Abstract:[Objective] To explore the differences of vegetation growth characteristics between different plant communities and gully positions. [Methods] The vegetation growth characteristics of 5 typical plant communities were systematically studied in Zhifanggou small watershed of Ansai, Shaanxi Province.The investigated characteristics included species diversity, coverage, aboveground biomass, litter storage and underground biomass. [Results] (1) The above ground biomass, litter storage and root reduction coefficient were significantly affected by vegetation type, tree cutting ditch > shrub cutting ditch > herb cutting ditch, and the coverage was shrub cutting ditch > herb cutting ditch > tree cutting ditch. (2) The species diversity index and coverage of the right side of gully (sunny to semi-sunny slopes) were smaller than those on the left side (shade to semi-shade slopes); (3) Under the comprehensive influence of hydrothermal conditions, there was no obvious difference in vegetation growth characteristics between gully bottom and the original slope; (4) The accumulation of litter on the original slope was greater than that of different positions of gully. [Conclusion] The research results provide data foundation and theoretical support for understanding of the potential effects of vegetation restoration on the development of gully and evaluating the role of vegetation in mitigating gully erosion.

Abstract:[Objective] To understand the variations in soil erodibility and nutrient content caused by different slope positions and land uses, and to discuss the influence of various factors on soil erodibility and nutrient status. [Methods] Soil and root samples were collected, and the Comprehensive Soil Erodibility Index (CSEI) and Comprehensive Soil Nutrient Index (CSNI) were calculated using a weighted sum method under different slope positions and land uses. [Results] (1) There were differences in both CSEI and CSNI among different slope positions. The highest value of CSEI was recorded on the slope crest (0.653) and the lowest value was at the bottom of the slope (0.275), while the highest value of CSNI was found on the slope crest (0.715) and the lowest value was at the top of the slope (0.341). (2) Differences in both CSEI and CSNI were observed among different land uses. The highest value of CSEI was observed in fallow land (0.617) and the lowest value was in forests (0.252), while the highest value of CSNI was found in forests (0.793) and the lowest value was in fallow land (0.322). (3) CSEI was significantly negatively correlated with clay content, sand content, root length density and aboveground biomass. It was also significantly positively correlated with silt content and soil bulk density. Soil bulk density had the greatest direct impact (0.26). CSNI was significantly positively correlated with clay content, sand content, root length density and aboveground biomass. It was also significantly negatively correlated with silt content and soil bulk density. Clay content had the greatest direct impact (0.45). There was a significant negative correlation between CSEI and CSNI. [Conclusion] Slope position significantly influences both CSEI and CSNI, emphasizing the importance of focusing on slope crests and mid-slopes in vegetation restoration efforts. Vegetation restoration in various geomorphic positions effectively reduces CSEI and enhances CSNI, with trees being more effective in controlling soil erosion.

Abstract:[Objective] The impact of soil erosion on nutrient content and stoichiometric ratios in soil is crucial for further comprehending and effective control of quality degradation in the sloping farmlands of black soil regions. [Methods] Selecting straight slopes cultivated for over a century and a convex slope cultivated for more than five decades in the typical black soil area of Keshan County as the research objects, utilizing ¹³⁷Cs tracing method to estimate soil erosion rates on the slopes. Quantitative analysis was conducted on the relationship between soil erosion and key parameters such as soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, along with the stoichiometric ratio in the ecological chemistry. [Results] (1) Using ¹³⁷Cs tracing technique, the average annual erosion rate of the whole slope was 4 428.56 t/(km²·a), the average erosion rates of the linear and convex slopes were 3 284.53,5 884.59 t/(km²·a), and the total erosion volumes were calculated at 3.21×10⁵,2.94×10⁵ t/km², respectively. (2) The overall carbon/nitrogen ratio (C/N) on the slopes showed a highly significant positive correlation with SOC (p<0.01), and the carbon/phosphorus ratio (C/P) correlated positively and significantly with SOC (p<0.01). Conversely, the nitrogen/phosphorus ratio (N/P) demonstrated a highly significant negative correlation with TP (p<0.01). On linear slopes, SOC, TN, C/N, C/P and N/P were significantly lower than those on convex slopes (p<0.01), while TP content was higher than that on convex slopes (p<0.01). (3) The spatial distribution characteristics of soil erosion on the slopes align with the distribution of SOC, TN and TP. The amount of soil erosion on the slopes exhibited a highly significant negative correlation with SOC, TN, TP and C/P (p<0.01), and a significant negative correlation with C/N (p<0.05). The correlation with N/P is negative, though not statistically significant (p>0.05). [Conclusion] Ultimately, soil erosion redistributed SOC, TN and TP on the slopes, affecting the stoichiometric ratios of soil nutrients and leading to substantial nutrient loss on the slopes.

Abstract:[Objective] The objective is to explore the spatial and temporal changes of soil erosion and its main controlling factors in the Longchuan River Basin, as well as to understand mastering the local soil and water , which is conducive to building an ecological barrier in the upper reaches of the Yangtze River. [Methods] The temporal and spatial variation characteristics of soil erosion in the Longchuan River Basin during 2000 to 2020 were studied using the revised universal soil loss equation (RUSLE) combined with GIS and RS technology. Additionally, the optimal parameters-based geographical detector (OPGD) model was used to quantify the influence and interaction of driving factors on the temporal and spatial dynamic changes of soil erosion in the Longchuan River Basin. [Results] (1) Soil erosion in the Longchuan River Basin was mainly slight and moderate erosion. In 2000, the proportion of slight and moderate erosion was 49.17%. In 2010, the total proportion was 50.29%; In 2020, the total proportion is 59.29%. There was little change in soil erosion from 2000 to 2010, but from 2010 to 2020, a total of 9.01% of areas experiencing soil erosion transitioned from moderate to slight or mild levels. (2) The results of the OPGD showed that the land use type had the strongest explanatory power for the temporal and spatial dynamic changes of soil erosion in the study area, with a q value was 0.18. The interaction between land use type and slope had the strongest explanatory power for soil erosion in Longchuan River Basin, with a q value reached 0.45. [Conclusion] Soil erosion in the Longchuan River Basin is mainly slight and mild, with an overall improving trend, but there are still areas with strong soil erosion. Land use type has the strongest impact on soil erosion in the basin, with woodlands and meadows being the most important types covering 67.02% of the total area in the study area. In the future, we should focus on regional changes in vegetation coverage, continue to promote ecological protection policies, and be alert to the risk of soil erosion in complex terrain areas.

Abstract:[Objective] Wind-water erosion crisscross region in Loess Plateau is a typical fragile ecosystem. Biological soil crusts (BSCs) are widely distributed in this region and play key roles in the accumulation and transformation of soil organic carbon (SOC). However, the effect of BSCs succession and microorganisms on enzymes related to organic carbon conversion is still unclear.[Methods] In this manuscript, SOC contents, microbial number and enzymes related with carbon conversion in different BSCs types were investigated. The relationships among SOC, microbial number and enzume activities related with carbon conversion were also analyzed by SEM model.[Results] (1) BSCs succession significantly inceased SOC content and enzyme activities related with carbon conversion. SOC and enzyme activities in BSCs layer(0—2 cm) were significantly higher than those in bare sand 2—5 cm soil layer (p<0.05). (2) The number of bacteria, fungi and actinomyces in moss crusts was the highest, and the number of fungi and actinomyces significantly increases with BSCs succession. Bacteria and fungi in the BSCs were significantly higher than those in 2-5 cm soil layer. However, actinomycetes in BSCs (except moss crusts) were lower than 2-5 cm layer. (3) SEM model indicated that SOC, enzyme activities and microbial number showed significant correlation. [Conclusion] The accumulation of SOC by BSCs succession provided a rich substrate and nutrients for enzymes related with carbon conversion and microbes,which were helpful for the increase of microbes and improvement of enzyme activities related with carbon conversion. Microbes play critical roles in driving enzyme activities related with carbon conversion and maintaining carbon balance in BSCs.

Abstract:[Objective] The summer rainfall intensity in the desert steppe is strong and concentrated, and the harm of hydraulic erosion is serious. It is of great significance for soil and water conservation in this area to clarify the process of runoff and sediment yield, as well as the law of nutrient transport. [Methods] The experiment is based on natural rainfall observation data and artificial rainfall simulation methods, studying the runoff and sediment production processes, nutrient transport patterns in the desert steppe area, and investigating the impact of vegetation on runoff and sediment production through different vegetation treatments. [Results] (1) Different vegetation treatments had different effects on soil and water conservation. Among the three different treatments, the soil and water conservation effect of natural grassland the best, and the runoff reduction rate and sediment reduction rate were 11.37% and 49.67%, respectively. (2) The process of runoff and sediment production would change the material composition of surface soil, make the surface soil coarse-grained, and also affect soil nutrients. After rainfall, the sand content increased by 5.97%~15.71%, and the soil available N, P and organic matter decreased by 40.84% , 27.08%, 33.49%, respectively. (3) The runoff and sediment yield increased with the increase of slope and rainfall intensity, and the power function can better fit the relationship between rainfall duration and runoff and sediment yield. With the increase of rainfall intensity, the peak runoff yield increased by 6.70 L on average when the slope was 5°~25°. When the rainfall intensity is 0.6~2.0 mm/L, the inflection point of the sediment yield increase rate will appear between the slope of 15°~20°. [Conclusion] The research results can provide a theoretical reference for the comprehensive prevention and control of soil and water loss in desert steppe areas, which is helpful in improving the ecological environment of desert steppe regions and carrying out soil and water conservation efforts in this area.

