Cracks in the mattic epipedon of alpine meadows are a key morphological indicator of ecosystem degradation. However, the accurate extraction of these minute and irregular crack features remains a significant challenge in complex natural environments characterized by vegetation cover, drastic fluctuations in light intensity, and soil texture interference. To address these challenges, a novel deep learning network, YOLO-AMSC, is proposed for the high-precision segmentation and morphological quantification of cracks in the mattic epipedon of alpine meadows under complex field environments. A Spatial to Depth Attention Fusion (SDAF-Block) module is proposed to preserve fine-grained spatial details of minute cracks without information loss and to reconstruct their broken topological continuity. Simultaneously, a Mixed Local Channel Attention (MLCA) mechanism is introduced to adaptively enhance crack textures while suppressing background noise. Furthermore, a hierarchical focused loss function, termed HFP-IoU (Hierarchical Focal-Penalty IoU), is designed to impose strict geometric constraints on the elongated crack boundaries via a non-monotonic focusing mechanism. The experimental results demonstrate that YOLO-AMSC achieves superior segmentation performance, improving mAP50 by 4.27%, 2.96%, 2.43%, 4.58%, 8.86%, 12.51%, 22.03%, 55.77%, and 52.19% compared with YOLOv5n-seg, YOLOv10n-seg, YOLO-hyper-seg, YOLOv12n-seg, SOLOv2, SparseInst, DeepCrack, CrackFormer-II, and CrackSegDiff, respectively. Using the high-fidelity segmentation masks from this model and a skeleton-based geometric constraint method for crack width estimation, the relative error relative to field measurements is less than 10%. Employing a system dynamics framework, this study quantitatively determines the topological width thresholds of 0.6 cm and 3.1 cm, which signify a sudden increase in connectivity and indicate an accelerated degradation process of alpine meadows. This method directly links pixel-level image analysis with regional early warning systems, delivering a cost-effective, non-destructive digital framework for dynamic ecological monitoring.

The formation and expansion of surface cracks during alpine meadow degradation are usually accompanied by the weakening of ecological functions, such as water conservation, nutrient retention, and biodiversity maintenance. As early-stage precursors of macroscopic cracks and a specific type of macropore, the formation and expansion of microcracks can reflect the structural deterioration of the mattic epipedon at the microscopic scale. This study aims to quantitatively characterize the morphological features of surface microcracks and pore structure dynamics across different degradation stages of alpine mattic epipedons, in order to elucidate the microstructural mechanisms underlying meadow degradation. This study investigated alpine mattic epipedons across four degradation stages. Using X-ray CT scanning, microcrack parameters, including microcrack number density, equivalent diameter, aspect ratio, and root distribution, were quantitatively analyzed in the surface layer of the mattic epipedon (0–6 cm). The results showed that, as alpine meadow degraded from the Normal State Meadow (NS) to the Eroded Mattic Epipedon State Meadow (ES), soil compaction degree increased from 719.15 kPa to 1265.00 kPa, whereas volume porosity decreased from 26.03

During the degradation process of alpine meadows, the vegetation-root-soil system has degraded synergistically, and the composition and structure of mattic epipedons have altered, resulting in gradual thickening accompanied by the emergence of cracks and a qualitative shift in the degradation state. Clarifying root-soil-crack interactions during this process remains challenging. In this study, root-soil properties and crack evolution were investigated using redundancy analysis (RDA), and root reinforcement effects were quantified through the Wu-Waldron model (WWM). The results revealed that degradation significantly affected soil structure, root architecture, and crack morphology (p < 0.05). Anthropogenic disturbances drove a compositional shift in plant communities from fine-rooted graminoids and sedges with high tensile strength to coarse-rooted forbs with lower tensile strength. This transition reduced the soil reinforcement capacity by about 44%, generating stress-weakened zones within the mattic epipedon that initiated surface cracking. RDA revealed root length density as the primary driver regulating crack propagation and morphological evolution. Furthermore, crack development exacerbates soil and water erosion, impedes vegetation and root growth, and further destabilizes the turf layer. Exacerbated by external environmental stresses, specifically wetting-drying and freeze-thaw cycles, crack expansion accelerates, triggering a self-reinforcing cycle of degradation. Crucially, we identified a critical threshold: once the fractal dimension of the crack network reached about 1.58, the alpine meadow ecosystem underwent irreversible degradation. This study elucidated the coupled interactions between root-soil properties and crack development under degraded conditions, offered diagnostic indicators for a more intuitive assessment of meadow degradation, and provided a theoretical basis for understanding the development, progression, and ecological regulation of mattic epipedon cracks in alpine meadow ecosystems.

