Abstract:[Objective] The types of soil and water conservation measures and their configuration modes are complicated. Accurate identification and fine extraction of detailed configuration information of soil and water conservation measures are the basis for obtaining the factor values of soil and water conservation measures. [Methods] The information acquisition methods of soil and water conservation measures mainly include traditional field surveys, satellite remote sensing images, and UAV close-range photography. The identification and extraction methods mainly include visual interpretation, traditional machine learning, object-oriented classification methods, and deep learning models. By combing the research results of identification and extraction methods of soil and water conservation measures at home and abroad, the existing shortcomings are summarized and the research prospects are put forward. [Results] In semantic segmentation, future feature fusion and multimodal learning, weak supervision and semi-supervised learning, integrated learning and meta-learning can be applied to the extraction of soil and water conservation measures. [Conclusion] At present, there are few reports on the results of identification and extraction of soil and water conservation tillage measures. However, tillage measures are common in agricultural practice, and the research on identification and extraction of tillage measures should be strengthened in the future. Artificial intelligence combined with big data technology is the development direction of efficient and accurate identification and extraction of soil and water conservation measures in the future. It is necessary to further study the use of semi-supervised and weakly supervised learning methods, combined with multi-modal learning, small sample labels and other methods to obtain high-quality labeled sample data for soil and water conservation. Extraction of point and linear engineering measures; the combination of deep learning algorithms such as multimodal learning and instance segmentation methods with object-oriented classification methods is applied to the identification and extraction of soil and water conservation plant measures to improve the classification and extraction accuracy of different soil and water conservation plant measures. So as to improve the information extraction method of various soil and water conservation measures, and provide support for accurately obtaining the factor value of soil and water conservation measures and calculating the carbon sink capacity of soil and water conservation.

Abstract:[Objective] Kuye River Basin is the main source of erosion in the coarse sand area in the middle reaches of the Yellow River. The study is aimed at elucidating the spatio-temporal pattern of soil erosion, predicting the development trend of soil erosion in Kuye River Basin and providing decision support for the comprehensive control of soil erosion in the future. [Methods] Based on the multi-source data from 2010 to 2020, the spatial distribution of soil erosion in the Kuye River Basin was studied, and the characteristics of soil erosion intensity change were analyzed by using quantitative indicators such as dynamic degree of soil erosion intensity, information entropy of soil erosion intensity, comprehensive index of soil erosion intensity and transfer matrix. The CA-Markov model was established to predict the soil erosion in 2025. [Results] (1) The soil erosion intensity in the study area was mainly in micro and mild erosion, accounting for more than 70% of the total area, and stronger erosion was mainly distributed in the middle and lower reaches of the basin and tributary Beiniuchuan. From 2010 to 2020, the average soil erosion decreased from 1 955.56 t/(km²·a) to 892.98 t/(km²·a), the area of micro erosion increased significantly, and the area of other erosion intensity decreased correspondingly. The soil erosion intensity remained unchanged or decreased in most regions, and only less than 3% of the regions experienced increased erosion intensity. (2) The dynamic degree of intensity, extreme intensity and extreme erosion in Kuye River Basin changed greatly, the information entropy of soil erosion intensity decreased steadily from 1.29 to 0.81, the comprehensive index of soil erosion intensity decreased from 178.96 to 76.61 and the decline rate was higher in the first five years, and the change of soil erosion intensity in the basin to the weakening direction mainly occurred between the two adjacent erosion intensity levels. (3) CA-Markov model simulation shows that, it is expected that by 2025, the soil erosion situation in the basin will be further improved, with the proportion of micro erosion accounted more than 75%. [Conclusion] From 2010 to 2020, the soil erosion situation in the study area continued to improve, and the control efficiency of soil erosion in the next five years was higher, and the soil erosion situation in the basin would be further improved in 2025.

Abstract:[Objective] Revealing the effects of different management measures on runoff and sediment yield and soil characteristics of [Panax notoginseng(Burkill) F. H. Chen] forest land, can provide a theoretical basis for scientific prevention and control of soil erosion in understory P. notoginseng cultivation. [Methods] The in-situ observation experiment of field runoff plot was used to quantify the sediment yield of natural forest land (CK), forest prepared land (SP), no canopy P. notoginsengforest land (NC), and canopy P. notoginseng forest land (HC) at different slopes (5°,10°,15°) in the rainy season of 2022. to explore the effects of different management measures on the runoff and sediment yield and soil characteristics of P. notoginseng forest land slope. [Results] (1) The total rainfall in Xundian County in 2022 was 1031.70 mm, which belonged to a flat year. The cumulative erosive rainfall outside and inside the forest was 845.40 and 565.60 mm, Canopy interception rates ranged from 9.97% to 67.38%. (2) There were extremely significant (p<0.01) differences in runoff and sediment yield of P. notoginseng forest land under different management measures. Compared with CK, the average total runoff of SP, NC, and HC increased by 272.23%, 171.19%, and 106.89%, respectively, and the average total sediment yield increased by 385.15%, 248.82%, and 138.84%, respectively. With the increase of slope, the loss increased more significantly. The canopy in P. notoginseng forest has a good effect on sediment reduction. (3) Soil characteristics of CK and SP were significantly different from those of other management measures; There were significant differences in the mean geometric diameter and soil anti-scour coefficient between NC and HC (p<0.05), but no significant differences in other soil characteristics. Principal component analysis showed that soil saturated water conductivity, litter storage, soil bulk density and K value of cultivation P. notoginseng forest had great effects on sediment yield. (4) There was a significant power function relationship between event runoff and sediment yield in the P. notoginseng forest land and rainfall or rainfall erosivity and rainfall intensity (p<0.05); total runoff and sediment yield showed a significant positive exponential relationship with slope (p<0.01), R²>0.90. With the increase of slope, the loss of sediment increased more. [Conclusion] Forest land preparation and P. notoginseng cultivation led to a significant increase in soil erosion, but the maximum soil loss [34.53 t/(km²·a)] was far lower than the allowable soil loss in karst area of southwest China. It is recommended to cultivation P. notoginseng in gentle slope forest land, and hydraulic erosion can be alleviated by building canopy and improving soil characteristics.

Abstract:[Objective] To investigate the impact of intermittent rainfall on the amount and sorting characteristics of black soil splash erosion. [Methods] This study is based on artificial simulated rainfall experiments, with two rainfall intensities (40, 70 mm/h) designed, each with 5 rainfall events, to analyze the splashing erosion amount and particle size distribution characteristics of black soil under different rainfall conditions. [Results] Under two different rainfall intensities, there is a dynamic development process of alternating strength between "no crust weak crust strong crust weak crust new crust" in the soil surface layer of different rainfall sites. Under two different rainfall intensities, the maximum values of splashed aggregate MWD and GMD appeared in the fourth rainfall, and the minimum values appeared in the first rainfall. The agglomerates with a particle size of 5~2 mm did not migrate in each rainfall, and the splashed agglomerates were mainly composed of particles with a size of 2~0.25 mm, accounting for 36.49%~58.61% and 49.10%~60.09% of the splashed erosion amounts of the two rainfall intensities, respectively. The erosion amount of the five rainfall events showed a trend of first increasing and then decreasing with the decrease of particle size, while the mass percentage with particle size <0.053 mm showed a trend of first decreasing and then increasing with the increase of intermittent frequency. The mass percentage with particle size <0.053 mm all showed the minimum value in the third rainfall event, which was 18.21% and 17.63%, respectively. [Conclusion]Rainfall can lead to the formation of soil crust, and the thickness of soil crust shows dynamic changes with the increase of rainfall frequency. In the third rainfall, the soil crust thickness is the highest, and at this time, the splash erosion amount has the minimum value, mainly greater than 0.053 mm. The research results provide reference for the study of soil water erosion mechanism in the black soil area of Northeast China.

Abstract:[Objective] Soil resistance reflects the characteristics of soil to mitigate erosion and is quantified by rill erodibility (K_r) and critical shear stress (τ_c). To investigate the difference of soil resistance and its main controlling factors under different land use types through the flume scouring test, which provided a theoretical basis for revealing the dynamic mechanism of soil erosion in Northeast black soil area. [Methods] Seven typical land use types were selected in the Hebei small watershed of Heshan farm, located in Nenjiang city of Heilongjiang Province. K_r and τ_c were determined using the measured soil detachment capacity by scouring test in a large hydraulic flume. The dominant factors influencing soil resistance were determined by correlation analysis and partial least square regression. [Results] (1) The estimated K_r varied from 0.003 to 0.372 s/m among different land use types. K_rof road was the highest. Compared to cropland, K_r of grassland, transverse forest belt, woodland, longitudinal forest belt, and shrub land decreased by 94.00%, 86.20%, 84.00%, 83.60%, and 71.60%. The fitted τ_c ranged from 4.84 and 13.85 Pa. Cropland and road had lowest τ_c (4.84 and 9.80 Pa). The differences in τ_c were not significant between other land use types and were greater than 10.00 Pa. (2) Correlation analysis showed that K_r was significantly correlated with clay content, aggregate stability and organic matter content (p<0.01), and sand content, soil cohesion, root mass density and litter density mixed within topsoil layer negatively (p<0.05). It was significantly correlated with silt content positively (p<0.01). τ_c was significantly related to silt content negatively (p<0.01). It was significantly correlation with sand content and topsoil litter density (p<0.01), and organic matter content and root mass density positively (p<0.05). (3) The results of PLSR analysis demonstrated that the dominant factors influencing K_r were soil clay content, silt content, aggregate stability, root mass density, organic matter content and litter density mixed within topsoil layer. The key factors affecting τ_c were soil organic matter content, litter density mixed within topsoil layer, silt content and root mass density. [Conclusion] Land use type significantly affects soil resistance. Grassland is most effective at mitigating erosion and is critical for reducing erosion on cropland. Root mass density, litter density, soil texture, aggregate stability and organic matter content are key factors influencing soil resistance. The results of the study provide a theoretical basis for understanding the mechanism of land use type impacting soil erosion dynamics and land use optimization in the black soil area.