Abstract:[Objective] Soil respiration occupies an important proportion in the annual total soil respiration during freeze-thaw process. The effects of water content, freezing temperature and freeze-thaw cycles on soil carbon mineralization dynamics during soil freeze-thaw process were studied. [Methods] The study focuses on chernozem soil from the Nenjiang County Heshan Farm Jiusan Soil and Water Experimental Station in Heilongjiang Province, China was used as the research object to carry out an indoor freeze-thaw degree simulation test. Seven freeze-thaw cycles were carried out, and three soil moisture content were set 100% field water holding capacity (100% WHC), 60% field water holding capacity (60% WHC), and 30% field water holding capacity (30% WHC). Additionally, three environmental temperatures were used a constant 10 °C (control), -5 °C (mild freezing) and -15 °C (severe freezing). [Results] The number of freeze-thaw cycles, moisture content and freezing temperature had significant effects on CO₂ emissions and the impact degrees were -0.63, 0.21 and 0.14, respectively. The thawing process notably increased soil carbon mineralization. The soil carbon mineralization of 60% WHC in the first three freeze-thaw cycles increased 33.0% and 35.2%, respectively, compared with 100% WHC and 30% WHC in the last 4 freeze-thaw cycles. In the case of severe freezing, the carbon mineralization of 100% WHC soil in the first 2 freeze-thaw cycles increased by 25.2% and 68.0% respectively, compared with 60% WHC and 30% WHC soil in the last 5 freeze-thaw cycles. [Conclusion] The number of freeze-thaw cycles had the greatest effect on soil CO₂ emission, followed by moisture content, and the least freezing temperature. The freeze-thaw effect increased the cumulative CO₂ emissions of soil with low water content. The cumulative CO₂ emission of soil with high water content was reduced. For soils with medium moisture content, mild freezing increased CO₂ cumulative emissions, while severe freezing decreased them. The first-order kinetic equation fitted the CO₂ emissions from freeze-thaw soil well (R² > 0.997), both moisture content and freezing temperature significantly influenced the potential for organic carbon mineralization (C₀ value).

Abstract:[Objective] Researches on the effects of freeze-thaw action on slope soil erosion in the Chinese typical Mollisol Region can deepen the understanding of the mechanism of slope erosion process and provide important scientific basis for slope erosion control.[Methods] Using snowmelt, wind and rainfall erosion driven by a single erosion forces as controls, the effects of freeze-thaw on snowmelt, wind and rainfall erosion were analyzed by designing simulation experiments of freeze-thaw-snowmelt, freeze-thaw-wind and freeze-thaw-rainfall in the typical Mollisol Region of China. The experiment treatment consisted one freeze-thaw action, two snowmelt runoff flows (1 and 2 L/min), one wind velocity (12 m/s), one rainfall intensity (100 mm/h) and one slope (3°). [Results] (1) The freeze-thaw effect significantly increased the amount of slope snow melt, wind and rainfall erosion (p<0.05). Compared with no freeze-thaw action, the snowmelt erosion under 1,2 L/min snowmelt runoff increased by 2 042.9% and 777.9%, and the wind and rainfall erosion increased by 118.0% and 74.9%, respectively. (2) The effect of freeze-thaw on the process of water erosion (snowmelt and rainfall erosion) was greater than that on the process of runoff, and the process of slope erosion is aggravated, which increased the duration of active period and the intensity of slope erosion. The freeze-thaw action also increased the sediment transport height of wind erosion by 30%, and the sediment transport amount of wind erosion at each height increased by more than 50%. (3) The freeze-thaw action reduced soil erosion resistance, which significantly reduced surface soil bulk density, soil shear strength and soil hardness by 2.5%, 22.6% and 15.0%, respectively. At the same time, the freeze-thaw effect increased the average flow velocity 13.6%~25.0%, the shear force by 2.3%~81.9%, and the resistance coefficient by 1.6 %~20.6%, thus aggravating the slope erosion process. [Conclusion] Freeze-thaw action changed the relationship between erosive dynamics and resistance, and intensified the process of snowmelt, wind and rainfall erosion on slope.

Abstract:[Objective] Soil and water conservation is important in protecting and improving the ecological environment, which plays an important role for the sustainable development of ecosystems. [Methods] While the study of the soil and water conservation effectiveness in regional scale provide an effective theoretical basis for soil and water conservation. [Results] We supposed an estimation method for the regional-scale soil and water conservation rates by remote sensing based on the RUSLE (revised universal soil loss equation), and estimated its the spatial pattern in Shanxi Province.The results showed that the soil erosion in Shanxi Province is dominated by moderate erosion, with an area of about 49 545.68 km², and the soil and water conservation rates is 68.38% in 2022, and the soil and water conservation rates accounted for the largest proportion in high level. The soil and water conservation rates of natural vegetation is higher than that of cropland, among which, the rates of forest is the highest at 84.37%. The soil and water conservation rates of the natural vegetation and cropland accounted for the largest proportion in high level with 48.11% and 46.46%, respectively. The rates is greatly affected by slopes, and showed a trend of significant decrease followed by gentle fluctuation. Compared with previous researches, the estimated spatial pattern of soil erosion in Shanxi Province were consistent with the existing data. And the estimated soil and water conservation rates was significantly correlated with the published targets. [Conclusion] The method of estimating soil and water conservation rates at the regional scale by remote sensing can provide an important theoretical and methodological basis for evaluating the effectiveness and impact of soil and water conservation ecological projects and other national large-scale ecological projects.

Abstract:[Objective] To analyze the scale-dependent relationships between daily sediment yield and key environmental factors and to explore effective prediction method to cope with the prediction challenges caused by the complexity of sediment transport mechanisms and the nonlinearity of hydrological processes. [Methods] Employing the Composite Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) approach, we analyzed the multi-temporal scale variability characteristics between daily sediment yield and five potential influencing variables (flow rate, precipitation, average temperature, potential evapotranspiration, and NDVI) in the controled regions of four hydrological stations in the Fu River basin of Southwest China from 2013 to 2018. Interactions between daily sediment yield and related variables at different temporal scales were identified, upon which predictions of daily sediment yield were predicted. [Results] The CEEMDAN method successfully decomposed the daily sediment yield and its potential influencing variables into 10-11 intrinsic mode functions (IMFs) and residual item, revealing the significant changes of the daily sediment yield at different temporal scales ranging from 3 to 730 days. After decomposition, daily sediment yield showed significantly enhanced correlation with howrate and precipitation across all temporal scales, whereas temperature, potential evapotranspiration, and NDVI were primarily significantly correlated with long-term scale sediment yields. By using stepwise multiple linear regression to predict the daily sediment yield , the prediction performance of the model is significant, and the R² values exceeds 0.55 at all stations. [Conclusion] The CEEMDAN method effectively revealed the scale dependency between sediment yield and its influencing variables, offering a new perspective for understanding the dynamics of river sediment transport.