The impact mechanism of vegetation on slope soil water infiltration and stability in the loess areas of the northeastern Qinghai-Tibet Plateau remains unclear. Understanding this mechanism is crucial for regional ecological restoration and shallow geological disaster prevention. This study investigated slopes covered by Caragana korshinskii Kom. by employing double-ring infiltration tests to explore the permeability characteristics and influencing factors of root-containing soils and to propose an appropriate infiltration model. Considering the synergistic effects of the canopy and roots, the hydrological response and stability of vegetation-covered slopes under rainfall infiltration conditions were evaluated through numerical simulation analysis. The results revealed that within the main root distribution layer (0-0.5 m), the initial and average infiltration rates and the permeability coefficient of the root-soil composite were significantly higher than those of bare land. Coarse roots with diameters of > 5 mm were the key contributors to enhancement of the infiltration capacity. The dry density, fine particle content, and initial water content of the soil around the roots were negatively correlated with the infiltration process. The Horton model effectively reproduced the infiltration process under the canopy and on bare land. The roots significantly accelerated the advance of the slope wetting front during rainfall infiltration, whereas the canopy delayed its onset and progression. The rainfall infiltration process on vegetation-covered slopes was divided into three stages: the equilibrium infiltration stage, optimal infiltration stage beneath the canopy, and secondary equilibrium stage. Vegetation enhances slope stability through coupling of the canopy and root, with an order of canopy-root mode > root mode > bare slope. Under heavy rainfall conditions, the direct contribution of canopy interception to slope stability is limited, and its primary role is to delay the occurrence of instability. During this period, the mechanical effect of roots becomes the dominant mechanism in slope protection.

The tensile mechanical properties of alpine meadow soils in the Yellow River Source Region (YRSR) are a key control on the stability of meandering riverbanks. To elucidate how freeze-thaw cycling and meadow degradation affect the tensile strength of riparian root-soil composites, we investigated meander bends with different degradation levels along the Lanmucuo River. We conducted laboratory uniaxial tensile tests on reconstituted root-soil specimens and complementary DEM simulations under three parameter sets: number of freeze-thaw cycles, root content, and root-species composition. We then analyzed the microscale mechanisms of freeze-thaw damage in rooted soils and the associated root-reinforcement processes. The results show that, the peak tensile strength decreases by 45% after seven freeze-thaw cycles. Specimens with 1% root content exhibit a 61.1% lower tensile strength than those with 4% root content. Reducing the proportion of sedge roots weakens the tensile strength of the root-soil composite. From one to seven freeze-thaw cycles, tensile and shear fracture contact fractions increase, with growth slowing after the fourth cycle. Increasing root content reduces both tensile and shear fracture contact fractions. Freeze-thaw reduced the peak root tension and surface contact force and increased the yield displacement of these forces. Lower sedge proportion and reduced root content led to smaller peak root tension and surface contact force and caused the yield displacement to occur earlier. Sensitivity analysis indicates that the soil effective modulus and tensile strength are the primary determinants of the composite elastic modulus and composite tensile strength, respectively, whereas the softening modulus is governed predominantly by root properties and root-soil interfacial contact parameters.