Abstract:[Objective]Severe gully erosion in the black soil region of Northeast China is continuously eroding arable land resources, posing a threat to the country's food security. The development of unmanned aerial vehicle (UAV) technology provides an effective way for monitoring gully erosion, but the higher the resolution of data obtained, the longer it takes. The challenge lies in configuring UAV parameters to simultaneously meet accuracy requirements and enhance aerial photography efficiency. [Methods]The Hebei catchment in the rolling hills region of Northeast China was chosen as the study area. Using actual cross-section measurement data as a validation value, the accuracy of gully parameters extracted from UAV data at different resolutions, flight directions, and types was assessed to explore the suitable conditions for various UAV parameter configurations. [Results] (1) Compared with field measurement data, data at a 1 cm resolution extracted the gully parameters with the highest accuracy, the average percentage error for all parameters was less than 5.0%, suitable for monitoring typical gully development processes. Data extracted at 3 cm and 5 cm resolutions had an average percentage error of less than 10.0% for gully width, and the average error increased as gully depth decreased. For gullies deeper than 1 m, the average percentage error was less than 10.0%, suitable for rapid regional sampling surveys. Data extracted at resolutions of 8 cm and 10 cm had average percentage errors greater than 40.0% for gully depth and cross-sectional area, suitable for extracting gully distribution locations and planar parameters. (2) Although fixed-wing UAV obtaining data slightly outperformed in extracting two-dimensional gully features, multirotor UAV using oblique photogrammetry were better in extracting three-dimensional gully features. (3) The average percentage errors for gully depth and cross-sectional area extracted from single-direction oblique photogrammetry data were 1.7 and 1.9 times those from cross-direction data. UAV data obtained from cross-direction flights provided higher accuracy in gully parameter extraction and richer details. [Conclusion] Setting UAV parameters to a resolution of less than 5 cm and obtaining cross-direction oblique aerial photography data can meet the accuracy requirements for monitoring gully morphology in the black soil region of Northeast China.

Abstract:[Objective] To investigate the response mechanism of temporal and spatial distribution of soil organic carbon (SOC) loss to soil erosion intensity, in order to provide basic data for the study of soil carbon cycling mechanism under erosion environment, and provide scientific basis for solving the problem of "thinning and thinning" of black soil. [Methods] This study selected 14 cities (districts or counties) such as Bei'an, Keshan, Kedong and Baiquan counties in the typical black soil area of Songnen Plain as the research objects, and employed the RUSLE model in conjunction with the spatial analysis techniques of GIS to explore the characteristics of temporal and spatial variations in soil erosion and SOC loss in the typical black soil region of Northeast China from 2000 to 2019. [Results] Soil erosion intensity in the study area exhibits a high-north and low-south distribution pattern, predominantly characterized by slight erosion. From 2000 to 2019, the proportion of slight erosion area in typical black soil area showed a inapparent upward trend, while the proportion of slight erosion area and above showed a decreasing trend. Notably, 87.91% of the area did not undergo significant changes in the degree of erosion intensity, with only 3.74% of the are experiencing an escalation in erosion severity. SOC loss exhibited significant spatial distribution differences, generally following a high-north and low-south distribution pattern, with an average annual loss intensity of SOC at 4.74 t/(km²·a). From 2010 to 2019, the total SOC loss showed an increasing trend, with the highest loss occurring in Bei'an, accounting for 37.00% of the total loss in the study area. Between 2015 and 2019, the proportion of areas with soil organic carbon loss intensity less than 5 t/(km²·a) has decreased, while the proportion of areas with loss intensity greater than 5 t/(km²·a) has increased, leading to an increase in the annual average loss intensity. In the northern part of the study area, where soil erosion intensity is high, the abundant SOC content resulted in relatively larger total organic carbon loss upon erosion, giving rise to a distinct regional variation in SOC loss totals. [Conclusion] The temporal and spatial characteristics of SOC loss under the action of erosion, indicating that severe soil erosion is an important driving factor of SOC loss on slope.

Abstract:[Objective] Quantitatively evaluating the magnitude of soil erosion and degradation in the black soil region of Northeast China, can deliver benefits to accurately implement conservation practices in different areas. [Methods] The farmlands in the typical water erosion area of the black soil region of Northeast China were taken as the research objects, and the caesium-137 (¹³⁷Cs) tracing method was applied to quantify soil erosion rate (SER) for different sampling sites. Based on the three categories of black soil degradation, i.e., thinner, poorer, and harder, seven representative indicators were selected, including SER, pH, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), and bulk density (BD). A soil degradation index (SDI) was developed by using total dataset (TDS) and fuzzy membership function methods. [Results] (1) The average SER for different sites displayed an order of Bin County[BX, 8 417.86 t/(km²·a)]>Hailun[HL, 7 083.96 t/(km²·a)]>Gongzhuling[GZL, 3 168.71 t/(km²·a)]>Beian[BA, 2 786.09 t/(km²·a)]> Longjiang[LJ, 2 722.46 t/(km²·a)]. According to the SER, BX and HL were classified as the intense erosion degree, whereas GZL, BA and LJ were classified as the moderate erosion degree; (2) There were significant and negative power function relationships between SER and SOM, TN, TP, but a significant and positive logarithmic relationship between SER and BD (p < 0.05), with R² ranging from 0.222 to 0.532, which indicated that soil erosion substantially exacerbates nutrient loss and soil hardening in black soils; (3) The processes of thinner, poorer, and harder showed significant interactions in the farmlands of black soils. The SDI for different sites followed an order of BX (0.44) > HL (0.36) > LJ (0.21) > GZL (0.10) > BA (0.05). [Conclusion] The findings can provide scientific support for the diagnosis, evaluation and accurate mitigation of soil erosion and degradation in the black soil region of Northeast China.

Abstract:[Objective] This study examines the impact of climate change and human activities on baseflow variability across four representative watersheds within the Loess Plateau: the Wuding River, Kuye River, Yan River, and Tutai River. [Methods] Utilizing daily flow data from 1965 to 2017 for the Wuding, Kuye, and Yan rivers, and from 1983 to 2017 for the Tutai River, alongside multi-site meteorological data, we evaluated the applicability of nine baseflow separation methods and characterized baseflow variations. Contributions of climate change and human activities to baseflow changes were quantified using the elasticity coefficient method within the Budyko framework. [Results] The F4 digital filtering method exhibited superior performance in terms of stability, dispersion, and error metrics, making it the most suitable method for the typical watersheds of the Loess Plateau. Trends in annual baseflow depth, annual runoff depth, and annual baseflow index were consistent across the four watersheds, with multi-year average baseflow indices (BFI) of 0.64, 0.42, 0.28, and 0.49, respectively. Significant decreasing trends (p<0.01) were observed in both annual baseflow depth and runoff depth, while the annual baseflow index showed increasing trends. The contributions of precipitation, potential evapotranspiration, and human activities to the changes in baseflow ranged from -56.72% to 33.92%, -0.81% to 55.16%, and 10.92% to 104.37%, respectively. [Conclusion] The findings underscore that human activities are the principal drivers influencing baseflow evolution in the Loess Plateau area, offering theoretical support for integrated water resource management in the region.

Abstract:[Objective] This study aims to elucidate the impact of freeze-thaw cycles and hydraulic action on soil erosion in the northern rocky mountain regions under varying conditions.[Methods] Utilizing soil samples from the Jiufeng area in Beijing, we conducted simulation tests using indoor runoff scouring and freeze-thaw equipment. We examined the effects of five key factors—freeze-thaw cycle frequency,slope gradient, flow rate, initial soil moisture content, and freeze-thaw temperature differential—on soil sediment yield and anti-scourability.[Results] (1)The sensitivity of the soil’s anti-scourability coefficient to these factors ranks as follows:slope>flow rate>freeze-thaw temperature difference>freeze-thaw cycles>initial moisture content. Notably, slope and flow rate significantly influence the coefficient (p<0.05). For soil sediment yield, the sensitivity ranking is:flow rate>slope>freeze-thaw temperature difference>soil moisture content>freeze-thaw cycles, with flow rate exhibiting a very significant impact (p<0.01), and both slope and freeze-thaw temperature difference showing significant effects (p<0.05). (2) The number of freeze-thaw cycles, slope, and flow rate negatively correlate with the soil's anti-scour coefficient, whereas the temperature difference during freeze-thaw cycles positively correlates with it. The anti-scour coefficient initially decreases and then increases with rising initial soil moisture content. (3) Soil sediment yield increases with higher discharge rates,steeper slopes, and more frequent freeze-thaw cycles,but decreases with an increase in the overall temperature of the freeze-thaw differential. As soil moisture content rises, sediment yield initially increases and then decreases. When the number of freeze-thaw cycles reaches 7 or 10, sediment yield peaks (96.7~99.7 g/min) during the middle phase of runoff scouring (3~6 min) and then stabilizes.[Conclusion] Soil in the northern rocky mountain areas is significantly impacted by various factors under the combined effects of freeze-thaw and hydraulic pressures. The findings of this study provide valuable theoretical support for the prevention and management of combined erosion and for the strategic allocation of soil and water conservation measures in these regions.

