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Failure of collapsing walls is an important process affecting the development of Benggang and is closely related to the soil shear strength. Plant roots can increase the soil shear strength. However, the effects and mechanisms of root reinforcement on the soil shear strength of collapsing walls remain unclear. To explore the shear strength characteristics of collapsing walls and their influencing factors under different vegetation conditions, Pennisetum sinese, Dicranopteris dichotoma, Odontosoria chinensis, and Neyraudia reynaudiana were adopted as experimental objects in the Benggang district of Anxi County, Southeast China. We measured the root characteristics and in situ shear strength of root–soil complexes by dividing soil with the four vegetation conditions into five soil layers: 0–5 cm, 5–10 cm, 10–15 cm, 15–20 cm, and 20–25 cm. The average shear strength of the root–soil complexes of the various plants ranked as follows: Pennisetum sinese (30.95 kPa) > Odontosoria chinensis (28.08 kPa) > Dicranopteris dichotoma (21.24 kPa) > Neyraudia reynaudiana (14.99 kPa) > bare soil (11.93 kPa). The enhancement effect of the root system on the soil shear strength was mainly manifested in the 0–5 cm soil surface layer. The soil shear strength attained an extremely significant positive correlation with the root length density, root surface area density, root volume density, root biomass density, for root diameters (L) less than or equal to 0.5 mm and between 0.5 and 1 mm, the soil shear strength could be simulated by using root volume density. The shear strength of undisturbed root–soil complexes measured with a 14.10 pocket vane tester was higher than the value obtained with the Wu–Waldron model (WWM). The correction coefficient k′ varied between 0.20 and 20.25, mostly exceeding 1, and the average correction coefficient k′ value was 4.94. The average correction coefficient determined in this test can be considered to modify the WWM model when conducting experiments under similar conditions. [ABSTRACT FROM AUTHOR]

• Vegetation restoration has improved the soil multifunctionality in eroded areas. • Vegetation restoration has increased the abundance and diversity of carbon-fixing functional bacteria. • Vegetation restoration has enhanced the network complexity of carbon-fixing functional bacteria. • The changes in carbon-fixing functional bacteria are closely related to the changes in soil multifunctionality. Carbon-fixing bacteria are a key functional group in soil carbon fixation processes, but their relationship with soil multifunctionality during vegetation restoration in eroded areas remains unclear. This hinders our ability to assess the true impact of vegetation restoration on soil ecosystem services. Therefore, we studied the impacts of three vegetation communities (tree-shrub, tree-grass, and tree-shrub-grass) in the same small watershed in a severely eroded area in southern China on the community of carbon-fixing bacteria in the soil. Compared to eroded areas, vegetation restoration sites had more complex networks of carbon-fixing bacteria, more carbon-fixing bacterial taxa, and more associations among these bacteria. Particularly, in the tree-shrub communities, the Chao1 index, Shannon index, node number, and edge number increased significantly by 291.29%, 49.65%, 364.58%, and 530.89%, respectively. The vegetation community pattern shifted the dominant carbon-fixing bacteria in the eroded areas from Rhodovastum to Nocardia. In the tree-shrub, tree-grass, and tree-shrub-grass patterns, the relative abundance of Rhodovastum decreased by 90.11%, 96.76%, and 95.37%, respectively, compared to that in the control group (CK). This indicates that vegetation community patterns have the potential to shift the dominant carbon-fixing bacteria from strict autotrophs to facultative autotrophs. The changes in the characteristics of the carbon-fixing bacterial community are closely related to the changes in soil multifunctionality caused by vegetation restoration. These results demonstrate that vegetation communities have a significant positive impact on the soil carbon fixation capacity. [ABSTRACT FROM AUTHOR]

The impact of vegetation restoration on soil structure, nutrients, and microorganisms in eroded areas has been extensively studied, but the effect of vegetation restoration on carbon-sequestering bacterial communities and their associated carbon fixation capacity remains largely unknown. In this study, we focused on the 0–20 cm soil layer in eroded and vegetation restoration sites in areas of southern China that have been severely affected by soil erosion and utilized 13C stable isotope labeling and high-throughput sequencing technologies to investigate the influence of vegetation restoration on carbon-sequestering bacterial communities and their carbon sequestration potential. Compared with eroded areas, vegetation restoration areas presented greater soil nutrient contents and greater diversity of bacteria with carbon sequestration functions. Vegetation restoration also altered the composition of carbon-sequestering bacterial communities by increasing the soil alkali-hydrolyzable nitrogen content, with the dominant carbon-sequestering bacteria shifting from Nocardia to Bradyrhizobium. However, the microbial carbon sequestration rate in soil erosion areas significantly increased by 2.15 times compared with that in vegetation restoration areas. Among the factors considered, pH (68.90 %, P = 0.000) was identified as the primary explanatory factor regulating changes in the microbial carbon sequestration rate. Our results are important for revealing the role of vegetation restoration in the global carbon cycle and elucidating the role of microorganisms in the soil carbon cycle. [ABSTRACT FROM AUTHOR]