This study employed artificial simulated rainfall erosion experiments to investigate the response mechanisms of plateau pika mound patches to soil erosion and nutrient loss in the alpine meadow region of Henan County, Qinghai Province, China. The objectives were to elucidate the hydraulic erosion characteristics of pika mound patches, the patterns of soil nutrient loss during different vegetation recovery stages, and the influence of vegetation recovery on slope hydraulic erosion. The results showed that: (1) With increasing slope gradient, both the physical-mechanical properties and biological characteristics of soil in pika mound patches declined under the same recovery period. However, under identical slope gradients with varying recovery periods, soil loss volume initially increased and then decreased with rainfall duration, with the 15–20 min interval identified as the sensitive period for soil loss; soil sediment yield exhibited a sharp initial increase followed by a gradual decline, peaking between 20 and 25 min. (2) Nutrient loss rates followed the order: organic matter > available potassium > total potassium > alkali-hydrolyzable nitrogen > available phosphorus > total nitrogen > total phosphorus. Soil nutrient loss was most pronounced during the 2–3 year recovery period. Average flow velocity, Reynolds number, and Manning’s roughness coefficient were identified as the primary controlling factors influencing soil nutrient loss. (3) Correlation analysis revealed a significant negative relationship (P < 0.05) between the biotic characteristics of rodent mound patches and soil loss rates. Runoff width, average flow velocity, Reynolds number, and Manning’s roughness coefficient were all significant factors influencing soil nutrient loss (P < 0.05). (4) Structural equation modeling indicated that vegetation and soil properties significantly altered slope hydrodynamics, with vegetation characteristics in pika mound patches exerting indirect effects by influencing soil physical and mechanical properties. The study demonstrates that during vegetation recovery, pika mound patches in alpine regions enhance erosion suppression over time through improved soil and biological properties, thereby effectively reducing soil erosion risk.

The mound-making behavior of plateau zokors is one of the most important factors in remodeling meadow microtopography and causing soil erosion in the Yellow River source area of western China, but little is known about the effects of microtopography on particle size characteristics (PSC) of eroded sediments from the bare slopes of zokor mounds during different rainfall events. In this study, we analyzed the relationship of microtopographic features derived from laser point cloud data and PSC of eroded sediments at six simulated rainfall intensities (all lasting 60 min). The effects of microtopography on PSC of eroded sediments were studied via partial least squares regression (PLSR) and structural equation modeling (SEM). The results showed that: (1) 15–20 minutes from the beginning of rainfall was the sensitive period of soil loss from the slopes, and the function relationship between the rate of sediment and runoff and rainfall intensity can better predict the development trend of soil erosion; (2) Intense erosion occurred mainly in the upper half of the zokor mound, while deposition was mainly limited to its lower half. It is suggested that diminished plateau zokor activity intensity can effectively prevent and control soil erosion; (3) The PSC of eroded sediment is dominated by silt, followed by sand, with clay being the least abundant, and the eroded sediments with a particle size of 10–20 μm were sensitive and highly susceptible to rainfall erosion. This finding facilitates the understanding of the formation process of surface geomorphology and the mechanism of soil erosion; (4) The PLSR model indicates that microtopography has an extensive influence on eroded sediments during hydraulic erosion, and the SEM analysis results further confirm that the fractal dimension was the best parameter to represent the PSC of eroded sediments, whereas surface cutting degree was the dominant factor controlling the PSC of eroded sediments. These findings are crucial for predicting soil erosion in the Yellow River source area and provide a new perspective for understanding soil erosion mechanisms in alpine meadow ecosystems.

Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration. Quantitative research remains insufficient regarding changes in the mechanical properties of degraded meadow soils and the mechanical thresholds for cracking initiation. This study explored the relationships between surface cracking and the physical properties, tensile strength, and matrix suction of root-soil composites in alpine meadow sites with different stages of degradation (undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)) under different water gradients (high water content (HWC), medium water content (MWC), and low water content (LWC)) corresponding to different drying durations at a constant temperature of 40.0°C. The Huangcheng Mongolian Township in Menyuan Hui Autonomous County, Qinghai Province, China was chosen as the study area. The results indicated that as the degradation degree of alpine meadow intensified, both water content of root-soil composite and the fine grain content of soil decreased. In contrast, the root-soil mass ratio and root area ratio initially increased and then decreased with progressive degradation. Under a consistent water content, the tensile strength of root-soil composite followed a pattern of MD>HD>LD>UD. The peak displacement of tensile strength also decreased as the degradation degree of alpine meadow increased. Both the tensile strength and matrix suction of root-soil composite increased as root-soil water content decreased. A root-soil water content of 30.00

The mound-building behavior of plateau pika is one of the important factors leading to meadow degradation and soil erosion in the Yellow River source area of Western China, but little is known about the influencing mechanism of microtopography on erosion hydrodynamic characteristics of bare slopes of pika mounds. In this study, we analyzed microtopography and erosion hydrodynamic characteristics on bare slopes of pika mounds under subrainfall conditions through simulation of rainfall events at six intensities (all lasting 60 min), and revealed the influencing mechanism of slope microtopographic changes on erosion hydrodynamics by using redundancy analysis (RDA) and structural equation modeling (SEM). The results showed that the maximum average erosion depth was 4.159 cm, and the maximum erosion areas accounted for 93.40 % of the total area of runoff plots; intense erosion took place mainly in the upper half of the pika mounds, while deposition was mainly limited to the lower half of the pika mounds. Surface flow velocity, flow regime parameters, and erosion power parameters all showed an increasing trend with rainfall intensity (P < 0.05), while the resistance parameters showed a decreasing trend with rainfall intensity (P < 0.05); all slope flows were laminar (Re < 500), but transitioned from slow flows to rapid flows at a higher rainfall intensity. The RDA results showed that surface cutting degree was the key factor influencing surface runoff volume and sediment yield and hydrodynamic parameters, and that the Reynolds number could be the best hydrodynamic parameter to characterize runoff volume and sediment yield. SEM analysis showed that microtopography influenced water erosion either directly (with a path coefficient of 0.856) or indirectly through hydrodynamic characteristics (path coefficient = 0.742). This research showed that microtopography of the bare slopes had a significant effect on water erosion, and was linked to hydrodynamic characteristics to build up a highly complex dynamic exchange process.

Soil erosion and shallow landslides in the upper reaches of the Yellow River, China, are increasing due to extreme climate events and human disturbances. The biomechanical properties of vegetation roots play an important role in soil stabilization and fixation, as they resist soil erosion and shallow landslides in this area. However, the biomechanical properties of the roots of dominant herbs and their influencing factors in this area remain poorly understood. Therefore, we selected two dominant herbs in this area, Stipa aliena Keng and Poa crymophila Keng, and carried out a series of uniaxial tensile tests on the roots of the two herbs under different treatments. Meanwhile, the effects of root diameter, plant species, gauge length, root water content, and loading rate on the biomechanical properties of the two herbs’ roots were analyzed. The results showed that root diameter was the most significant factor affecting the root biomechanical properties (P<0.010), and root tensile force displayed a positive power law relationship with root diameter, whereas root tensile strength and Young’s modulus followed negative power law correlations with root diameter, and fracture strain increased linearly with root diameter. Root tensile force, tensile strength, and fracture strain of S. aliena were significantly greater than those of P. crymophila (P<0.001), which was mainly due to the higher lignin content and lignin:cellulose ratio of S. aliena roots. During uniaxial tensile process, hydrated roots exhibited elastic-plastic-brittle behavior, whereas dried roots exhibited elastic-brittle behavior. Root fracture strain of the two herbs was significantly lower under 100 mm gauge length than under 50 mm gauge length (P<0.001), and the Young’s modulus was significantly greater (P<0.050). Tensile strength and fracture strain of hydrated roots of the two herbs were significantly greater than those of dried roots (P<0.050), whereas the Young’s modulus was significantly lower (P<0.001). Root tensile force, tensile strength, and fracture strain of S. aliena were significantly greater under 20 mm/min loading rate than under 200 mm/min loading rate (P<0.050), whereas loading rate had no significant effect on the root biomechanical properties of P. crymophila (P>0.050). Fibrous roots of the two herbs were well developed, with relatively high tensile strengths and Young’s moduli of 78.498 and 837.901 MPa for S. aliena, and 67.541 and 901.184 MPa for P. crymophila, respectively. The two herbs can stabilize soil and prevent soil erosion and can be used as pioneer species for ecological restoration in the upper reaches of the Yellow River. These results provide a theoretical basis for soil erosion and shallow landslide control in the giant landslide area of the upper reaches of the Yellow River.