Abstract:[Objective] A study on the spatial and temporal patterns of water erosion dynamic factors and their responses to atmospheric and oceanic circulation patterns in the Mollisol region of Northeast China is crucial for preventing and controlling soil erosion in the context of frequent extreme precipitation events. [Methods] Four water erosion dynamic factors, including rainfall erosivity (R), heavy rainfall (R50p), very wet day precipitation (R95p) and the maximum five-day rainfall (R5d), were selected to characterize water erosion dynamic factors. Based on daily rainfall data from 1960 to 2020, the spatial and temporal patterns of the water erosion dynamic factors in the Chinese Mollisol region in 1960—2020 were analyzed using the moving average, wavelet analysis, Sen's method and Mann-Kendall test methods, and the responses of water erosion dynamic factors to atmospheric and ocean circulation patterns were analyzed. [Results] (1) The annual rainfall erosivity R varied from 1 145.36 to 3 575.94 (MJ·mm)/(hm²·h·a), heavy rainfall amount R50p was between 73.17 and 197.86 mm, very wet day precipitation R95p varied from 265.81 to 566.35 mm, and maximum five-day rainfall R5d varied from 69.67 to 124.95 mm in the Chinese Mollisol region from 1960 to 2000. (2) These water erosion dynamic factors in the study region did not show a significantly increasing trend over the past 61 years and did not show an overall abrupt change, but a noticeable upward trend was observed after 2015, which hinted that potential risk of rainfall erosion could rise in the near future. Moreover, the water erosion dynamic factors displayed periodic changes with a main cycle of approximately 44 years and a secondary cycle of 29 years, and they went through two oscillatory processes with high and low levels. (3) The spatial distributions of these water erosion dynamic factors showed high values in the south and central parts, and low values in the north, east and west parts. The maximum values occurred in the Changbai-Wanda hilly area, while the minimum values were in the Hulunbeier hilly plain area. (4) In addition, the East Asian Summer Monsoon Index (EASMI) was the most important single circulation pattern affected the water erosion dynamic factors, while the Arctic Oscillation (AO) and Multivariate ENSO Index (MEI) could indirectly affect the water erosion dynamic factors in the Chinese Mollisol region by influencing the East Asian summer monsoon. The superposition of the East Asian Summer Monsoon Index and the South China Sea Monsoon Index (EASMI-SCSSMI) had the most significant impact on water erosion dynamic factors (ΔPSAC>5%), while three circulation patterns of the East Asian Summer Monsoon Index, the South China Sea Monsoon Index and the Multivariate ENSO Index only significantly affected rainfall erosivity R(ΔPSAC>5%). [Conclusion] The factors that influence the spatial and temporal patterns of water erosion dynamics in the mollisol region of northeast China included topography, East Asian summer monsoon and South Asian summer monsoon, etc. Additionally, it is essential to be aware of the potential water erosion that may occur due to the rebound of water erosion dynamics after 2014.

Abstract:[Objective] To scientifically identify the types of soil erosion at the watershed scale and give the corresponding probability of occurrence. [Methods] This study constructs a deep learning (DL)-based model for calculating soil erosion modulus in the Songhua River Basin and calculates different types of soil erosion modulus. Using three erosion modulus influencing factors, namely rainfall, air temperature and wind speed, as random variables, numerical simulation and Gaussian Kernel Density Estimation (GKDE) were used to construct the EM probability evaluation method, which gives the probability of occurrence of different combinations of soil erosion intensities. [Results] The R² of the validation period of the EM computational models were all >0.86; 74.47% of the average annual occurrence of slight water erosion and slight wind erosion in the watershed; 12.86% of the area of slight and above water erosion and slight wind erosion; 12.56% of the area of slight and above wind erosion and slight water erosion; 0.11% of the area of water erosion strength and wind erosion intensity are both slight and above. 36 typical image elements of the 36 typical images, the average probability of occurrence of slight water erosion and slight wind erosion is 57.45%; the average probability of occurrence of slight water erosion and mild wind erosion is 30.26%; the average probability of occurrence of slight water erosion and moderate wind erosion is 8.03%; the average probability of occurrence of mild water erosion and slight wind erosion is 2.11%; the average probability of occurrence of slight water erosion and severe wind erosion is 2.08%; and the evaluations of occurrence of the remaining combinations of probabilities were all below 0.05%. [Conclusion] The calculation model of erosion modulus in the Songhua River basin constructed in this study has high accuracy, reveals the spatial distribution characteristics of soil erosion types in the Songhua River basin, and gives the probability of occurrence of different combinations of the intensity of the two types of erosion, which provides a basis for the management of soil erosion in the Songhua River basin.

Abstract:[Objective] Exploring the drought resistance characteristics of Pinus tabulaeformis, a major afforestation tree species for soil and water conservation, under different water stress to provide a scientific basis for the management of P. tabulaeformis artificial forests in the region. [Methods] Using one-year P. tabulaeformis seedings as the research subject, four levels of water stress treatments were set up, which were control group (CK), mild stress (RE25%), moderate stress (RE50%) and severe stress (RE75%), respectively, the growth characteristics, hydraulic function and osmotic regulatory substance content of P.tabulaeformis seedlings were analyzed after different water stress treatments, and their correlation was analyzed. [Results] (1) Compared with the CK treatment, after twenty months of RE50% and RE75% treatment, the aboveground biomass of P. tabulaeformis significantly decreased by 19.1% and 37.0%, respectively, while the underground biomass significantly increased by 13.7% and 23.9%, respectively. (2) In the CK, RE25%, RE50% and RE75% treatments, the water potential threshold for embolism resistance of P. tabulaeformis new branches was -1.43, -2.04, -0.91 and -0.58 MPa, respectively. (3) Compared with CK, in the RE50% and RE75% treatments, the soluble sugar content in the coarse roots significantly increased by 123.3% and 121.9%, respectively, the starch content significantly increased by 15.0% and 58.0%, respectively, and the total nonstructural carbohydrate (NSC) content significantly increased by 104.0% and 83.2%, respectively. In the RE75% treatment, the proline content in the new branches significantly decreased by 43.0%, while the K⁺ content decreased by 23.7% compared with the CK group. (4) The contribution rates of various osmotic regulating substances in various organs to hydraulic function under different water stress were as follows: NSC, starch, soluble sugars, K⁺, proline and soluble sugars in tracheid sap. [Conclusion] Mild water stress could enhance the embolism resistance of new branches. P. tabulaeformis seedlings maintained their metabolism by increasing root carbon storage. Meanwhile, the numerous organs of P. tabulaeformis improved cell concentration, reduced osmotic potential, and preserved hydraulic function to adapt to water stress environment by coordinating the accumulation of osmotic regulating substances. This study advanced the understanding of P. tabulaeformis' drought resistance mechanism and provided a scientific basic for the management of P. tabulaeformis artificial forests on the Loess Plateau.

Abstract:[Objective] The rich and coarse sediment areas of middle Yellow River basin is a typical ecologically fragile area in China. Accurately quantifying the spatiotemporal dynamic changes of cropland in this region is crucial for evaluating regional food security, ecological restoration benefits, soil erosion conditions, and the downstream tranquility of the Yellow River. [Methods] Based on five high-resolution (30 m) land use/cover dataset products (CNLUCC, GLC_FCS30, CLCD, AGLC-2000-2015, GlobeLand30), this study employed methods such as cropland dynamic degree, deviation coefficient, transfer matrix, and spatial consistency analysis to comparatively analyze the spatiotemporal characteristics of cropland in the rich and coarse sediment areas. A high-precision fused dataset with a 30 m resolution was formed and validated. Based on this fused product, an analysis of the quantity, distribution, and structural characteristics of cropland in rich and coarse sediment areas of middle Yellow River basin in 1990—2020 years was conducted. [Results] There are significant differences in cropland characteristics among existing multi-source dataset products, with the fused products demonstrating higher accuracy compared to using any of the five existing products individually. Analysis based on the fused products reveals a trend of initially increasing followed by fluctuating decline in cropland area in 1990—2020, with the implementation of the Grain for Green project serving as a turning point. In 1990—2020, there has been a net decrease of 3 170.59 km² in cropland area, representing a reduction of 17.63%. Furthermore, the proportion of cropland with slopes greater than 15° has been decreasing annually. The main types of dynamic transfer of cropland are into grassland, followed by artificial surfaces. The implementation of ecological projects such as the Grain for Green program, along with urbanization construction, is the primary cause of the decrease in cropland. [Conclusion] Researchers are encouraged to comprehensively analyze the strengths and weaknesses of multi-source products based on their research objectives. Exploring effective methods for fusing and interpreting multi-source data, with a focus on target land classes, can lead to a more in-depth understanding of the land characteristics in a specific region and, consequently, more precise research conclusions.

