking the Kuye River basin as the study area， land use data were obtained based on six periods of Landsat remote sensing images from 2000 to 2024 using support vector machine classification and visual interpretation， and multiscale landscape pattern indices were extracted. Using statistical yearbook data from 2000， 2010， and 2024， ecological surplus was calculated based on ecological footprint and ecological carrying capacity models， and the relationship between landscape patterns and ecological surplus was quantified using Spearman rank correlation analysis. Results 1） From 2000 to 2010， under the influence of high-intensity industrial and mining development and land use expansion， landscape fragmentation in the river basin significantly intensified， with patch density （PD） and division index （DIVISION） increasing markedly. After 2010， driven by policies such as the Grain for Green Program and mine ecological restoration， contagion （CONTAG） and cohesion （COHESION） exhibited increasing trends， indicating a transition of landscape patterns from fragmentation towards overall structural optimization. 2） Changes in ecological surplus were mainly driven by the rapid growth of the energy footprint. Specifically， the ecological deficit of fossil energy land expanded from 1.376 1×10⁶ hm² in 2000 to 9.28×0⁷ hm² in 2024， accounting for an overwhelming proportion of the total ecological deficit and becoming the key factor constraining the decline of ecological carrying capacity in the river basin. 3） Significant correlations were observed between landscape pattern indices and ecological surplus. CONTAG and COHESION showed extremely significant positive correlations with ecological surplus （p<0.01）， while patch density （PD）， diversity index （DIVISION）， and Shannon's diversity index （SHDI） exhibited significant negative correlations. The "fragmentation and disturbance-driven diversity" under industrial and mining disturbance exerted a significant inhibitory effect on ecological surplus. Conclusion Landscape fragmentation is the core factor regulating ecological surplus in the Kuye River Basin， and the turning point in 2010 is directly associated with regional industrial and mining regulation policies. Restoration measures that reduce landscape fragmentation and enhance the connectivity of ecological land can effectively promote the steady recovery of ecological surplus in the river basin. The findings can provide a quantitative reference for ecological restoration planning in industrial and mining-affected river basins of the Pisha sandstone region.