• The vegetation restoration model added microbial abundance and diversity in soil erosion areas. • The increase of soil alkali-hydrolyzed nitrogen by vegetation restoration was the main explanation factor for the increase of bacterial diversity. • The increase of soil organic matter by vegetation restoration was the main explanation factor for the increase of fungal diversity. • The arbor-shrub -grassland model has the most obvious improvement on the stability of soil ecosystem. Investigating the effects of diverse artificial vegetation restoration methods on soil microbial communities is important for understanding soil health and achieving sustainable utilization of vegetation resources. In this study, the surface soil samples (0–10 cm) of three artificial vegetation restoration modes were selected as the research object which included the fenced forest, the arbor-shrub-grassland, and the chestnut forest in the soil and water loss area of South China. Three artificial vegetation restoration modes have significantly increased both the abundance and diversity of bacteria and fungi in areas affected by soil erosion, thus contributing to the stabilization of the ecosystem. Specifically, the arbor-shrub-grassland mode demonstrated the most significant improvements. Soil alkali nitrogen (71.10%, P = 0.000) and organic matter content (63.30%, P = 0.001) emerged as the primary factors driving this increase in bacterial and fungal diversity. After restoration, the composition of soil bacterial and fungal communities in soil erosion areas has undergone significant changes. However, it was observed that only the arbor-shrub-grassland mode could induce a shift in dominant bacterial species from Chloroflexi to Acidobacteria. Variations in soil bacterial and fungal community compositions across different modes were attributed to differences in soluble organic carbon (65.80%, P = 0.002) and soil bulk density (49.00%, P = 0.010). In conclusion, the increased fungal abundance and the bacterial shift observed in the arbor-shrub-grassland mode underscore its superior effectiveness in rehabilitating degraded soils, compared to both the fenced forest and the chestnut forest modes. [ABSTRACT FROM AUTHOR]

• A typical and common herbaceous plant of Neyraudia reynaudiana roots was selected as the research objective. • The effect of both moisture content and root density to root-soil complex are discussed. • Roots could enhance the soil shear strength mainly reflected in the increase of cohesive force. • Moisture content was introduced into the shear strength model of root-soil complex. The collapse of collapsing walls is a key process during the Benggang development in southeast China and is closely related to the soil shear strength. Plant root reinforcement can effectively improve the soil shear strength. However, there are few studies on the effect of roots on the soil shear strength of collapsing walls. To explore the influence of roots on the soil shear strength of collapsing walls, the roots of Neyraudia reynaudiana was selected as the research object. This paper studies the tensile properties of the roots through root tensile tests and performs a direct shear test to study the influence of the roots on the soil shear strength by setting different mass moisture contents (15%∼30%) and root weight densities (0 ∼ 1.25 g 100 cm−3). Root tensile force is positively correlated with root diameter by a power function, while tensile strength is negatively correlated with diameter by a power function. Roots could increase the soil shear strength, and which was mainly reflected in cohesive force. The shear strength and cohesive force increase first then decrease with the increasing root density, while root density has no effect on the internal friction. The shear strength, cohesive force and internal friction of root-soil complex all decreased with increasing moisture content. The WWM (Wu and Waldron model) greatly overestimated the cohesion of herbaceous roots, and a new prediction model of the shear strength of root-soil composites was obtained by revising the WWM model by introducing the moisture content and root density (NSE = 0.94). In conclusion, Neyraudia reynaudiana roots could improve the soil shear strength, whereas the strengthening effect decreased under the condition of high moisture content. The results provide a basis for the selection and allocation of vegetation restoration measures in Benggang erosion in southern China. [ABSTRACT FROM AUTHOR]

• Erosive responses of near soil surface factors were investigated in alluvial fans. • Root physical binding was the most effective at reducing soil detachment. • A deep-rooted plant better controlled soil detachment than a shallow-rooted plant. • Vegetation recovery effectively promoted soil resistance to erosion. Soil detachment processes are greatly impacted by vegetation recovery. However, the understanding of these relationships on bengggang alluvial fans in southeast China is limited. In this research, the impacts of near soil surface factors (litter stems, biological crusts, and roots) on soil detachment is quantitated by overland flow with two introduced grass species (Paspalum mandiocanum and Pennisetum giganteum) in the alluvial fans. Flow scouring was performed on soil samples obtained from two grasslands under nine forms of shear stress ranging from 2.70 to 10.51 Pa. Paspalum mandiocanum and Pennisetum giganteum significantly reduced the soil detachment capacity of alluvial fans by 94% and 98%, respectively. The roots of the two kinds of grass were most effective in reducing soil detachment (48% and 63%), the situation of >80% was caused by root binding; besides, the contribution of biological crusts (37% and 20%) was higher than that of litter-stems (9% and 15%). Compared with bare land, roots and biological crusts under Paspalum mandiocanum and Pennisetum giganteum decreased rill erodibility by 43% and 40%, 60% and 20%, respectively; meanwhile, they increased the critical shear stress by 0.92- to 3.02-fold, 1.15- to 3.34-fold, respectively. Roots of the two plants increased soil resistance more than the biological crusts mainly by root binding. Overall, Pennisetum giganteum (a deep roots plant) showed a slightly better performance in controlling soil detachment than Paspalum mandiocanum (a shallow roots plant); among them, the roles of roots and litter-stems of Pennisetum giganteum were greater than those of Paspalum mandiocanum while the role of biological crusts of Paspalum mandiocanum was greater than that of Pennisetum giganteum. These findings highlight the significance of litter-stems, biological crusts and roots in controlling soil erosion and are helpful for selecting suitable grasses for vegetation recovery in alluvial fans of benggang. [ABSTRACT FROM AUTHOR]