Soil moisture plays an important role in maintaining ecosystem stability and sustainable development, especially for the upper reaches of the Yellow River region. Therefore, accurately and conveniently monitoring soil moisture has become the focus of scholars. This study combines three machine learning algorithms: random forest (RF), support vector machine (SVM), and back propagation neural network (BPNN)—with the traditional monitoring of soil moisture using remote sensing indices to construct a more accurate soil moisture inversion model. To enhance the accuracy of the soil moisture inversion model, 27 environmental variables were screened and grouped, including vegetation index, salinity index, and surface temperature, to determine the optimal combination of variables. The results show that screening the optimal independent variables in the Xijitan landslide distribution area lowered the root mean square error (RMSE) of the RF model by 16.95%. Of the constructed models, the combined model shows the best applicability, with the highest R2 of 0.916 and the lowest RMSE of 0.877% with the test dataset; the further research shows that the BPNN model achieved higher overall accuracy than the other two individual models, with the test set R2 being 0.809 and the RMSE 0.875%. The results of this study can provide a theoretical reference for the effective use of Landsat satellite data to monitor the spatial and temporal distribution of and change in soil water content on the two sides of the upper Yellow River basin under vegetation cover.

Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development.Crack characterization indices are crucial for the quantitative characterization of complex cracks,serving as vital factors in assessing the degree of cracking and the development morphology.So far,research on evaluating the degree of grassland degradation through crack characterization indices is rare,especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce.Therefore,based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau,we selected the alpine meadow in the Huangcheng Mongolian Township,Menyuan Hui Autonomous County,Qinghai Province,China as the study area,used unmanned aerial vehicle(UAV)sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation(light,medium,and heavy degradation),and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length,length density,branch angle,and burrow(rat hole)distribution density and combining them with in situ crack width and depth measurements.Finally,the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis.The results revealed that with the increase of degradation,the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly,the vegetation coverage reduced,and the root system aggregated in the surface layer of alpine meadow.As the degree of degradation increased,the fracture morphology developed from"linear"to"dendritic",and eventually to a complex and irregular"polygonal"pattern.The crack length,width,depth,and length density were identified as the crack characterization indices via analysis of variance.The results of grey relation analysis also revealed that the crack length,width,depth,and length density were all highly correlated with root length density,and as the degradation of alpine meadows intensified,the underground biomass increased dramatically,forming a dense layer of grass felt,which has a significant impact on the formation and expansion of cracks.

Characteristics of root pullout resistance determine the capacity to withstand uprooting and the slope protection ability of plants. However, mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau, China remains unclear. In this study, a common taproot-type shrub, Caragana korshinskii Kom., in northeastern Qinghai-Xizang Plateau was selected as the research material. Mechanism of root-soil interaction of vertical root of C. korshinskii was investigated via a combination of a single-root pullout test and numerical simulation analysis. The results indicated that, when pulling vertically, axial force of the roots decreased with an increase in buried depth, whereas shear stress at root-soil interface initially increased and then decreased as burial depths increased. At the same buried depth, both axial force and shear stress of the roots increased with the increase in pullout force. Shear stress and plastic zone of the soil surrounding the root were symmetrically distributed along the root system. Plastic zone was located close to the surface and was caused primarily by tensile failure. In nonvertical pulling, symmetry of shear stress and plastic zone of the soil surrounding the root was disrupted. We observed larger shear stress and plastic zones on the side facing the direction of root deflection. Plastic zone included both shear and tensile failure. Axial force of the root system near the surface decreased as deflection angle of the pullout force increased. When different rainfall infiltration depths had the same vertical pulling force, root axial force decreased with the increase of rainfall infiltration depth and total root displacement increased. During rainfall infiltration, shear stress and plastic zone of the soil surrounding the root were prone to propagating deeper into the soil. These findings provide a foundation for further investigation of soil reinforcement and slope protection mechanisms of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau and similar areas.