Abstract:[Objective]Tuojiang River Basin is facing serious ecological and environmental problems such as soil erosion, water environment pollution and soil erosion. It is of great significance to carry out the evaluation of the ecological and environmental quality of this basin in order to promote the ecological environmental protection of the upper reaches of the Yangtze River and the high-quality sustainable development of the basin's socio-economy. [Methods] Based on the Google Earth Engine platform, Landsat remote sensing images from 2000 to 2020 were selected to construct an ecological environment quality evaluation model with NDVI, WET, LST, NDBSI, and AI indices, and the coefficient of variation, one-way linear regression, and spatial autocorrelation analysis methods were used to analyze the spatial and temporal evolution pattern of ecological environment quality in the watershed, and to detect the driving force using the optimal parameter Geographic Detector Model(OPGD). [Results] (1) During the period of 2000—2020, the multi-year average value of ecological environmental quality in the Tuojiang River Basin is 0.66, and the grade is mainly good, accounting for 63.01%. The ecological environment quality in the surrounding districts and counties of Chengdu, Neijiang, Zigong, Luzhou and other towns and regions is poor, showing a spatial distribution pattern of low north-south and high middle. (2) The ecological environment quality of the Tuojiang River Basin is generally on a declining trend, and the trend of deterioration of ecological environment quality is significant, with the ratio of slightly degraded and significantly degraded areas being 19.75% and 5.88%. The urbanized areas with high population density and high level of socio-economic development are dominated by higher fluctuations in ecological environment quality, accounting for 18.15%. (3) The global autocorrelation Moran index of Tuojiang River Basin during 20 years ranged from 0.769 to 0.870, which was mainly distributed in the first and third quadrants, and the ranges of local autocorrelation high-high agglomerations and low-low agglomerations showed significant changes over time, with obvious fragmentation of the landscape patches. (4) The OPGD results show that land use type, slope, elevation, and nighttime lighting are the main drivers of ecological quality change in the watershed, population density, temperature, and GDP are secondary drivers, and precipitation and slope orientation factors are less influential. Land use type interacted with other factors to enhance the influence on the change of ecological environment quality in the watershed. [Conclusion]The improved remote sensing eco-index model provides a new method for regional ecological environment quality evaluation, and the results of the study provide a reference for ecological environment protection.

Abstract:[Objective] Analyzing the spatial and temporal evolution characteristics of ecological land use in Urumqi city, especially identifying the conflict areas between construction land expansion and ecological land use, is of great significance for the protection of ecological land use, optimization of ecological security pattern and sustainable development of the region in arid zone oasis cities. [Methods] Based on the land use data of Urumqi city in 2000, 2010 and 2020, the spatial conflict between construction land expansion and ecological land use in Urumqi city was analyzed by using the attitude of land use dynamics, the speed and pattern of construction land expansion, identifying ecological sources and constructing a spatial pattern of ecological security. [Results] (1) From 2000 to 2020, the areas of forest land, grassland, watershed and construction land in the study area showed an overall increasing trend, increasing by 160.51, 451.17, 47.58, and 805.19 km² respectively, while the areas of cultivated land and unutilized land continued to decline. (2) The accelerated expansion of construction land area in the study area was the most significant in Middong district, with a total increase of 230.62 km², and the smallest expansion of construction land area in Tien Shan district. (3) In 2000—2020, the overall ecological level of Urumqi has shown an upward trend, and the area of ecological sources has increased by a total of 611.52 km². (4) The area of spatial conflict between construction land expansion and ecological land use is the largest in Urumqi county, followed by Midong, Shayibak and Shuimogou districts, while the new urban area is a spatial conflict-free area. [Conclusion] The results of the study show that there is a spatial conflict between construction expansion and ecological land use in Urumqi during 2000—2020.

Abstract:[Objective] This study is aiming to evaluate the dynamic evolution of soil microstructure stability during vegetation restoration on the Loess Plateau. [Methods] Soil samples from four stages of vegetation succession in the Ziwuling forest region were examined. Utilizing the amplitude sweep test method, soil shear strength and viscoelastic parameters were assessed under various matric potentials (0, -3 and -10 kPa). Correlation analyses between these parameters and soil physicochemical properties were conducted. [Results] (1) Soil shear strength and viscoelasticity exhibited an increasing trend with advancing vegetation succession stages, attributed primarily to the increasing of soil organic carbon, exchangeable Ca²⁺ and sand content, along with reduced Na⁺ during vegetation recovery. This augmentation contributed to enhanced interparticle adhesion and frictional forces. (2) The soil shear strength parameter increased with the decreasing of matric potential. Under low matric potential conditions, there was no significant correlation between soil shear strength parameters (G'_LVE、τ_LVE and τ_max) and exchangeable Ca²⁺ and sand content. Under high matric potential conditions, soil shear strength parameters showed a significant positive correlation with exchangeable Ca²⁺ (p<0.05), while τ_max, G'_LVE, τ_YP, and G'_YP exhibited significant positive correlations with sand content. (3) Soil viscoelastic parameters (γ_YP and I_z) showed a decreasing trend with declining matric potential. Particularly, under high matric potential conditions, these parameters exhibited a positive correlation with organic carbon content, which gradually attenuated with the decreasing of matrix potential. Viscoelastic parameters were negatively correlated with clay content under different matric potentials. (4) The overall mechanical stability of soil was positively correlated with soil Ca²⁺ at 0 kPa, negatively correlated with soil silt and K⁺ content at -3 kPa, and positively correlated with clay content at -10 kPa. [Conclusion] The changes and influencing mechanism of soil mechanical stability under different vegetation types and different matric potentials were revealed, which provided an important basis for understanding the evolution of soil characteristics in the process of vegetation restoration on the Loess Plateau, and also provided theoretical support for soil protection and ecological restoration in the future.

Abstract:[Objective] To determine the effect of biological soil crusts (biocrusts) on water evapotranspiration of the shrub-grass ecosystem. [Methods] The effect of biocrusts on water evapotranspiration of the shrub-grass ecosystem in water-wind erosion crisscross region of Loess Plateau was investigated by using original soil columns of field condition. In the study, the bare soil column was used as control, and three treatments were set up. The three treatments were shrub-grass (single plant shrub-20% grass), shrub-grass-30% biocrusts and shrub-grass-50% biocrusts. [Results] The results showed that after 12 hours of simulated 30 mm precipitation infiltration, water content of 0—20 cm soil layer in the shrub-grass-biotic crust treatment was 15.4% higher than that in the bare soil treatment and 12.8% higher than that in the shrub-grass treatment. Compared with bare soil, soil water evapotranspiration of shrub-grass and shrub-grass with two level of biocrusts’ coverage significantly increased. Among them, soil water evapotranspiration of shrub-grass treatment increased by 120.3% compared to bare soil, while shrub-grass-biocrusts increased by 116.5% on average. Biocrusts reduced soil water evapotranspiration of the shrub-grass ecosystem. Compared with the shrub-grass treatment, soil water evapotranspiration of the shrub-grass-biocrusts decreased by 1.7% on average. The degree of reduction of evapotranspiration was related to the coverage of biocrusts, period and soil depth. Among them, the water evapotranspiration of shrub-grass-50% biocrusts was 13.4% lower than that of shrub-grass-30% biocrusts. The reduction of water evapotranspiration of shrub-grass ecosystem caused by biocrusts was obvious during the first 1~4 days after rain. The reduction of water evapotranspiration of shrub-grass ecosystem caused by biocrusts mainly related to the evapotranspiration of 20—45 cm soil layer. Compared with the shrub-grass treatment, the water evapotranspiration loss of the 0—20 cm soil layer of the shrub-grass-biocrust treatment increased by 14.4% on average, while the water dissipation below 20 cm decreased by 15.5% on average. [Conclusion] Under the condition of 30 mm rainfall, biocrusts reduced the water evapotranspiration of shrub-grass ecosystem, which may beneficial the water deficit of shrub-grass vegetation in the wind-water erosion crisscross area. The study provides a reference for revealing the effect of biocrusts on water evapotranspiration in shrub-grass ecosystems.