Abstract:[Objective] In order to clarify the law of sediment yield and sediment loss of different land use types under different rainfall types, and to evaluate the benefit of sediment reduction of different land use types under different rainfall types. [Methods] Based on the monitoring data of runoff and soil loss under natural rainfall conditions over 2015—2016 in 31 runoff plots located in the Loess Plateau of China the characteristics of sediment yield and loss in different land use types, including farmlands, abandoned lands, artificial grasslands, natural grasslands, shrublands and artificial forest lands were discussed. The efficiency of runoff and sediment reduction for each land use type under different rainfall types was determined. [Results] The runoff and soil loss of abandoned lands were the largest (30 mm, 86 t/hm²) and artificial forest lands were the smallest (8 mm, 24 t/hm²) under the annual rainfall scale, and there was no significant difference between other land use types. Through the application of duster analysis a total of 120 rainfall events were categorized into three distinct rainfall types based on criteria that included amount, duration, and maximum intensity of rainfall in a 30-minute period. That is, Rainfall Type I: characterised by moderate rainfall duration (749 min), moderate rainfall volume (35.4 mm), and moderate rainfall intensity (16.9 mm/h); Rainfall Type II: comprising short-duration rainfall (222 min), moderate rainfall volume (25.2 mm), and intense rainfall intensity (23.8 mm/h); Rainfall Type III: involving a long duration of rainfall (1 451 min), substantial rainfall volume (40.6 mm), but low intensity of rainfall (11.5 mm/h). When considering the impact of these types of rainfall within the given scale, the study observed the following trends, for the runoff coefficient, exhibiting Rainfall Type II > Rainfall Type III > Rainfall Type I, while for soil loss, exhibiting Rainfall Type II > Rainfall Type I > Rainfall Type III. The runoff coefficient of Rainfall Type I was significantly higher than that of other land use types, reaching 17.7%, which was 2.36 times that of artificial forest land. There were no significant difference in runoff coefficient under Rainfall Type II, and the average runoff coefficient was 19.9%. The runoff coefficient of abandoned lands, artificial grasslands, natural grasslands, and farmlands (average of 14.3%) was significantly higher than that of shrublands and artificial forest lands (averaging at 9.0%). The soil loss of famlands, artificial grasslands, shmblands and artificial forest lands under Rainfall Type II (3.94, 0.87, 1.06, 1.08 t/hm²) > Rainfall Type I (1.60, 0.60, 0.59, 0.63 t/hm²) > Rainfall Type III (0.09, 0.20, 0.06, 0.04 t/hm²). [Conclusion] In the Loess Plateau, the artificial forest land was the first choice to control soil and water loss effectively under the condition of medium-low rainfall intensity and medium-long duration rainfall, and the soil and water conservation effect of shrubland and grassland was better under short-duration heavy rainfall.

Abstract:[Objective] The effects of exposed rocks on the runoff, sediment yield, and hydrodynamic characteristics of slope land needs further study. [Methods] Through the laboratory simulation test, the slope lands with different rock exposure rates (0, 10%, 30%, 50%, 70%) were set, and the artificial simulation rainfall test under different rainfall intensities (30, 60, 90 mm/h) was carried out, in order to explore the impact of rainfall intensity and exposed rocks on runoff, sediment yield and hydrodynamic characteristics of slope land. [Results] The surface runoff and sediment yield of slope land increased with the increased of rainfall intensity, and decreased with the increase of rock exposure rate. Under varying rainfall intensities, the runoff and sediment yield of slopes with 0 and 10% rock exposure rates slope land were not significantly difference in most cases (p>0.05), but the slope with a 0 rock exposure rate was significantly difference from other slopes with rock exposure (p<0.05). There was a significant difference in runoff and sediment yield between lands with low rock exposure rates (10%) and lands with high rock exposure rate (50% or more) (p<0.05). Flow velocity (V), Flow depth (h), Reynolds number (Re), Froude number (Fr), Water flow shear stress (τ) and Flow power (w) increased with the increased of rainfall intensity, the Friction coefficient (f) decreased with the increase of rainfall intensity. The Flow velocity (V), and Froude number (Fr) decreased with the increased of rock exposure rate, while the Flow depth (h) and Friction coefficient (f) increased with the increase of rock exposure rate, and the change regulation of Reynolds number (Re), Water flow shear stress (τ) and Flow power (w) were disparate in different rainfall intensity. Moreover, there were certain differences in hydrodynamic parameters among different slope lands. The quantitative relationship between sediment yield and hydrodynamic parameters was best fitted by Exponential function, Flow velocity (V), (R²=0.819, p<0.05), Water flow shear stress (τ)(R²=0.858, p<0.05) and Flow power (w) (R²=0.890, p<0.05) had better prediction effects on sediment yield of slope land, and Flow power (w) was the best prediction parameter. [Conclusion] The development of this study has further enriched the theory of soil erosion in karst areas, and can provide reference for the establishment of water erosion prediction model suitable for exposed rock slope land.

Abstract:[Objective] To investigate the soil infiltration characteristics of different agroforestry composite modes and their influencing factors types in the purple soil area. [Methods] We analyzed the changes in the soil physical properties and infiltration processes under four agroforestry types in the purple soil area, namely, no crop (CK), peanut (HS), pepper (HJ), and peanut + pepper (HS + HJ), through field surveys and laboratory experiments, and evaluated the applicability of three soil infiltration models including Kostiakov, Horton, and Philip. [Results] (1) The total soil porosity in HJ was not significantly different from that in CK and HS + HJ, but was considerably higher than that in HS (p<0.05); the soil shear strength in CK was similar to that in HS, but were both significantly higher than that of HJ and HS+HJ (p<0.05); the soil bulk density, water content, temperature, water repellency, compactness, and soil hardness were also significantly different among the four agroforestry types (p<0.05). (2) The soil water infiltration process varied significantly among the four types, showing the steady infiltration stage around 20 min under CK and HS, while around 70 and 80 min under HJ and HS + HJ, respectively. The steady infiltration in the HS + HJ was 162%, 140% and 82% higher than that in CK, HS, and HJ, respectively (p<0.05). (3) Compared with the Horton and Philip models, the Kostiakov model was the most effective in fitting the infiltration process (coefficient of determination R²=0.933~0.991), while the Horton model fitted relatively poorly (R²=0.849~0.979). (4) The correlation and multiple linear regression analyses found that the total soil porosity and soil shear strength were the key factors affecting soil infiltration. [Conclusion] The results of the study provide scientific basis for the optimal selection of agroforestry types in the purple soil area.

Abstract:[Objective] The weathering intensity of granite red soil profile is closely related to the formation of Benggang, which promotes the development and expansion of Benggang. Studying the mechanism of weathering intensity and physicochemical properties on Benggang can provide a theoretical basis for the scientific prevention and control of granite Benggang. [Methods] The typical Benggang profile of granite red soil areas was selected as the research object, the oxide content and physicochemical properties of different soil layers were measured, and the influence of weathering intensity on the physicochemical properties of granite red soil was analyzed. [Results] (1) The major element oxides in the soil profile were mainly composed of SiO₂, Al₂O₃ and Fe₂O₃. The weathering crust of granite showed the process of desilication and iron-rich aluminization. The weathering intensity decreased with the increase in the depth of the soil profile, which was in the stage of high weathering. (2) The physical and chemical properties of the soil profile exhibited heterogeneous. The surface layer was characterized by high organic matter, cation exchange capacity, clay content and saturated hydraulic conductivity, with strong cohesiveness and water holding capacity; whereas the lower layer had high sand content, loose structure and strong water permeability. (3) The results of correlation and path analysis indicated that weathering intensity was positively correlated with non-capillary porosity, organic matter, cation exchange capacity, clay content, saturated hydraulic conductivity and boundary water content. Fe₂O₃ had the strongest comprehensive determinative ability for clay content, sand content and boundary water content. (4) The surface weathering intensity was high, with a high proportion of clay, strong water adsorption capacity, strong cementation between soil particles, and good soil stability. The lower layer had a low of weathering intensity, with low content of cementing materials and boundary water content, poor soil corrosion resistance. When the soil was exposed or subjected to water erosion, it easily collapsed, forming Benggang. [Conclusion] The weathering intensity of soil profile has an impact on the physicochemical properties, which is an important factor to promote the formation of Benggang.

Abstract:[Objective] Rainfall erosivity serves as an indicator to assess the potential impact of rainfall on soil erosion, playing a crucial role in evaluating regional soil erosion risk. Therefore, analyzing the temporal and spatial variations of rainfall erosivity in Beijing from 1981 to 2020 holds significant importance for scientifically assessing and preventing regional soil erosion risks. [Methods] This study employed Kriging interpolation, Mann-Kendall non-parametric test, and wavelet analysis based on daily precipitation data collected from 119 rainfall stations in Beijing and its surrounding areas between 1981 and 2020. These methods were utilized to analyze the spatial distribution, trend changes, and periodic fluctuations of annual rainfall erosivity as well as erosivity associated with moderate rain (10~25 mm), heavy rain (25~50 mm), and extreme rain (≥50 mm) in Beijing. [Results] The annual rainfall erosivity in Beijing ranged from 1 691.51 to 3 914.89 (MJ·mm)/(hm²·h·a) during the period from 1991 to 2020. The spatial distribution characteristics of annual rainfall erosivity exhibited similarities with heavy rain and rainstorm but differed from moderate rain patterns. Overall, there was a decreasing trend observed from northeast regions towards the surrounding areas. Over the past four decades, moderate rainfall erosivity demonstrated a significant increasing trend in Beijing; however, no significant mutations or trends were observed for annual rainfall erosivity, heavy rain events, rainstorms or July-August summer precipitation erosivity. Notably large decreasing trends were identified for annual rainfall erosivity within local areas such as Miyun and Pinggu districts. The main cycle for both annual rainfall erosivity and medium-to-heavy intensity precipitation lasted approximately twenty-five years with two to three alternating "low-high" changes. [Conclusion] The study can offer a scientific foundation for soil and water conservation, agricultural practices, and ecological preservation in Beijing.