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai–Tibet Plateau, China. However, there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods. We selected dump areas of the Delni Copper Mine in Qinghai Province, China to study the relationship between the shear strength and the peak displacement of the root-soil composite on the slope during the recovery period, and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root-soil composite via in situ direct shear tests. The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period. The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship. There is no significant function relationship between the peak displacement and the recovery period. Significant positive correlations (P < 0.05) exists between the shear strength of the root-soil composite and the root biomass density, root volume density, and root area ratio, and they show significant linear correlations (P < 0.05). There are no significant correlations (P > 0.05) between the shear strength of the root-soil composite and the root length density, and the root volume ratio of the coarse roots to the fine roots. A significant negative linear correlation (P < 0.05) exists between the peak displacement of the rooted soil and the coarse-grain content, but no significant correlations (P > 0.05) with the root traits, other soil physical property indices (the moisture content and dry density of the soil), and slope gradient. The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.

In order to study the infiltration characteristics of grassland soil in the super large scale landslides distribution area in the upper reaches of the Yellow River, this study selected the Xiazangtan super large scale distribution area in Jianzha County as the study area. Through experiments and numerical simulations, plant roots characteristics, soil physical properties and infiltration characteristics of naturally grazed grassland and enclosed grassland with different slope directions were compared and analyzed, and the influence of rainfall on seepage field and stability of the two grassland slopes were discussed. The results show that the highest soil moisture infiltration capacity (FIR) is found on the shady slope of the enclosed grassland (2.25), followed by the sunny slope of the enclosed grassland (1.23) and the shady slope of the naturally grazed grassland (-0.87). Correlation analysis show that soil water content, root dry weight density, total soil porosity, number of forks and root length are positively correlated with infiltration rate (P < 0.05), whereas soil dry density is negatively correlated with infiltration rate (P < 0.05). The results of stepwise regression analyses show that soil water content, total soil porosity, root length and number of forks are the main factors affecting soil infiltration capacity. And the ability of roots to increase soil infiltration by improving soil properties is higher than the effect of roots itself. After 60 min of simulated rainfall, the safety factors of the shady slopes of naturally grazed grassland and enclosed grassland are reduced by 29.56% and 19.63%, respectively, comparing to those before rainfall. Therefore, in this study, the roots play a crucial role in regulating soil infiltration and enhance slope stability by increasing soil water content, soil total porosity and shear strength while decreasing soil dry density. The results of this study provide theoretical evidence and practical guidance for the effective prevention and control of secondary geological disasters such as soil erosion and shallow landslide on the slope of river banks in the study area by using plant ecological measures.