Abstract:[Objective]In order to explore the effects of different land use patterns on soil physicochemical properties in the Loess Plateau area. [Methods]This study used bare land as a control (CK), and set four different use patterns as conventional fertilization farmland (H), unfertilization farmland (L), and alfalfa grassland (A) in Changwu, Shaanxi Province since 2005. The physical and chemical properties of 0—200 cm soil in the four plots were determined in July 2021. [Results] After 17 years, there were significant differences between farmland and grassland on soil physicochemical properties. (1) In 0—40 cm soil surface, the volume fraction of clay and powder in alfalfa field slightly increased compared with the other three plots, the volume fraction of sand slightly decreased, while the proportion of clay and fine powder in bare field decreased. (2) In the 0—20 cm of the soil, compared to bare land, soil pH significantly increased by 0.8% in alfalfa grassland, and significantly decreased by 1.7% in fertilized farmland. Except for 80—100 cm, soil pH in 0—200 cm section of fertilized farmland was significantly lower than that in the other three plots. Compared with bare land, in the 0—20 cm of the soil, the organic carbon storage, organic matter and nitrogen content of alfalfa grassland and fertilized farmland increased significantly and the contents of them from alfalfa grassland was higher than those of fertilized farmland. The content of available phosphorus and available potassium of alfalfa grassland and unfertilized farmland decreased significantly. The content of available potassium of fertilized farmland also decreased significantly. The content of alkaline dissolved nitrogen and nitrate-ammonium nitrogen of unfertilized farmland decreased significantly. (3) Under different land use patterns, soil organic matter, organic carbon and total nitrogen showed a decreasing trend from 0 to 60 cm, then an increasing trend showed until it reached 100 cm depth and after where a decreasing trend showed again with the deepening of the soil layer. The available phosphorus content of the soil in grassland gradually increased after 60 cm. The vertical distribution of other nutrient indexes in 0—200 cm space showed a downward trend. (4) There was a significant positive correlation between soil organic matter, total nitrogen, alkaline dissolved nitrogen and nitrate-ammonium nitrogen at 0—100 cm, and a significant negative correlation between available phosphorus and organic matter, total nitrogen, alkaline dissolved nitrogen and pH. There was a significant positive correlation between soil organic matter and available potassium at 100—200 cm, and a significant negative correlation between available phosphorus and pH. [Conclusion] Reasonable farmland management and continuous planting of alfalfa in the Loess Plateau area can keep the nutrient indexes of organic matter, total nitrogen and available nitrogen at a high level, which can guarantee soil quality to a certain extent. In order to promote the sustainability of soil in this region, it is recommended to increase the input of potassium fertilizer and organic fertilizer in farmland, while the grassland needs to supplement the appropriate amount of phosphate and potassium fertilizer.

Abstract:[Objective] To explore the dynamic changes in the environmental quality of the Qinghai-Xizang Plateau and provide reference for ensuring the ecological security of the Qinghai-Xizang Plateau, protecting biodiversity and building a strong ecological barrier.[Methods] Based on five periods of land use data in 1985, 1995, 2005, 2015 and 2022, with the help of the InVEST model, we quantitatively assessed the habitat quality status of the Qinghai-Xizang Plateau in 1985—2022 and analyzed its spatiotemporal pattern. Finally, we used bivariate spatial autocorrelation explore the spatial response of habitat quality to climate change and human activities. [Results] (1) In 1985—2022, the habitat index of the Qinghai-Xizang Plateau has increased by 0.052 9, and the proportion of higher and higher habitat areas has increased by 5.51% in total, the overall habitat quality level has improved but is still at a low level. (2) In 1985—2022, the habitat quality of most areas on the Qinghai-Xizang Plateau has increased by 48.14%, but the overall spatial distribution of habitat levels has not changed much, and each level area has increased in nested levels from outside to inside. (3) In 1985—2022, the main types of environmental quality grade transfer in the Qinghai-Xizang Plateau have remained unchanged, but the intensity of grade transformation has continued to increase. (4) In 1985—2022, the habitat quality of the Qinghai-Xizang Plateau has a significant spatial correlation with climate change and human activities, the average annual temperature has a significant spatial negative correlation with the habitat quality, the annual precipitation and human activity intensity have a significant spatial correlation with the habitat quality, there is a significant positive spatial correlation. [Conclusion]The research results reveal the spatiotemporal evolution characteristics of the Qinghai-Xizang Plateau's habitat quality, and clarify that climate change and human activities have a profound impact on habitat quality. In the future, bottom-line constraints and human activity guidance should be strengthened.

Abstract:[Objective] Exploring the water-holding function is an important way to cope with future climate change. Existing research mainly focuses on the assessment of historical and current water-holding function, and lacks the understanding of the future water-holding function, which limits the value of guiding the sustainable development and dynamic management of the region. [Methods] Taking Yunnan Province as an example, this paper combined the system dynamics model, patch-level land use change simulation model (PLUS model), and InVEST model to build a water conservation evaluation framework under the impact of future climate and land use change. The framework can predict land use change and assess water conservation in the context of future climate change and different economic developments. Water conservation in Yunnan Province was evaluated based on the coupling scenarios of three shared socioeconomic paths and typical concentration paths (SSP1-1.9, SSP2-4.5, SSP5-8.5). The main driving factors of temporal and spatial changes in water conservation in Yunnan Province were identified by using the optimal parameter geodetector. [Results] (1) From 2000 to 2030, the total area of cultivated land and unused land decreased, the area of water area and construction land increased gradually, and the forest land and grassland changed in a wavy line; The trend of land use change in different scenarios is roughly the same, namely: grassland > construction land > cultivated land > unused land > water area > forest land. (2) From 2000 to 2020, water conservation showed a gradually decreasing trend, decreasing by 2.27×10⁹m³; Under the influence of different climate and land use models, the water conservation under different scenarios is different, and the water conservation under the SSP2-4.5 scenario is the highest, which is 9.338×10⁹m³. The spatial distribution pattern is "high in the southwest and low in the northeast". (3) The results of geographical detection show that the average annual precipitation, soil type, and DEM are the main driving factors affecting the spatiotemporal distribution difference of water conservation, and the interaction between precipitation and other factors is significantly enhanced. [Conclusion] According to the temporal and spatial differences in water conservation in Yunnan Province, different suggestions were put forward in this study to provide scientific reference for ecosystem service research and sustainable development route planning in Yunnan Province.

Abstract:[Objective] In order to explore the effect of corn straw biochar on water infiltration characteristics of calcareous soil in southwest karst area. [Methods] Five biochar application gradients (0, 2%, 4%, 6%, and 8%), three gravel content soils (10%, 20%, 30%) and no gravel soil were set up to carry out one-dimensional water infiltration test. [Results] (1) With the increase of biochar application rate, except for 10% gravel content, the migration depth of the wetting front gradually decreased, and the inhibition effect of adding biochar on gravel soil was weaker than that on non-gravel soil. Taking 60 min as an example, compared with CK (without gravel), it was reduced by 10%~27%, and the three gravel conditions were reduced by 1%~17%, 1%~16%, and 1%~21%, respectively. When the application amount was 8%, the migration depth of each treatment was the smallest. (2) Biochar reduced the cumulative infiltration of lime soil. The cumulative infiltration amount without gravel was 9%~27% lower than that of CK, while that with gravel was 11%~21% lower than that of CK. Among them, the cumulative infiltration amount was the least when the amount of gravel and biochar was 30% and 8%, respectively, and the amount of 2% had no significant effect. (3) With the increase of biochar application rate, the initial infiltration rate and stable infiltration rate of gravel-free soil decreased gradually. The effect of biochar on the stable infiltration rate of gravel soil is more significant than the initial infiltration rate. (4) Compared with the Philip model, both the Horton and Kostiakov models can be used to fit the soil water infiltration process in this study, but the fitting trend of the Horton model is more consistent with the actual results. [Conclusion] Corn straw biochar presents a promising solution for mitigating soil water infiltration in calcareous soil within karst regions. The distinguishing factor lies in the observation that the efficacy of corn straw biochar in mitigating soil water infiltration is less pronounced under gravel-infused conditions compared to homogeneous soil devoid of gravel. These findings offer valuable insights for the regulation of rainfall infiltration and effective soil moisture management in limestone-rich soils across the southwest karst landscape.

Abstract:[Objective] The transportation of sediment via glacial meltwater can not only reflect the glacial erosion and landform evolution, but also is one of the important sediment sources for the downstream river. Thus, understanding the suspended sediment and bedload dynamics in glacier meltwater runoff on the Tibetan Plateau is significant for predicting glacier landform evolution and conducting downstream disaster prevention and mitigation efforts. [Methods] To achieve the goal, the variations of flow discharge, sediment concentration of suspended load, and bed load transport rate per unit width were monitored at the downstream channel of Qiyi Glacier in the Qilian Mountains from August 11 to 24, 2023. Based on the observed data, the relationship curves of flow discharge-water level, sediment concentration of suspended load-flow discharge, and unit bed load transport rate-flow shear stress were developed to obtain the variations of both water flow and sediment transport throughout the study period. [Results] The sediment concentration of suspended load and the bed load transport rate in the downstream channel of Qiyi Glacier are predominantly influenced by the variations in meltwater runoff, exhibiting pronounced daily fluctuations. The daily nadir of suspended sediment concentration is observed around 10:00, while the acme occurs around 16:00. The median particle size of the sediments is approximately 0.3 mm, indicating a fine-grained sediment composition. The variation trend of bed load transport rate versus time is almost the same to the suspended load, excepting at 05:00-09:00. During this period, there is no bed load in the channel since the flow shear stress is insufficient to mobilize and transport the bed load. Note that the median particle size of bed load is about 12 mm. The sediment transport in the downstream channel of Qiyi Glacier is primarily dominated by suspended sediment, and the daily sediment transport amount of bedload is much smaller than that of suspended sediment, accounting for only 1.73%~2.81% of the daily sediment transport amount of suspended sediment. Air temperature of glacier is a critical factor influencing the flow discharge of glacier meltwater, the sediment concentration of suspended load, and the transport rate of bed load. Moreover, as air temperature of glacier rises, both the flow discharge and suspended sediment concentration display linear increasing trends, while the bed load transport rate exhibits an exponential increase. [Conclusion] This implies that, in future climate change scenarios, where the flow discharge of glacier meltwater increases, the suspended and bed loads transport within the Qiyi Glacier meltwater will become more significant and deserve more attentions.