Abstract:[Objective] Due to the hidden nature of seepage erosion occurring in engineering and the complexity of its development, discrete element simulation has become an important tool for scholars to carry out research on seepage erosion mechanisms.The parametric construction of the solid model influences the transport and loss of particles under water flow by controlling the filling and distribution of particles within the model, and is a key component in carrying out discrete elemental simulations of seepage erosion. [Methods] The current research on discrete element model parameters is mainly a single-parameter discussion. In this paper, from the three dimensions of soil pore space, soil particles and wall sidewalls, six sets of soil models are constructed by considering the changes of porosity, particle overlap ratio and wall modulus, and upward seepage calculations are carried out to record the internal particle loss process, the structural change of the force chain, and the change of the porosity process, in order to evaluate the influence of the three parameters on the model. The influence mechanism of the discrete element model parameters on the seepage and erosion process was also analyzed from a fine-grained point of view. [Results] Discrete element model parameters affect the stage of particle loss under water flow by influencing the composition of particles and force chains within the model. Initial porosity controls the number of particles filling the interior of the model; wall modulus and particle overlap ratio affect the number of contacts within the model. Models with a high number of particles and contacts have internal particles that tend to move as clusters of particles; conversely, free fine particles that do not form contacts undergo longitudinal migration as single particles within the model, and the porosity profile shows fluctuating changes. [Conclusion] In this study, the effect of parameters on the model is described from a fine-grained point of view, with a view to providing a theoretical reference for the use of discrete element simulation methods based on the fluid-structure coupling theory.

Abstract:[Objective] The Qinghai-Tibetan Plateau is an important ecological barrier in China, and alpine meadows are an important part of it, and the function of soil and water conservation is an important ecological service function of alpine meadows. Therefore, it is of great significance to carry out the study of soil erosion process in alpine meadows on the Tibetan Plateau to reduce anthropogenic disturbance of soil erosion and to safeguard the ecological security of the southwest region. [Methods] In this study, five different types of slopes, namely, undegraded, mildly degraded, moderately degraded, bare slopes and artificially restored slopes in alpine meadows of the Tibetan Plateau, were selected to analyze the process of flow and sand production on degraded and restored slopes under different rainfall intensities, and to reveal the relationship between the erosion mechanism and water-sand relationship between degraded slopes and restored slopes with artificial vegetation through the simulated rainfall test in the field. [Results] (1) The initial flow production time is relatively short on the undegraded slopes of alpine meadows and the restored slopes with artificial vegetation because of their dense root system, and the water infiltration ability is relatively weak; while on the mildly degraded slopes, the lateral flow and vertical infiltration ability are relatively strong, and the initial flow production time is relatively long. (2) Under regular rainfall conditions (30 and 60 mm/h), the flow rate of mildly degraded slopes is the smallest, and the flow reduction benefit is the highest, reaching 77.13%, the flow rate of artificially restored slopes is close to that of undegraded slopes and is slightly higher than that of mildly degraded slopes; the cumulative flow rate of bare soil slopes is the largest, and it is significantly higher than other slopes; the flow rate of undegraded slopes under extreme rainfall conditions (90 mm/h) is surging, only lower than that of bare slopes and significantly higher than other slopes. Under extreme rainfall conditions (90 mm/h), the flow rate of undegraded slopes increased, which was only lower than that of bare slopes and significantly higher than that of artificially restored slopes. (3) Under regular rainfall conditions (30 and 60 mm/h), the sand reduction benefit of the artificially restored vegetated slopes was the highest, reaching 81.97% and 89.82%, followed by the undegraded slopes, and with the increase of the degradation degree of the vegetation, the sand reduction benefit was gradually reduced; however, under extreme rainfall conditions, the sand reduction benefit of the artificially restored vegetation and the undegraded slopes was almost the same, and the sand production of the moderately degraded slopes was higher than the undegraded slopes, which is significantly higher than the other slopes. However, under extreme rainfall conditions, the sand reduction benefits of artificially restored vegetation and undegraded slopes are almost the same, while the sand production of moderately degraded slopes is 4.59 times of that of undegraded slopes. [Conclusion] The results of these studies can provide important scientific basis for vegetation restoration and ecological security in alpine meadow area.

Abstract:[Objective] To delve deeper into the spatiotemporal characteristics and pivotal driving factors underlying the hardness of black soil in eroded sloping farmlands. [Methods] Based on the dynamic monitoring of soil penetration resistance across 110 sample points in typical water erosion sloping farmlands, coupled with measurements of pertinent factors, the factors affecting soil penetration resistance were analyzed by multivariate linear regression (MLR) and random forest (RFR) models, and its transfer function was further construct. [Results] The spatiotemporal variability of soil penetration resistance was influenced by a combination of soil depth, moisture conditions, and agricultural practices. Notably, the spatial heterogeneity was significantly lower in the topsoil layer compared to the sub-surface layer, with coefficients of variation of 17.4% and 26.3%, respectively. As the soil dried out and the duration since the last tillage increases, spatial heterogeneity tended to intensify. Soil erosion played a significant role, with higher soil penetration resistance observed in areas of intense erosion compared to deposition zones, particularly under wet conditions where the difference is most pronounced (p<0.05). Furthermore, 73% of the sampled points in the studied sloping farmlands exhibited increased soil penetration resistance compared to natural forestlands, especially in regions of intense erosion. Key factors that influenced soil penetration resistance included soil moisture content, bulk density, and soil organic carbon (SOC), with Pearson coefficients of -0.69, 0.58 and -0.54, respectively, collectively explaining 88% of its variability. In terms of predictive soil penetration resistance, the RFR model demonstrated superior accuracy compared to the MLR model, achieving an R² of 0.91 and an RMSE of 91.2 kPa for mean predictions across the growing season. [Conclusion] This study enhances our understanding of the spatial heterogeneity characteristics of black soil hardness under erosion, providing a theoretical foundation for effective management of soil compaction in black soil regions.

Abstract:[Objective] The engineering disturbances have triggered soil erosion events in subalpine meadows, intensify regional soil erosion and vegetation destruction. The relationship between physical and chemical properties and disintegration characteristics of subalpine meadow soils in central Yunnan was studied to provide reference for soil and water conservation and control and vegetation protection in sub-alpine meadow ecosystems. [Methods] By X-ray diffraction, electron microscopy scanning, and static water disintegration experiments were conducted to determine the physico-chemical properties, mineral composition, microscopic structure, and disintegration characteristics of subalpine meadow soils in central Yunnan. The correlation between soil disintegration and physico-chemical properties was analyzed to explore the reason of soil disintegration in sub-alpine meadows of central Yunnan. [Results] (1) The subalpine meadow soils in central Yunnan exhibited a high susceptibility to disintegration when encountering water. The resistance to disintegration of different parent materials in the same soil layer were as follows sandstone>limestone≈basalt. The characteristics of different soil layers in the same parent material were as follows leaching horizon>deposition layer>parent material layer. (2) Correlation analysis showed that the average soil disintegration rate was significantly negative correlated with organic matter (r=-0.84) and total nitrogen (r=-0.83), positively correlated with clay content (r=0.88), and positively correlated with montmorillonite (r=0.68) and hematite (r=0.77). (3) The main factors affecting the disintegration of subalpine meadow soils in central Yunnan were biological processes and swelling of hydrophilic clay minerals such as montmorillonite and illite. [Conclusion] The resistance to disintegration of subalpine meadow soils in central Yunnan was ranked as follows: Sandstone>limestone≈basalt for different parent materials, and leaching horizon>deposition layer>parent material layer for different soil layers. The subalpine meadow soil in central Yunnan was easy to disintegrate when exposed to water, the main factors affecting the disintegration of subalpine meadow soils in central Yunnan were biological processes and swelling of hydrophilic clay minerals such as montmorillonite and illite.

Abstract:[Objective] As the most active component in forest soil, dissolved organic matter (DOM) can not only be directly utilized by microorganisms, but also be the main carrier for the migration of C, N, P and other elements in the ecosystem. The migration process is influenced by the hydraulic interactions and dissolving processes driven by throughfall. [Methods] Using soil column microcosm in situ culture to analyze the effects of forest throughfall on the dynamics of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP) across varying layers of sandy red soil during the rainy season. The study focused on a subtropical evergreen broad-leaved forest with rainfall as a control. [Results] (1) During the rainfall season, the DOM input of throughfall into soil increased significantly compared with rainfall(p<0.01). The concentrations of DOC, DON and DOP increased by 37.00%, 93.47%, and 85.12%, respectively, and the fluxes of DOC, DON and DOP also increased by 20.76%, 49.93%, and 61.55%, respectively. However, there was no significant difference in output fluxes after passing through the 40 cm deep soil, indicating a strong capacity of the soil to absorb DOM from throughfall. (2) Compared to rainfall, throughfall reduced the C/N and C/P ratios of the soil surface by 29.19% and 26.00%, respectively, without significantly affecting N/P ratios. After passing through 40 cm of soil, throughfall reduced the input C/N, C/P and N/P ratios of the soil by 19.35%, 13.35% and 7.45%, respectively. The increase in DOM in throughfall was mainly due to the absorption of DON and DOP in the canopy, while the decrease in soil DOM was mainly concentrated in DOC and DOP. (3) Soil DOC and DOP showed a reduction in interception, while DON showed an increase in enrichment. Throughfall increased the interception of DOC and DOP in the 0-40 cm soil by 39.93% and 72.42%, respectively, and significantly reduced the release of DON by 32.37%. [Conclusion] These results demonstrate that throughfall in a subtropical evergreen broad-leaved forest can promote the input of DOM and facilitate its uptake at different soil depths, with implications for the sustainable management of ecosystems.