In order to study the root–soil composite system shear characteristics under the action of freeze–thaw cycles in the permafrost regions along the Qinghai–Tibet Highway (QTH) from the Beiluhe–Tuotuohe (B-T) section, the slopes in the permafrost regions along the QTH from the B-T section were selected as the object of the study. The direct shear test of root–soil composite systems under different amounts of freeze–thaw (F-T) cycles and gray correlations were used to analyze the correlation between the number of F-T cycles, water content, root content, and the soil shear strength index. The results show that the cohesion of the soil in the area after F-T cycles exhibits a significant stepwise decrease with an increase in F-T cycles, which can be divided into three stages: the instantaneous stage (a decrease of 46.73–56.42%), the gradual stage (a decrease of 14.80–25.55%), and the stabilization stage (a decrease of 0.61–2.99%). The internal friction angle did not exhibit a regular change. The root–soil composite system showed significant enhancement of soil cohesion compared with soil without roots, with a root content of 0.03 g/cm3 having the most significant effect on soil cohesion (increasing amplitude 65.20–16.82%). With an increase in the number of the F-T cycles, while the water content is greater than 15.0%, the greater the water content of the soil, the smaller its cohesion becomes. Through gray correlation analysis, it was found that the correlation between the number of F-T cycles, water content, root content, and soil cohesion after F-T cycles were 0.63, 0.72, and 0.66, respectively, indicating that water content had the most significant impact on soil cohesion after F-T cycles. The results of this study provide theoretical support for further understanding the variation law of the shear strength of root–soil composite systems in permafrost regions under F-T cycles and the influencing factors of plant roots to enhance soil shear strength under F-T cycles, as well as for the scientific and effective prevention and control of retrogressive thaw slump in the study area, the QTH stretches across the region.

Numerous rodent mounds are found in areas with rodent activity in alpine grasslands in the Yellow Riv-er source zone,and soil wind erosion easily occurs owing to the dry and windy climate.The present study investi-gated the characteristics and trends of soil wind erosion in rodent mounds using plateau pika(Ochotona curzoni-ae)and plateau zokor(Eospalax baileyi)mounds in 14 test areas at different altitudes and with different vegeta-tion coverage in the Yellow River source basin.Field-simulated wind erosion was used to determine the trends of soil loss and nutrient loss in rodent mounds in different regions under different wind speeds.The results showed a significant difference in the amount of soil loss from wind erosion between the different regions(P<0.05).When the wind speed was low,there was no significant difference in soil loss between the two types of rodent mounds.When the wind speed was increased to 12 m·s-1,the soil loss in the plateau pika mound was greater than that in the plateau zokor mound(P<0.05).When the wind speed increased from 3 to 12 m·s-1,the average increase in soil loss in the two types of mounds was 238.16%and 146.31%,respectively.(2)The wind erosion rate of the mound soil in each test area generally showed a decreasing trend with decreasing wind speed.Vegetation cover-age was a significant factor affecting the mound soil loss at low wind speeds and was related to altitude.(3)With an increase in grassland degradation levels,the soil total nitrogen content,available nitrogen,available potassi-um,and organic matter content decreased significantly,whereas total phosphorus,total potassium,and available phosphorus showed an upward trend.This study shows that the difference in soil wind erosion in different re-gions of the Yellow River source zone is closely associated with soil moisture content,particle size,and wind speed.

河岸带土体的抗剪性能直接影响河岸稳定性,冻融作用对高寒草甸土体的结构和抗剪力学特性的影响直接关系到黄河源区河岸的崩退频率和横向迁移.为探究冻融作用下,黄河源区曲流河岸带含根土体抗剪强度指标的变化规律及其产生机制,通过室内重塑土冻融直剪试验,开展不同含根量和冻融循环次数对土体抗剪强度指标的影响研究.结果表明:(1)植物根系能显著增强土体黏聚力,且随根系含量增加,黏聚力增幅可达2.7%～77.9%;内摩擦角随含根量变化不明显;(2)冻融循环具有削弱土体黏聚力的作用,尤其冻融循环初期.3次冻融循环条件下,黏聚力下降最大,下降幅度达19.0%;随着冻融循环次数增加,其变化基本趋于稳定,内摩擦角则随冻融循环次数增加呈现略微增大的趋势;冻融作用对含根土体抗剪强度指标的影响较素土小,在同等冻融次数条件下,含根试样黏聚力降低幅度较素土试样小.(3)草甸植物根系能够在一定程度阻隔土体温差变化,减缓土体黏聚力下降幅度,且随含根量增加而增强,含根量达到11%时,其对土体黏聚力的削弱作用较素土小4.2%～27.7%.因此,黄河源区河岸带应加强保护滨河草甸植被,最大限度发挥根系增强河岸稳定性作用,保护河流生态.