Abstract:[Objective] Soil saturated hydraulic conductivity (K_s) reflects soil infiltration capacity and erosion resistance potential, which significantly affects hydrology and erosion processes. Economic fruit forest is an important land use type in the Three Gorges Reservoir area, biological crust wide-developed under the forest, which will inevitably drive the change in soil physical and chemical properties, thereby affecting K_s, but the effect of biological crust development on soil saturated hydraulic conductivity and its driving mechanism in reservoir area is still unclear. [Methods] Therefore, in order to investigate the effect of biological crust development on K_s in the Three Gorges Reservoir area. One site without biological crust (as control) and five moss crust sites with different coverage (0~20%, 20%~40%, 40%~60%, 60%~80%, 80%~100%) were selected under the economic fruit forest. The soil saturated hydraulic conductivity and basic soil physical and chemical properties of biological crust with different coverage gradients were determined by field sampling and laboratory analysis, combined with nonlinear regression, partial least squares regression and structural equation model methods. The changes in K_s with biological crust coverage and main factors attributed to these changes were clarified. [Results] (1) The development of biological crust significantly increased K_s, and compared to control, K_s of economic fruit forest covered by 0~20%, 20%~40%, 40%~60%, 60%~80%, 80%~100% biological crust increased by 36.98%, 338.09%, 407.17%, 900.66%, 713.11%, respectively. (2) K_s increased in an approximate logarithmic trend with the increase of biological crust coverage. When biological crust coverage was greater than 60%, K_s tended to be stable. (3) K_s was significantly correlated with the biological crust characteristics and the differences in soil physical and chemical properties driven by biological crust. The thickness of biological crust, soil bulk density, total porosity, saturated water content and water-stable aggregate content were the main influencing factors leading to the differences in K_s with different biological crust coverages. (4) The result of structural equation model showed that the development of biological crust was mainly through its indirect effect in improving soil structure (indirect path coefficient 1.655 bigger than direct path coefficient 0.887) to increase K_s. [Conclusion] These results provide a theoretical basis for understanding the hydrologic and erosion processes of biological crust development in the Three Gorges Reservoir area, and also provide practical guidance for the prevention and controlling of soil and water loss in the economic fruit forest land.

Abstract:[Objective] In order to study the effects of different phosphorus application rates in wheat season on crop yield and phosphorus fertilizer efficiency in different crop rotation systems in Guanzhong area of Shaanxi Province, the appropriate phosphorus fertilizers application rates in wheat season were defined to achieve high yield and high efficiency of crops in different rotation systems. [Methods] Two crop rotation systems, wheat-maize and wheat-soybean, were selected as the research objects, and five phosphorus application rates (P₂O₅) (0, 75, 150, 225, and 300 kg/hm²) were set. The annual crop yield, phosphorus fertilizer utilization efficiency, soil available P content and their relationships with phosphorus application rates were analyzed in 2021-2022 and 2022-2023. [Results] Compared with no phosphorus application (0 kg/hm²), only phosphorus application in wheat season significantly increased the annual yield of wheat, maize, soybean and annual yield of wheat-maize and wheat-soybean crop rotation systems (p<0.05), and the annual yield and phosphorus fertilizer efficiency of crop rotation reached a high level. The annual yield of the two crop rotation systems was the highest in the 150 kg/hm² treatment, and the wheat-maize crop rotation system was significantly higher than the 75 kg/hm² treatment (p<0.05), but there was no significant difference between wheat-soybean crop rotation and 75 kg/hm² treatment. The soil available P content of the wheat yield of wheat-maize and wheat-soybean crop rotation systems was 20.07, 16.15 mg/kg, respectively. The agronomy efficiency, partial productivity, recovery rate and phosphorus efficiency index (PEI) of phosphorus fertilizer in the two crop rotation systems decreased with the increase of phosphorus application rate. The PEI of wheat-maize and wheat-soybean rotation systems with 75 kg/hm² P application were 1.24, 2.02 times of 150 kg/hm² P application, respectively, and the PEI of wheat-soybean rotation system decreased more significantly. Considering food security, environmental security and fertilizer utilization rate, and taking 95% of the maximum wheat yield as the actual target, the corresponding P application rates of wheat-maize and wheat-soybean rotation systems were 115, 95 kg/hm², respectively, which could achieve phosphorus recovery efficiency and low phosphorus surplus, and ensure that the annual yield of wheat-maize and wheat-soybean rotation systems reached 96.23% and 95.43% of the maximum yield, respectively; the wheat-soybean rotation system had a lower P application requirement. [Conclusion] For different rotation systems, reasonable P application should be carried out from the perspective of crop yield, fertilizer efficient utilization and zero surplus management policy, so as to meet the coordinated supply of crop-soil P nutrients to ensure high yield while improving P efficiency.

Abstract:[Objective]Soil cracks can change soil structure, reduce soil stability, and then accelerate the development of hill collapse. It is of great practical significance to study deeply the fracture development law of granite Benggang area under wetting-drying cycles. [Methods] 7 samples of granite slope soil were taken as the research objects, including the upper part of the slope (US), the middle part of the slope (MS), the lower part of the slope (DS), the red soil layer of wall collapse (RL), the transition layer of wall collapse (TL), the sand layer1 of wall collapse (SL1) and the sand layer2 of wall collapse (SL2). The wetting-drying cycles experiments were carried out with these samples. Combined with digital image processing technology, the soil surface cracks are quantitatively analyzed. [Results] (1) Soil R_sc, Na and soil fragmentation degree in granite Benggang area increase with the decrease of water content, the R_sc, N_a, W_a and L_a of 7 sample points show a gradual decrease with the increase of dry and wet alternating times. (2) The connectivity of cracks in the red soil layer in the upper part of the slope, the middle part of the slope and the sand layer of the wall collapse are significantly positively correlated with the sand content. The R_sc at each sampling point is significantly positively correlated with saturated water content, organic matter content, cation exchange capacity, and free iron oxide content. Sampling points with high clay/sand content show a significant positive correlation with clay/sand content.[Conclusion] There are differences in the development of dry shrinkage cracks in different layers of soil of granite Benggang area, but the development rules are basically three stages: preparation stage, rapid development stage and stable development stage. The cracks of red soil layer on the upper part of the slope of granite soil are mainly shrinkage cracks, and the shrinkage cracks of red soil layer in the lower part of the slope are less.

Abstract:[Objective] The Jinsha River Basin is an important ecological area in the southwestern mountainous gorge region. Predicting and assessing climate and future runoff changes in the Jinsha River Basin under the background of global warming is of great significance for soil and water conservation, flood control, disaster reduction, and water resource planning at the basin scale. [Methods] This study simulates the hydrological processes of the Jinsha River Basin using the VIC model and downscales data from 20 climate models and the Multi-Model Ensemble Average (MMEA) under two emission scenarios (SSP2-4.5, SSP5-8.5) from the CMIP6 global climate models to predict runoff trends from 2015 to 2100. [Results] (1) The historical runoff simulation indicates that the Nash efficiency coefficient between the simulated and observed values exceeds 0.6, and the absolute value of BIAS is controlled within 0.15, demonstrating that the VIC model is suitable for simulating the hydrological process in the Jinsha River Basin. (2) The hydrological process components simulated by the VIC model show that precipitation increases from the upstream to the downstream regions, evapotranspiration is higher in the middle and lower reaches, and the multi-year average values of surface runoff and base flow increase from the upstream to the downstream regions with significant differences, further validating the model's applicability. (3) A comparison of single-model and MMEA simulation results using the EEMD-based (Ensemble Empirical Mode Decomposition) statistical downscaling method reveals that the MMEA matches the observed data the best. Under future SSP2-4.5 and SSP5-8.5 scenarios, the simulation results indicate that hydrological elements change more significantly under the high-radiation and high-emission scenarios (SSP5-8.5), with a particularly noticeable increase in evapotranspiration. [Conclusion] The runoff simulations show that the annual average runoff remains relatively unchanged under the SSP2-4.5 scenario, while it shows a slightly increasing trend under the SSP5-8.5 scenario. Future monthly runoff simulations indicate that most months under the SSP5-8.5 scenario have higher runoff compared to the SSP2-4.5 scenario.