Abstract:[Objective] The aim of this study is to reveal the spatiotemporal patterns of soil organic carbon (SOC) content in terraced fields on the Loess Plateau and investigate the spatiotemporal distribution characteristics of soil carbon sequestration in these terraced fields. [Methods] Using the META analysis method, the variations characteristics of SOC content in terraced soil with soil depth and years of terraced construction were studied, and analyzed the spatiotemporal distribution features of soil carbon sequestration in terraced fields across different regions of the Loess Plateau. [Results] (1) SOC content and carbon sequeering benefits decreased with the increase of soil depth, SOC content in the 80-100 cm soil layer was 60.74% of that in 0-20 cm soil layer, carbon sequeering benefit in the 0-20 cm layer was 23.1% and that in 80-100 cm soil layer was 5.7%. (2) The carbon sequestration benefits of terrace increased nonlinearly with the construction years. The carbon sequestration benefits of 0-20 cm soil layer of terrace gradually increased from -8.29% in the first year of construction to 34% in the 24th year, and then remained stable. (3) During 1979 to 2023, the total carbon sequestration of terraces on the Loess Plateau was approximately 38.29 Mt C, and the average carbon sequestration was 38.49 t C/(km²·a). The Jinghe River upper and middle reaches exhibited the highest average sequestration rate at 50.14 t C/(km²·a), while the Helong interval showed the lowest at 29.04 t C/(km²·a). [Conclusion] Terraced field construction on the Loess Plateau can enhance SOC content, and terraced field carbon sequestration was a relatively lengthy process that requires scientific design and management to maximize its carbon sequestration benefits. Conducting terraced field construction, along with proper planning, design, and scientific management, proved to be an effective measure to enhance regional soil carbon sequestration benefits. The research findings can offer theoretical and methodological support for assessing the carbon sequestration benefits of soil and water conservation in the Loess Plateau region.

Abstract:[Objective] Clarifying the temporal and spatial dynamics and drivers of China’s agriculture net carbon sink provides a theoretical basis for promoting low-carbon development in the agricultural. [Methods] Based on the 19 types of the major carbon sources form four including of rice cultivation, agricultural land use, agricultural materials, and livestock breeding, and 7 types of carbon sinks, this study calculated the agricultural net carbon sink in China and its 31 provinces and cities (excluding Hong Kong, Macau, and Taiwan) from 2002 to 2022, using Arc GIS statistical software analyze temporal and spatial dynamics of agricultural net carbon sink, and using the LMDI model to analyze the drivers agricultural net carbon sink. [Results] The primary source of carbon emissions from agriculture had shifted from enteric fermentation and manure management in the livestock sector to agricultural materials in the plantation sector. Carbon sinks were dominated by the contribution of rice and maize. Overall, there has been fluctuating upward trends in both levels of agricultural net carbon sinks and carbon sinks. There was a spatial distribution pattern with high levels observed in northeast China while low levels were found in western regions. Furthermore, there was a significant positive correlation between net agricultural carbon sinks which exhibited features of high-high or low-low aggregation. Moreover, there was an increasing trend in spatial aggregation. Agricultural net carbon sink could be restrained by factors such as the intensity of the agricultural net carbon sink, the structure of the agricultural industry and the size of the rural population; however, it can be enhanced by economic development. [Conclusion] China’s agriculture showed a positive trend regarding net carbon sinks. Optimizing its industry structure along with improving production methods are crucial for promoting low-carbon development and achieving a sustainable cycle.

Abstract:[Objective] Investigating the interactive coupling characteristics of the PEE system can provide theoretical support and quantitative basis for the ecological advancement of urban areas in the Three Gorges Reservoir Area. [Methods] Based on a comprehensive evaluation of the PEE system in the Three Gorges Reservoir Area from 2000 to 2020, this study utilized the coupling coordination degree model, gravity model, and obstacle degree model to empirically investigate the spatiotemporal evolution characteristics, spatial connectivity features, and main obstacle factors of the system’s coupling coordination degree. [Results] (1) The comprehensive development level of the PEE system in the reservoir area had shown a gradual increase from 2000 to 2020. (2) During the study period, the coupling and coordination degree of the system was basically unchanged, with a not very high level of coordination. The type of coordination showed the spatial characteristics of "Southwest-Northeast" and "Central-North", with an overall benign upward development trend. (3) The spatial correlation of the coupling and coordination degree of the system in neighboring regions had a significant positive autocorrelation, the total spatial linkage was rising in general, the spatial linkage strength was weak, and it was gradually weakening with the increase of the geographic distance. (4) The influence of each factor on the system’s development had a convergence, with the economic and demographic system being the main constraining subsystems, and the obstacle degree of the environmental system was increasing year by year. [Conclusion] The overall level of coupled and coordinated development of the PEE system in the reservoir area was improving, and regional differences were narrowing. In the future, the focus should be on the optimization of a single system to the coordination of multiple systems, and adjustments should be made from both the perspectives of the system itself and regional synergy, in order to strengthen policy and institutional regulation and scientifically explore the development path.

Abstract:[Objective] The ecological environment of the Kuye River Basin plays a critical role in the larger context of the Yellow River Basin’s health. Understanding the ecosystem services it provides is crucial for sustainable development.[Methods] Using the InVEST model, researchers conducted a quantitative assessment of ecosystem service functions from 1990 to 2020.[Results] (1) There have been some notable changes in land management policy leading to shifts in land use patterns, particularly in construction land expansion and decreased unused land. Additionally, it seems like there’s been a positive impact on vegetation cover, with grassland dominating and overall vegetation coverage showing an upward trend, albeit with fluctuations. (2) The ecological service function of the Kuye River Basin showed a trend of first declining around 2000 and then fluctuating and increasing after 2010, and the habitat quality index was basically stable between 0.22~0.24, and the overall habitat quality was poor. (3) The soil conservation and habitat quality index in the watershed was dominated by the distribution of low-low aggregation cold spots, the spatial distribution of carbon storage and water conservation cold spots and hot spots was relatively scattered, and the high and low values were spatially staggered. The soil conservation and habitat quality index were mainly low-value aggregation, and the spatial distribution of carbon storage and water conservation was fragmented. (4) In the past 30 years, carbon storage and habitat quality were mainly affected by land use, and soil conservation and water conservation were mainly affected by topography, soil type and precipitation.[Conclusion] The findings of this study highlight the intricate interplay between land use, topography, soil type, precipitation, and their impacts on carbon storage, habitat quality, soil conservation, and water conservation in the Kuye River Basin. Understanding these dynamics is crucial for devising effective strategies to enhance ecological services and allocate appropriate soil and water conservation measures.

Abstract:[Objective] This study aims to investigate the carbon storage, carbon sink function, and response mechanism to climate in Pinus sylvestris var. mongolica plantations with different initial planting densities on the southern edge of Horqin Sandy Land. The goal is to facilitate the assessment of the carbon sequestration function and adaptive management of forest ecosystems.[Methods] Estimating carbon storage and carbon sequestration rate of Pinus sylvestris plantations using stand height and cross-sectional area, and analyzing their responses to temperature, precipitation, and evaporation in conjunction with meteorological factors. The GM (1,1) grey prediction model was used to predict forest carbon storage in 2030. [Results] The carbon storage and sequestration rate of Pinus sylvestris plantations with different initial planting densities exhibited similar annual fluctuations, with an overall increase in carbon storage each year. The curve of the sequestration rate showed a "U" shape. Both thinly and excessive initial planting densities can reduce the carbon carbon sequestration capacity of Pinus sylvestris plantations. Before reaching 32 years old, the highest carbon sequestration intensity was observed in stands with initial planting densities of 1 500~2 000 tree/hm², and for stands aged 35~46 years, the optimal density was 1 000~1 200 tree/hm². The carbon storage increased logarithmically with increasing stand density.The response pattern of the planted Pinus sylvestris forests’carbon sequestration rate differed among stands with different initial planting densities regarding temperature but not precipitation. For high and extremely high-density Pinus sylvestris plantations, the average temperature in August of the previous year and in March, May, June and July of the current year were the main climatic factors limiting carbon sink. For low and medium-density plantations, the average temperature in August of the previous year and in March and October of the current year were the main climatic factors that constrain carbon sink. The correlation analysis between evapotranspiration and carbon sequestration rate in different planting density stands showed that carbon sink of low-density Pinus sylvestris plantations was more sensitive to evapotranspiration. Based on the GM (1,1) grey model, it was found that excessively high or low initial planting density would reduce the carbon sequestration potential of future Pinus sylvestris plantations. The optimal planting density for carbon sequestration rate was 1 772 tree/hm². [Conclusion] The initial planting density of Pinus sylvestris has a significant impact on carbon storage and carbon sequestration, as well as their response to climate change in sandy areas. Adjusting the initial planting density may be one of the key adaptive management measures for Pinus sylvestris plantations under climate change.