Shrub species Caragana korshinskii Kom. dominates slope protection and soil and water conservation in the loess area of the northeastern Qinghai–Tibet Plateau. However, the root anchoring mechanism and the effects of soil consolidation and slope protection of this shrub species remain unclear. This study aimed to elucidate the anchoring mechanism of roots of the C. korshinskii roots and establish a calculation model to evaluate their contribution to the stability of shallow loess slopes. C. korshinskii plants with an 11-year growth period were selected as the study subject. The anchoring force of C. korshinskii roots was determined through in-situ excavation tests, in-situ root pullout tests, and theoretical analysis, along with their impact on the stability of shallow loess soil slopes. The results showed that, due to the absence of a “bolt head” structure on the root surface, it was reasonable to consider the anchoring force provided by the roots as the minimum value between the maximum pullout resistance of the roots below the sliding surface and the anchoring reaction force of the roots above the sliding surface, based on the geometric characteristics of the sliding surface. When the roots of an 11-year-old C. korshinskii roots were anchored on different sliding blocks of a shallow landslide with a maximum thickness of 2 meters, the stability coefficient of the potential sliding surface increased by 0.020% to 0.408%. When the roots of a single plant were anchored in the middle and upper parts of the potential sliding surface, the stability coefficient of the potential sliding surface was relatively higher than when the plant roots were anchored at the top and bottom positions. Moreover, when four C. korshinskii roots were anchored to the shallow landslide with a row spacing of two sliding blocks (approximately 3 m), the stability coefficient of the potential sliding surface increased by 1.035% to 1.111%, which was significantly higher than when a single C. korshinskii root was anchored (P<0.05, ANOVA). The anchorage effect of the root systems could enhance the stability of shallow soil on loess slopes under rainfall infiltration conditions, but the effectiveness was limited.

[Objective] The effects of different factors on the shear strength index and shear strength of the root-soil interface were analyzed, in order to provide an understanding of the mechanism of shrub root soil fixation and slope protection in the loess region of the Northeastern Tibetan Plateau. [Methods] The dominant shrub (Caragana korshinskii) for this region was selected as the study object, and the effects of the dry density, moisture content, and salt content of soil, and of root diameter on the shear characteristics of the root-soil interface and their mechanisms were analyzed and discussed using the direct shear test (i. e., one factor was varied at a time) for root diameters of (2.20±1.00—32.00±1.80) mm and moisture contents, dry densities, and salt contents of the soil of 6.00%—22.00%, 1.20—1.60 g/cm3, and 0.59%—2.50% respectively. [Results] Root diameter had no significant effect on the shear strength indexes and shear strength of the root-soil interface (p>0.05) when other influencing factors were held constant. As soil moisture content increased from 6.00% to 22.00%, the root-soil interface cohesion initially increased and then decreased, reaching a maximum value of 6.74 kPa at a soil moisture content of 14.00%. The root-soil interface friction angle decreased linearly from 21.40° to 15.75°. The shear strength of the root-soil interface decreased linearly. As the soil dry density increased from 1.20 g/cm3 to 1.60 g/cm3, the cohesion of the root-soil interface increased exponentially from 5.70 kPa to 6.85 kPa, and the friction angle increased linearly from 20.67° to 21.67°. The shear strength of the root-soil interface increased linearly. As the soil salt content increased from 0.59% to 2.50%, the root-soil interface cohesion increased linearly from 6.71 kPa to 7.31 kPa, and the shear strength increased linearly. However, there was no significant change in the root-soil interface friction angle (p>0.05). The gray correlation analysis of these results showed that dry density had the greatest influence on the cohesion, the friction angle, and the shear strength of the root-soil interface. [Conclusion] The dry density, moisture content, and salt content of soil can all affect the shear characteristics of the root-soil interface, however, the degree of influence is different. The influence of rainfall infiltration on the shear characteristics of the root-soil interface should be fully considered when evaluating the protective effect of plant roots on the shallow soil of loess slopes.