Abstract:[Objective]To reveal the vertical distribution characteristics of soil organic carbon, nitrogen, and phosphorus content, soil stoichiometric characteristics (C/N, C/P, N/P), enzyme activity, microorganisms, and their seasonal responses of forest stand types in Liziping Nature Reserve. [Methods]The soils of Cyclobalanopsis and populus szechuanica broad-leaved mixed forest, Oriental oak deciduous broad-leaved forest, Fir-spruce coniferous mixed forest, and Yushania lineolata forest in the dry and rainy seasons were selected as the study objects to elucidate the effects of forest stand types on the stoichiometric characteristics of the soils, the enzyme activities, the microorganisms, and their seasonal dynamic response characteristics. [Results] (1) The soil physicochemical properties and enzyme activity of the four forest stand types are higher in the rainy season than in the dry season. (2) The soil C/N in the Cyclobalanopsis-populus szechuanica broad-leaved mixed forest is higher in the dry season than in the rainy season, while the other three stands show the opposite trend. Dry season's C/P are higher than the rainy season in Cyclobalanopsis and populus szechuanica broad-leaved mixed forest and Fir-spruce coniferous mixed forest, while the other two stands are the opposite.Dry season's N/P are higher than the rainy season in Oriental oak deciduous broad-leaved forest and Fir-spruce coniferous mixed forest, while the other two stands are the opposite. (3) Different forest types' value variation of soil C/N, C/P, and N/P are 17.00~37.33, 62.72~114.50, 3.09~5.18 in the dry season, and 17.72~39.16, 63.21~90.72, 2.39~5.80 in the rainy season. (4) The C/N and C/P values during the dry and rainy seasons are higher than the national average (11.90, 61.00), indicating that nitrogen is limited during nutrient cycling and the potential for releasing P is low; The N/P values for both seasons were lower than the national average soil level (5.20), indicating that the soil is more susceptible to N limitation; (5) The soil microbial activity of the four forest stand types is better in the rainy season than in the dry season, and the soil ecological stoichiometric characteristics are mainly influenced by enzyme activity and microorganisms. [Conclusion] The results of this study can provide important theoretical basis for exploring the seasonal response mechanisms of regional soil nutrient decomposition, supply and limitation, as well as nutrient cycling processes.

Abstract:[Objective] In order to quantitatively analyze the response mechanism of agricultural drought to single factor in karst areas. [Methods] In this study, Delaunay triangulation and K-means clustering were employed to calculate the area and classify the annual rainfall data of 83 stations in Guizhou Province, resulting in the division of Guizhou into 5 regions. Subsequently, a vector autoregressive (VAR) model was established based on the meteorological factors including precipitation (Pre), average temperature (T), potential evapotranspiration (E), wind speed (W), air pressure (P), soil moisture content (SW), and standardized soil moisture index (SSI) for each region. The response mechanism of agricultural drought to various time scales of meteorological factors and soil moisture content was analyzed using pulse response and variance decomposition. [Results] (1) The agricultural drought was higher in the west and lower in the east, and gradually decreased from south to north; The agricultural drought is more severe in spring and summer than in autumn and winter. (2) The time required for the impulse response of each variable on the annual scale to reach the peak of SSI is Pre＜E=W＜P＜SW＜T, and the recovery period is Pre＞W＞T＞E＞P＞SW. From the monthly scale to the annual scale, in areas with strong karst development, the time required for SSI pulse to reach its peak value is shortened by 2 periods for factor E; while SW is opposite to this, and the non-karst area has a shorter recovery period than karst area. (3) Rainfall plays a dominant role in agricultural drought, and rainfall and wind speed played a stronger role in agricultural drought with the increase of time scale. The contribution ratio of agricultural drought was 31.88%, 34.25%, 58.33%, 1.07%, 3.15% and 12.88%, respectively. [Conclusion] The research results can provide a theoretical basis for the early warning of agricultural drought in karst areas.

Abstract:[Objective] In order to accurately estimate net primary productivity (NPP) of vegetation under the context of rising atmospheric CO₂ concentrations. [Methods] A CO₂ concentration factor was introduced into the Carnegie-Ames-Stanford Approach (CASA) model to simulate the maximum light use efficiency of different vegetation types. Based on this, the potential of the improved model for NPP estimation was explored. [Results] From 2000 to 2020, the annual average atmospheric CO₂ concentration in China's terrestrial areas showed a significant increasing trend, with an average increase of approximately 2.14 μmol/(mon·a). After incorporating the CO₂ stress factor, the vegetation types were ranked by maximum light use efficiency in the following order cropland>evergreen broadleaf forest>mixed forest>needleleaf forest>shrub>wetland>grassland (1.85, 1.69, 1.30, 0.87, 0.52, 0.40, 0.40 g/MJ). The estimation accuracy of NPP by the CASA_CO₂ model was improved compared to the original CASA model. The R² between the simulated and measured NPP values at the vegetation level and the comprehensive level increased by -0.1% to 3.7% and 0.5%, respectively, and RMSE decreased by 0.3% to 9.2% and 0.7%, respectively. The RMSE of annual NPP estimation results decreased by 1.9%. The CASA_CO₂ model improved the underestimation of overall NPP by the CASA model, reducing it from 10.62% to 9.81%. The CASA_CO₂ model underestimated the overall NPP for spring, autumn, and winter by 5.11%, 2.72%, and 2.51%, respectively, while overestimating it for summer by 0.53%. [Conclusion] Considering the impact of CO₂ concentration changes on vegetation in the model can improve the accuracy of NPP estimation.

Abstract:[Objective] In order to explore the effects of canopy structure changes on rainfall distribution characteristics under different seasons and rainfall types. [Methods] Taking karst typical shrub forest as the research object, three 10 m×10 m plots were selected to remove 30% (TC₃₀) and 10% (TC₁₀) vegetation, respectively, and no exclusion (TC₀) was used as the control to monitor the throughfall and stemflow of each sample plot after removal in the dry and rainy seasons. [Results] The throughfall rate of each sample plot was 72.3%~96.6% under different rainfall types in the dry and rainy season, and there was no significant difference in the throughfall rate of each sample plot under different rainfall types or exclusion ratios. However, the stemflow rate was TC₀ (5.6%~13.9%)> TC₁₀ (4.8%~8.1%)> TC₃₀ (2.1%~6.1%) in both dry and rainy seasons, and there were significant differences under moderate rainfall in dry season, heavy rain in rainy season and heavy rain in rainy season (p<0.05). In addition, compared with TC₀ and TC₁₀, TC₃₀ had the highest rainfall input (throughfall + stemflow) in both the dry and rainy seasons (98.9% and 94.8%, respectively). [Conclusion] The removal of vegetation has no obvious effect on the throughfall rate, but can significantly reduce the stemflow rate, and appropriate forest thinning can increase rainfall input, increase soil and vegetation water availability, and improve the rainfall-soil water conversion efficiency, which can provide a reference for improving the rainfall resource use efficiency in karst areas.

Abstract:[Objective] To investigate the effects of coniferous and broadleaf mixture measures on the stability of soil carbon47 pools in Pinus Massoniana Plantation in red soil erosion areas. [Methods]In this study, we examined the impact of forest restoration on soil organic carbon fractions in the Pinus massoniana pure forest (CF) and Pinus massonianaand Schima superba mixed forest (MF) in Changting, Fujian Province. We analyzed soil profiles from different years (Y10, Y20, and Y41) by categorizing soil organic carbon into particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). [Results] (1) Compared with CF, the contents of MAOC, SOC, and POC in the 0—10 cm soil layer in mixed forest significantly increased. The long-term stand mixing effectively avoided the depletion of MAOC in long-term restoration of pine forest. (2) POC/SOC in the 10—20 cm and 40—60 cm and 0—20 cm soil layers in Y20-MF and Y41-MF decreased significantly after coniferous and broadleaf mixture, but MAOC/SOC in the 20—60 cm and 0—10 cm soil layers in Y10-MF and Y41-MF increased significantly; (3) MAOC/SOC was observed in the 20—60 cm soil layer, while in Y41-MF, it was found in the 0—10 cm soil layer. Additionally, in mixed forests, MAOC/SOC in the 0—10 cm soil layer continued to increase with age, whereas POC/SOC decreased significantly. The opposite trend was observed in the masson pine forests. (4) Linear fitting revealed that POC and MAOC were both significantly and positively correlated with SOC, but the increase in SOC in mixed forest soils were more dependent on the increase in MAOC, whereas the masson pine forests soil was more dominated by the non-stable carbon component (POC); (5) Redundancy analysis indicated that DOC, TN, TP, and NH⁺₄ collectively explained 66.2% of the variation in carbon fractions. This suggests that the enhancement of soil nutrient effectiveness following the forest conversion is crucial for MAOC accumulation in mixed forests.[Conclusion] This study demonstrates that forest conversion in subtropical red soil erosion areas could increase the accumulation of stabilized carbon pools by enhancing soil nutrient effectiveness. This process helps avoid the loss of soil carbon pools during long-term restoration efforts.