Abstract:[Objective] This paper aims to deepen the understanding of the carbon cycle by analyzing the spatiotemporal evolution characteristics of carbon storage in the central Yunnan urban agglomeration and its response to land use/land cover (LULC) change, so as to effective guidance for carbon management and ecological restoration strategies. [Methods] InVEST and PLUS models were used to simulate and predict the spatiotemporal evolution patterns of carbon storage in the central Yunnan urban agglomeration from 1990 to 2030. By combining data on LULC change, the relationship between carbon storage and LULC change was quantitatively analyzed. [Results] (1) From 1990 to 2020, the land types of the central Yunnan urban agglomeration were mainly forestland, cropland, and grassland, and forestland, cropland, and construction land showed an increasing trend, among which construction land increased the largest. (2) Carbon storage in the central Yunnan urban agglomeration presented a change characteristics of "first increase and then decrease, gradually stabilize", reaching a maximum value of 1.46×10⁹ t in 2000, and decreasing to 1.45×10⁹ t in 2020, showing a spatial distribution characteristic of "higher in the west, lower in the east". (3) The carbon storage predictions under different future development scenarios indicated that, compared with 2020, all four scenarios showed a declining trend in carbon storage by 2030, among which the ecological development scenario experienced the least decline, with a reduction of 0.43×10⁷ t compared with 2020, while the cropland development scenario exhibited the most significant decline, with a reduction of 1.05×10⁷ t compared with 2020. (4) The conversion between cultivated land and forestland was the primary factor affecting carbon storage. Specifically, the transformation of cultivated land into forests plays a crucial role in increasing carbon storage in the central Yunnan urban agglomeration. Forest expansion significantly enhanced regional carbon storage, while a reduction in grassland negatively impacted carbon storage. [Conclusion] The conversion of forestland and cultivated land has a significant impact on increasing or decreasing carbon storage in the central Yunnan urban agglomeration.

Abstract:[Objective] This paper explores the spatial-temporal pattern and influencing factors of green land use efficiency in Beijing-Tianjin-Hebei, and provides theoretical reference for promoting the green development and transformation of land use and optimizing the spatial development and protection pattern of land. [Methods] Taking Beijing-Tianjin-Hebei as the research area, we constructed a land green utilization efficiency evaluation index system, used the SBM-DEA model and exploratory spatial data analysis (ESDA) to reveal the characteristics of spatial and temporal patterns of land green utilization efficiency in Beijing-Tianjin-Hebei, and explored the influencing factors by using the Tobit multiple regression model. [Results] (1) Since 2008, the overall green land use efficiency in Beijing-Tianjin-Hebei has been on the rise, especially since 2012, which has reached an effective state. (2) The spatial non-equilibrium characteristics of "high in the middle and low in the surroundings" are shown in the space, with Beijing and Tianjin in the high-efficiency centers, and the positive spatial correlation in the whole area is significant and increasing, the local spatial agglomeration characteristics are obvious, and the efficiency value correlation characteristics among the neighboring cities are significant. (3) Economic development and ecological governance have a significant positive impact on the improvement of land green use efficiency, with the level of economic development having the most prominent impact, while land urbanization and population agglomeration reflect a significant negative impact. [Conclusion] It should accelerate the promotion of the green development transition in Beijing-Tianjin-Hebei, further deepen the Beijing-Tianjin-Hebei synergistic development, and focus on improving the level of economic development in inefficient regions. It is recommended that the optimization of the spatial development and protection pattern of land be strengthened, a strict land-use system be implemented, the restoration and maintenance of land ecosystems be strengthened, and initiatives to improve the efficiency of the green use of land be formulated in a differentiated manner, so as to comprehensively promote the improvement of the efficiency of green land use.

Abstract:[Objective] In order to quantitatively evaluate the suitability and quality improvement potential of forest and grass in typical watersheds of complex underlying surface in the middle reaches of the Yellow River. [Methods] The evaluation index system and evaluation method of forest and grass suitability in Sanchuan River Basin were constructed by means of geographical detector, spatial analysis, mathematical statistics and other methods, and the forest and grass suitability and its potential for quality improvement under the current land use conditions in the basin were evaluated. [Results] (1) The dominant factors affecting the suitable distribution of forest land in the Sanchuan River Basin include the fraction of absorbed photosynthetically active radiation (FPAR), elevation, soil erosion intensity and soil type. The dominant factors affecting the suitable distribution of grass land include elevation, FPAR, soil type and soil moisture, etc. (2) The area of forest land with different suitability degrees was from large to small high suitability, unsuitable, mid-height suitability, moderate suitability, and the area above moderate suitable accounted for 81.9% of the total area of forest land. The area of grassland with different suitability degree was in order from large to small: moderate suitability, unsuitable, mid-height suitability, and high suitability, and area above moderate suitability accounts for 55.3% of the total area of grassland, and there was still a large space for optimization layout of grassland in the basin. (3) The area of forest land improvement was 223.2 km², accounting for 15.4% of the total area of moderate suitability and above areas, and most of the forest land in the area had reached the coverage threshold level. The area of grade I upgrading potential of forest in each suitability area accounted for more than 89.0%, and the difficulty of upgrading was low. The area of grassland improvement was 222.3 km², accounting for 43.1% of the total area of moderate suitability and above areas, and nearly half of the grassland in the area have not yet reached the coverage threshold; The area proportion of grade I upgrading potential of grassland in each suitability area decreased with the increase of suitability, and the difficulty of upgrading increased with the increase of suitability. (4) The forest land can implement weak intervention measures based on natural restoration by strengthening the control of closure; grassland needs to take appropriate intervention measures according to the potential zoning of different suitability to achieve the overall improvement of grassland coverage. [Conclusion] In the Sanchuan River Basin, the pattern of forest land was better than that of grassland and the potential of grassland improvement is higher than that of forest land. The evaluation method of forest and grass habitat suitability constructed in this study can provide a scientific basis for the rational allocation of plant measures and the improvement of quality and efficiency in the middle reaches of the Yellow River.

Abstract:[Objective] Gramineae-legume intercropping can give consideration to production and ecological benefits, improve nitrogen use efficiency and reduce nitrogen pollution. At present, the process of nitrogen utilization, absorption and transfer distribution in gramineae-legume intercropping systems under different water conditions is not clear. [Methods] The above ground biomass, nitrogen absorption and utilization, nitrogen fixation rate, and nitrogen transfer rate of gramineae-legume intercropping were studied by using water treatment with the same total water amount in 2 periods but with an interval of 3 or 5 days, combined with root separation (non-separation, nylon mesh separation and plastic plate separation) and nitrogen isotope labeling methods. [Results] The aboveground biomass, nitrogen content and nitrogen accumulation of E. dahuricus intercropped with alfalfa were significantly increased compared with monoculture E. dahuricus, while, for alfalfa, the intercropping with E. dahuricus resulted in a decrease compared to monoculture alfalfa. Under the condition of the same total water amount, the above-ground biomass of the herbage increased by 6.28% and 17.32%, respectively, by high-frequency water treatment compared with medium and low frequency water treatments, and the nitrogen fixation rate of alfalfa was increased by 39.82% and 44.81%, respectively, under high-frequency water treatment compared with medium and low frequency water treatments. However, the nitrogen concentration and nitrogen accumulation under some middle and low frequency water treatments were significantly higher than those under high frequency water treatment (p < 0.05), and promoted nitrogen transfer. Root separation weakened the interaction between grass and bean, and showed that as root separation increased the aboveground biomass, nitrogen concent and aboveground nitrogen accumulation of intercropping alfalfa, and decreased the corresponding indexes of intercropping E. dahuricus. The nitrogen fixation and nitrogen transfer rate of alfalfa intercropping were in the order of no separation > nylon mesh separation > plastic plate separation. [Conclusion] Moderate water regulation can improve the advantages of gramineae-legume intercropping, and root interaction is the key to promote the biological nitrogen fixation and nitrogen transfer of legume herbage.