Abstract:[Objective] Qinling-Bashan mountains are not only an important ecological function area, but also a concentrated contiguous poverty-stricken area in China. It is of great practical significance to strengthen the ecological sensitivity evaluation and reveal the terrain gradient characteristics for the delineation of ecological red line and the construction of regional ecological highlands in the mountainous area. [Methods] Based on the data of land use / cover, climate, terrain and soil type, the linear weighted sum method, entropy weight method and spatial overlay analysis method have been used to evaluate its ecological sensitivity, and the sensitive function zoning and ecological protection countermeasures have been put forward. [Results] (1)The ecological sensitivity fluctuated in Qinling-Bashan mountains during 2000—2018 and it decreased after 2010;(2) Horizontally, the ecological sensitivity of Bashan mountains is higher than that of Qinling mountains;(3) Vertically, with the increase of terrain,it shows the trend of"first increasing-decreasing-then increasing".The ecological sensitivity is the highest around 900 m of elevation, and the distribution area of ecological sensitivity above severe degree is the most extensive in 75 ~ 200 m of surface cutting depth and 15° ~ 25° of slope.(4) According to the evaluation results, it is divided into five types: key construction area, moderate development area, soil-and-water conservation area, general ecological area and important ecological area, and their characteristics and protection countermeasures have been summed up and put forward. [Conclusion] In the future, we should continually optimize the land use pattern, strengthen the comprehensive management and ecological restoration of mountains, forest, farmlands, lakes and grasslands.

Abstract:[Objective] The specific mechanism of influence of low molecular weight organic acids in root exudates on metal cation release in purple soil in Yuanmou dry and hot river valley of Yunnan Province was explored to fill the current research gap and provide scientific basis for understanding soil weathering and plant-soil interaction. [Methods]The organic acid leaching test was employed to investigate the structural disintegration characteristics of purple soil under various low molecular weight organic acids and the release kinetics of ions during weathering. The quantitative analysis of the relationship between release rate and time was conducted, and the influence of different organic acids on CIA (chemical index of alteration) was discussed.[Results] Application of organic acids leads to a substantial increase in CIA value for purple soil weathering products ranging from 7.25% to 15.42%. Citric acid, at equivalent concentrations, demonstrates greater efficacy in accelerating weathering compared to oxalic acid. Scanning electron microscopy (SEM) results reveal that organic acids induce structural damage in purple soil, while MATLAB software analysis indicates that leaching by organic acids promotes the development of surface pores in soil minerals and reduces particle uniformity. The release rates of metal cations from soil vary with concentrations of low molecular weight organic acids (LMWOAs), decreasing gradually over leaching time. The metal ion release rates increase with increasing organic acid concentrations, and the total ion release pattern follows Fe³⁺ > Mg²⁺ > Mn²⁺ > K⁺ > Ca²⁺ > Na⁺. A quantitative analysis model for the metal cation release rate under changing acidity conditions is established using multivariate nonlinear regression. There exists a significant exponential function relationship between the release rate of metal cations and time. [Conclusion] The leaching of low molecular weight organic acids promoted metal cation release and weathering of purple soil, and citric acid was more significant than oxalic acid.

Abstract:[Objective] Chongqing is a mega-metropolis located in the southwestern hilly region. The rising population and extensive economic development have led to rapid urban landscape ascent and expansion, resulting in a dual urban-rural and 3D spatial structure directly influencing the landscape's configuration, functionality, and sustainability. It is urgent to conduct spatiotemporal dynamics, sloping characteristics, and future scenario predictions for regional ecological risk. [Methods] Based on the use of land use/cover data from 1990-2020 and SSPs-RCPs (2035 and 2050), integrate the landscape ecological risk assessment model, portray the time and space dynamics and climbing laws of landscape ecological risks in Chongqing, predict the ecological risk and the flows of 5 SSPs-RCPs in 2035 and 2050. [Results] (1) The ecological risk index in Chongqing decreased from 0.14 in 1990 to 0.12 in 2020, indicating an overall improvement in habitat quality. Ecological risk was higher in natural landscapes (excluding forests), compared to artificial landscapes (cultivated land and built-up land), with urban landscapes showing an increasing ecological risk trend as urban-rural density decreased. Notably, grasslands exhibited an inverse ecological risk gradient. (2) The ecological risk was low in the northeast and southeast regions of Chongqing, including the Daba and Wuling Mountainous regions. In contrast, the southwestern region and hilly river valleys had high ecological risk. Low and moderately low-risk areas accounted for over 90% of the entire region. (3) Approximately 89.4% of landscapes were distributed in areas with a slope of ≥5°, and ecological restoration efforts in ecological barrier zones with a slope of >7.5° significantly reduced risks associated with steep slope erosion or rocky desertification. (4) Comparing ecological risks and spatial transition scenarios for 2035 and 2050 under different SSPs-RCPs, SSP1 demonstrated the most sustainable development pathway. The climbing and spreading of urban landscapes would lead to increased ecological risk, while effective risk reduction can be achieved through the management and restoration of the Yangtze River riparian zone, steep slope areas in the Wuling and Dalou Mountains, and mining sites. [Conclusion] The landscapes of the mountainous metropolis are sustainable which requires science-practice-policy collaborative governance, planning and management of scientific landscapes, and cross-department and public collaboration.

Abstract:[Objective] To elucidate the differences in soil nutrient status and carbon sequestration capabilities among various vegetation types. [Methods] This study focused on six representative vegetation types in the southern mountainous areas of Ningxia: pure tree plantations (Prunus sibirica L. and Robinia pseudoacacia L.), mixed tree plantations (Robinia pseudoacacia L.+ Prunus sibirica L.), mixed tree and shrub plantations (Prunus davidiana (Carrière) Franch.+ Caragana korshinskii Kom.), shrub plantations (Hippophae rhamnoides L.), and grasslands. Through a combination of field surveys and laboratory analyses, we investigated the ecological stoichiometry and carbon storage of the 0—100 cm soil layer across these vegetation types. [Results] C, N, and P contents varied between 19.74~35.11 g/kg, 1.74 ~3.19 g/kg, and 1.60~1.69 g/kg, respectively, with both C and N contents decreasing with increasing soil depth. Furthermore, the C and N contents in the Robinia pseudoacacia L.+ Prunus sibirica L. were significantly higher than those in other types up to a depth of 80 cm, while P content showed no significant differences among types or soil layers. Soil C∶N ratio were significantly lower in Robinia pseudoacacia L.+ Prunus sibirica L. within the 0—40 cm layer, with no significant differences observed among vegetation types from 40—100 cm. Soil C∶P and N∶P ratios were significantly influenced by vegetation type, showing the highest values in the mixed forest of Robinia pseudoacacia L.and Prunus sibirica L.; Soil C∶N of these vegetation types showed no significant differences among layers . Soil C∶P and N∶P ratios were decreased with soil depth. Soil carbon storage 0—100 cm varied between 5.98~38.21 t/hm² and had significant differences among these types, with all of them showed the order: Robinia pseudoacacia L.+ Prunus sibirica L.> Robinia pseudoacacia L.> Prunus sibirica L.>Hippophae rhamnoides L.>Prunus davidiana (Carrière) Franch.+ Caragana korshinskii Kom.>grassland. In addition, the mixed plantation of Robinia pseudoacacia L. and Prunus sibirica L. had significantly higher carbon storage than other vegetation types. [Conclusion] Tree and shrub lands in the southern Ningxia mountainous region have superior nutrient cycling patterns and carbon sequestration capabilities compared to grasslands, with the mixed planting model of Robinia pseudoacacia L.and Prunus sibirica L. being the most effective. Therefore, creating mixed plantations is an important approach to enhance soil carbon sequestration capacity.

Abstract:[Objective] To investigate the effects of different sand blending rates on the hydraulic properties and solute transport processes of moderately saline soils. [Methods] Four sand mixture ratios were established using an indoor soil column test: CK (0 sand mixing), B1 (10% sand mixing), B2 (15% sand mixing), and B3 (20% sand mixing), to investigate the solute transport characteristics of moderately saline soils under different sand mixing conditions and to perform model simulations. [Results] (1) In the range of 0~20%, sand mixing in moderately saline soil will obviously affect the change of soil moisture characteristic curve, and the larger the proportion of sand mixing, the closer the curve is to the Y-axis. Under any suction condition, the soil water content was ranked as CK>B1>B2>B3, and the larger the proportion of sand mixing, the more small pores in the soil, the reduction of small pores, and the weakening of soil water-holding properties. The saturated hydraulic conductivity of the soil increased with the increase of sand doping. (2) With the increase of sand doping, the solute penetration curve shifted significantly to the left, and the initial penetration time, complete penetration time, and total penetration time were reduced, and the total penetration time of B1, B2, and B3 treatments were reduced by 34.48%, 47.22%, and 69.71%, respectively, compared with that of CK. (3) Both the CED equation and the two-zone model can simulate the solute transport in soil under sand doping conditions well, but the fitting accuracy of the two-zone model is higher compared with the CDE equation. Analyses of the fitted parameters of the two-zone model showed that the soil pore flow rate, the water content ratio of the movable zone and the mass exchange coefficient gradually increased with the increase of sand doping, while the hydrodynamic dispersion coefficient and the dispersion degree showed a decreasing trend. [Conclusion] Therefore, sand blending in saline soils can effectively improve soil hydraulic properties, promote solute transport in the soil, and help alleviate the adverse effects of salinity on crop growth. The results of this study can provide reference for saline soil improvement and management work, and provide theoretical support and practical guidance for future research and practice.