Abstract:[Objective] To investigate the effects of different straw returning methods on the temperature of black soil during seasonal freeze-thaw period. [Methods] By monitoring the field temperature, the soybean field was selected as the research object, and two types of returning methods were set, namely, straw mulching (FG) and straw mixing(FH). The amount of returned straw was 30% (59 670 kg/hm²), 60% (119 340 kg/hm²) and 90% (179 010 kg/hm²), respectively, and the bare land was designated as the control treatment (CK) in a total of seven treatments. Four soil depths of 5, 10, 20 and 30 cm below the surface along the vertical profile of soil were set to analyze the characteristics of soil temperature changes during the freezing and thawing period under different straw return methods and amounts. [Results] (1) Straw returning to the field resulted in the soil entering various freeze-thaw stages at a time lagging behind that of the bare land, and effectively raised the range of the minimum soil temperature and lowered the maximum temperature, of which both the maximum temperature raising and lowering occurred in the FG90 treatment, which were 3.0~6.1 ℃ and 1.5~5.2 ℃, respectively. (2) Straw returning weakened the soil temperature variability and correlation with air temperature. The maximum coefficient of variation and coefficient of variation and correlation occurred in the bare soil layer of 5 cm, which were 6.54 and 0.82, respectively. The minimum occurred in the 30 cm soil layer of the FG90 treatment, with values of 0.82 and 0.26, respectively. The relationship between soil temperature variability was CK>FG30>FH30>FH60>FG60> FH90>FG90, and the relationship between soil temperature and air temperature was CK>FH30>FG30>FH60>FH90>FG60>FG90 >FG90. (3) The freezing and thawing rates of bare land were the highest and the freezing-thawing periods were the shortest, with a freezing rate of 0.19 ℃/h and thawing rate of 0.60 ℃/h. The minimum freezing rate occurred in FH90 treatment (0.04 ℃/h) and the minimum thawing rate occurred in FG90 treatment (0.05 ℃/h). (4) With the increase of soil depth, the soil freezing stage and thawing stage gradually increased, but the freezing duration gradually decreased. The effect of delaying freeze-thawing was most obvious in the FG90 treatment, with the freezing stage and thawing stage of 8 and 10 days, respectively. [Conclusion] The results of the research quantitatively described the temperature characteristics of black soil under different straw return measures during freezing and thawing periods, and clarified the differences in soil temperature effects between different straw return measures, which is of great significance in guiding the rational use of straw resources and conservation tillage in black soil areas.

Abstract:[Objective] To investigate the spatial variability of trail soils under the influence of anthropogenic trampling in the understory social activities in karst areas. [Methods] To investigate the spatial and temporal variability of soil properties in the 0—20 cm soil layer under drought and precipitation conditions, we took the karst forest trail area as the research object, regularly sampled the soil at a fixed piont on a monthly scale. Geostatistical analyses were performed to assess the spatial and temporal variability of soil properties and their distribution patterns under both drought and precipitation conditions. [Results] Anthropogenic trampling can alter the structure of the soil surface (0—15 cm) and subsurface by increasing soil consolidation and the aggregation capacity of soil particles. The spatial distribution of soil water content in karst forests trails showed moderate variability, with higher values observed in the center of the trails (32.68%) compared to the trail edges (28.46%) and the forest interior (26.99%). Soil compactness and shear strength followed a similar pattern, being highest at the center of the trail, followed by the trail edge, and lowest in the forest interior. Vegetation cover was weakened by anthropogenic trampling, resulting in an increased response time of soil water content to rainfall events. Stochastic factors had a relatively greater influence on soil surface water content but overall showed strong spatial autocorrelation (<25%). Under changing meteorological conditions, both nugget and sill values for soil moisture in the surface layer of forest trails were negatively correlated with mean soil moisture content. The spatial distribution of soil moisture was modeled using range R under drought and precipitation conditions as 30.89 and 39.49 m respectively, with Gaussian model showing optimal fit (R²＞0.97). Kriging contour plots revealed patchy distribution patterns for soil moisture along forest trails, which exhibited better spatial continuity under precipitation conditions. [Conclusion] Substantial guidance for the implementation of woodland ecological restoration strategies and the development of more accurate soil sampling density programmers in karst areas.

Abstract:[Objective] Gravel is an important factor affecting soil porosity and water infiltration. Therefore, it is of great significance to determine the specific soil porosity characteristics that are impacted by gravel-induced changes. [Methods] Taking lime soil with high gravel content in southwest karst area as the research object, CT scanning and one-dimensional soil column infiltration test were used to compare and analyze the soil pore characteristics and water infiltration characteristics under two gravel particle sizes (2.0~5.0 and 5.0~12.5 mm) and five gravel contents (0, 10%, 20%, 30%, 40%). The structural equation model was used to explore the coupling relationship between soil pore characteristics and infiltration characteristics. [Results] (1) The macroporosity, pore connectivity, pore shape factor, pore surface area and pore volume of gravel-bearing soil are higher than those of gravel-free soil. When the gravel content was 20% and 30%, there was significant difference between pore connectivity and pore shape factor (p < 0.05). (2) Gravel improved soil infiltration performance, with stable infiltration rates of gravel content from 10% to 40% being 4.02, 5.00, 2.88 and 5.14 times higher than those of gravel-free soils, and cumulative infiltration being 1.67, 1.76, 2.49 and 2.39 times higher, respectively, for particle sizes ranging from 2.0 to 5.0 mm. When the particle size was 5.0~12.5 mm, the stable infiltration rate was 2.20, 2.67, 4.78 and 2.78 times of that without gravel, and the cumulative infiltration amount was 1.42, 1.75, 2.46 and 2.02 times of that without gravel, respectively. (3) In the structural equation model, gravel content was positively correlated with pore connectivity and pore equivalent diameter. Pore connectivity had the greatest influence on the steady infiltration rate, and pore equivalent diameter had the greatest influence on the cumulative infiltration rate. [Conclusion] Gravel content promotes water infiltration mainly by increasing soil pore connectivity and pore equivalent diameter. The research results can provide scientific basis and theoretical reference for further understanding the hydrological process of gravel-bearing soil in southwest karst area.

Abstract:[Objective] Biochar application can change soil physicochemical properties. The study of the effects of different biochar application methods on soil moisture, temperature and electrical conductivity (EC) distribution, which can provide basis for the scientific management of seasonally frozen soil. [Methods] The effects of different biochar application methods on soil liquid water content, temperature and EC during freezing period were studied by field experiment and long-term observation in black soil region of northeast. Biochar application methods included one-time biochar mixed application of 40 t/hm²(HO), biochar bottom application of 40 t/hm² (HE), and the blank was 0 t/hm² (CK). [Results] Both biochar application methods increased the mean soil liquid water content during the freezing period (p < 0.05), as HO > HE > CK. The application of biochar application significantly increased soil EC throughout the experimental cycle, and the average soil EC increased by 17.73% and 6.89% in the HO and HE treatments, respectively, compared to CK. The two biochar application methods had different effects on the soil temperature. Compared with CK, the mean soil temperature increased by 0.32 ℃ in the HE treatment, while the mean soil temperature decreased by 0.46 ℃ in the HO treatment. In addition, the HE treatment weakened the range of change in soil liquid water, temperature and EC during the freezing period compared to HO and CK treatments. [Conclusion] Both heterogeneous and homogeneous biochar application were beneficial to increase the liquid water content and EC of degraded black soil during freezing period. Especially heterogeneous biochar application was also beneficial to increase the soil temperature of the tillage layer during freezing period, homogeneous biochar application can also reduce the soil freezing during freezing effect during the same period. Both of the two biochar application modes may have an important impact on the soil moisture-salt transport and material transformation process during the freezing period, and even have an important effect on the spring emergence and early growth of crops.

Abstract:[Objective] The objective of this study was to analyze the spatial distribution characteristics of surface soil moisture content in the rocky desertification slope under different land preparation measures and to provide references for improving water resources utilization efficiency and agricultural management level on rocky desertification slopes. [Methods] The citrus forest under three land preparation measures of reverse slope, flat terrace,and natural slope on rocky desertification slope were chosen as the research objects. Classical statistics, geostatistics and multifractal theory were used to analyze the spatial distribution characteristics of soil moisture content. [Results] (1) The soil moisture content of the reverse slope was significantly higher than that of the flat terrace and the natural slope (p<0.05). The spatial continuity, aggregation, total and structural variability of soil moisture content on the flat terrace were stronger than those on the reverse slope and the natural slope. (2) The soil moisture content of different land preparation measures showed moderate variability (10.00%≤CV≤100.00%), strong spatial autocorrelation [C₀/(C₀+C)≤0.25], and extremely significant (p<0.01) spatial aggregation. (3) The distribution of soil moisture content under different land preparation measures has multi-fractal characteristics. During the dry season, the distribution range of soil moisture content was narrowest on the reverse slope, and more discrete on the natural slope. During the rainy season, the distribution range of soil moisture content was narrowest on the flat terrace, and more uneven on the reverse slope. [Conclusion] Soil mechanical composition was the main factor that affected soil moisture content, and the reverse slope was more conducive to improved soil moisture conditions on rocky desertification slopes.

Abstract:[Objective] In order to grasp the current situation and spatial variability pattern of black soil layer thickness in the typical black soil region within a small watershed, and realize dynamic monitoring of black soil layer thickness in such areas. [Methods] This study selected a small watershed of Heshan Farm in Nenjiang City, Heilongjiang Province. Soil sampling points were uniformly distributed at intervals of 100 meters, and undisturbed soil samples were collected from surface to parent material using soil augers to determine the thickness of the black soil layer. Meanwhile, terrain and land use data were extracted based on UAV aerial photography data. The study analyzed the thickness of black soil layer in the small watershed and its influencing factors. [Results] Among the 295 sampling points in the small watershed, the thickness of black soil layer varied from 0 to 160 cm, with an average of 44.1 cm. "Popihuang" (black soil layer thickness ≤20 cm) accounted for 17.63%, thin black soil (<30 cm) comprised 43.39%, medium layer (30—60 cm) constituted 36.27%, and thick layer (>60 cm) accounted for 20.34%. Thick layer black soil was primarily distributed in the lower slopes, in the vicinity of gullies, and other gently sloping areas of the watershed, while thin layer black soil was predominantly found in steep slopes and areas with sandy gravel parent material, and medium layer black soil was predominant in other regions. Terrain indices such as topographic position index, curvature, slope exhibited significant correlations with the black soil layer thickness. The thickness of black soil layers in cultivated land was significantly lower compared to grassland and forest land. [Conclusion] The thickness of black soil layer exhibits significant spatial heterogeneity within the small watershed, which is primarily influenced by terrain characteristic, parent material and landuse. The research findings can be used as one of the bases for dynamic monitoring of regional black soil layer thickness, and can provide data support for the formulation of soil and water conservation measures in small watershed.

Abstract:[Objective] To investigate the effects of long-term application of controlled-release urea on soil acidity, acid-base buffering capacity and fertility of northern calcareous tidal soils. [Methods] Based on a long-term field trial of positioning fertilization since 2008, two types of nitrogen fertilizers, blended controlled-release urea(CRF) and ordinary urea(BBF), and three levels of nitrogen application, namely, no nitrogen application (N 0 kg/hm²), constant nitrogen application (N 540 kg/hm²) and incremental nitrogen application (N 810 kg/hm²), were designed, and soil samples were collected from 0-80 cm during the ripening of the maize season of 2022 to determine the acid-base buffering capacity, soil calcium carbonate content and soil fertility of soil. Samples were collected from 0-80 cm soil at the maturity of the corn season in 2022 to determine the soil acid-base buffer capacity, soil calcium carbonate content and soil nutrients. [Results] (1) CRF slowed down the decline of soil buffer capacity and pH value caused by N application and alleviated the process of soil acidification. The buffer capacity of constant CRF and incremental CRF treatments increased by 5.22% and 11.17%, respectively, and the pH of constant CRF and incremental CRF treatments increased by 0.17 and 0.08 units, respectively, compared with that of constant BBF and incremental BBF. (2) CRF increased the soil cation exchange and exchangeable calcium and magnesium content and increased the active calcium carbonate content of the tillage soil, and the active calcium carbonate content of the constant CRF and incremental CRF treatments increased by 52.08% and 45.31% compared with that of the constant BBF and incremental BBF treatments. Meanwhile, CRF slowed down the loss of soil calcium carbonate content in deep soil layers. (3) CRF increased soil total nitrogen, organic matter, nitrate nitrogen and ammonium nitrogen content. [Conclusion] Long-term application of CRF alleviated soil acidification caused by nitrogen fertilizer application, increased soil active calcium carbonate content, and improved soil fertility.

Abstract:[Objective] To investigate the water purification capabilities of Polygonum species and assess their suitability for the remediation of domestic sewage. [Methods] Polygonum hydropiper, Polygonum orientale, Polygonum divaricatum and Polygonum lapathifolium were selected as the research objects. The removal effects of total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and total phosphorus (TP) in two concentrations of domestic sewage by these four species of Polygonum were discussed through a simulated hydroponic experiment. Additionally, the accumulation ability of Polygonum species to nitrogen and phosphorus in sewage was examined. [Results] (1) All four species of Polygonum exhibited good removal effects on nitrogen and phosphorus in two concentrations of domestic sewage. (2) Under high concentration sewage treatment, the removal rates of TN, NH₄⁺-N and TP by Polygonum orientale, Polygonum divaricatum and Polygonum lapathifolium were 96.04%~97.41%, 94.60%~97.79% and 98.78%~99.68% (28 days), respectively, which were significantly higher than those of Polygonum hydropiper (p<0.05). (3) Under low concentration sewage treatment conditions, the shoot nitrogen and phosphorus accumulation of four species of Polygonum were 27.38~37.47 mg/plant and 7.65~10.11 mg/plant, respectively, with no significant difference between plants; Under high concentration sewage treatment, Polygonum orientale exhibits a strong nitrogen accumulation capability, with shoot nitrogen accumulation reaching 57.16 mg/plant, while Polygonum lapathifolium exhibits a strong phosphorus accumulation capability, with shoot phosphorus accumulation reaching 15.32 mg/plant. Conversely, Polygonum hydropiper displays weak nitrogen and phosphorus accumulation abilities. [Conclusion] These findings indicate that all four Polygonum species can be used to the remediation of low-concentration domestic sewage. Among them, Polygonum orientale, Polygonum divaricatum, and Polygonum lapathifolium are more suitable for treating high-concentration sewage. This study offers valuable insights into selecting plant materials for remediating domestic sewage.

Abstract:[Objective] Current research mainly focuses on long-term frequency studies in non-karst areas, but there is insufficient research on hydrochemical sampling frequency under different rainfall levels in karst areas Inorder on determining the optimal sampling frequency of hydrochemistry at different rainfall levels in Karst small watersheds. [Methods] Based on high-frequency electrical conductivity (EC) data of different rainfall levels (heavy rainstorm, heavy rain and moderate rain) with a 1 hour interval from June 2022 to July 2023 in the typical Karst small watershed of the central Guizhou Plateau, low-frequency data of 2~15 hours were resampled. Combined with various evaluation indicators and catastrophe point theory, the optimal sampling frequency of hydrochemistry under different rainfall levels in the Karst small watershed was determined. [Results] (1) Due to the influence of geological background, the hydrochemistry response to rainfall in the small watershed of the Karst area is characterized by rapid rise and fall, and the loss of sampling error is large. (2) Factors such as I₆₀ (maximum 60 min rainfall intensity), the number of rain-free days, and the amount of rainfall all impacted the hydrological process, which in turn altered the characteristics of hydrochemical changes and ultimately affected the sampling frequency; (3) It was recommended to use a sampling frequency of 4 hours during heavy rain events, a frequency of 5 hours during moderate rain events when I₆₀>10 mm/h, and 6 hours frequency when I₆₀ was small (I₆₀<10 mm/h). [Conclusion] The research results provide reference for hydrochemical monitoring in karst small watershed.

Abstract:[Objective] To investigate the effect of binding agent on the aggregation of soil colloidal particles and to clarify the microscopic mechanism of the formation of soil aggregate structures. [Methods] Soil nanoparticles (NP) were obtained from Lou soil, namely NPs from original Lou soil (NP-Lou), NPs from organic carbon-removed soil (NP-OCR), and NPs from inorganic carbon-removed soil (NP-ICR). The aggregation kinetics, critical coagulation concentrations (CCCs) and surface electricity of three kinds of Lou soil nanoparticles in Na⁺, Ca²⁺ and La³⁺ systems were determined by dynamic light scattering. The Hamaker constant and interaction energy of soil nanoparticles were calculated by Derjauin-Landau-Verwey-Overbeek (DLVO) theory. [Results] In the same solution chemistry condition, the aggregation rate of NP-OCR and NP-ICR decreased and the CCCs value increased compared with NP-Lou. The absolute value of zeta potential of NP-OCR and NP-ICR was lower than that of NP-Lou, which resulted in the decrease of electrostatic repulsive potential energy between nanoparticles. The theoretical calculation of DLVO showed that the Hamaker constant of NP-OCR and NP-ICR was also lower than that of NP-Lou. That was, the attractire van der Waals potential energies of soil nanoparticles also decreased after the removal of inorganic carbon and organic carbon. The combined force calculation results showed that the total potential energy of the interaction between soil nanoparticles after removing inorganic carbon or organic carbon was higher than NP-Lou, so the CCC value was larger. The CCCs difference between NP-ICR and NP-Lou was larger than the CCC difference between NP-OCR and NP-Lou, therefore, soil inorganic carbon affected Lou soil NP aggregation more strongly. [Conclusion] Inorganic carbon and organic carbon enhance the attractive potential energy by increasing the Hamaker constant of the interaction between soil particles, which is important for cementing materials to promote the stability of soil aggregates.