[Effects of shrub-grass vegetation and biocrusts on soil and water loss and hydrodynamic characteristics of Loess Plateau slopes under rainstorm conditions].

During the initial stages of vegetation restoration on the Loess Plateau, shrub-grass vegetation effectively mitigates soil erosion caused by intense rainfall, while biological soil crusts (biocrust) and vegetation collectively can regulate runoff and sediment yield processes. However, their combined effects are usually overlooked. To quantify the impacts of shrub-grass vegetation and biocrust on runoff-sediment dynamics and to elucidate their synergistic effects on erosion mechanics, we conducted indoor artificial simulations of short-duration, high-intensity rainfall events, with nine treatments: bare soil (CK, no vegetation/biocrust); grassland; shrub; biocrust with 20% coverage; grassland+biocrust with 20% coverage; shrub+biocrust with 20% coverage; biocrust with 40% coverage; grassland + biocrust with 40% coverage; and shrub + biocrust with 40% coverage. The results showed that: 1) During the rainfall events, CK consistently exhibited the highest sediment volume, while the shrub, grass, and biocrust significantly reduced erosion. 2) Compared to the CK, shrub and grass reduced runoff by 21.9% and 18.2%, respectively, which promoted soil moisture infiltration. In contrast, biocrust with 20% and 40% coverage increased runoff by 9.5% and 17.4%, respectively, indicating that biocrusts inhibited infiltration. The positive effect of vegetation on soil infiltration surpassed the negative impact of biocrusts under vegetation+biocrust conditions. 3) The grassland+biocrust with 20% coverage treatment and all treatments with 40% biocrust generated subcritical flow, while other treatments were supercritical flow. All treatments showed lower average flow velocity and flow kinetic energy than CK, but exhibited higher flow shear stress and resistance coefficients. Compared to the CK, the grassland+biocrust with 40% coverage treatment demonstrated the highest runoff shear stress and resistance coefficient, with 164.5% and 213.8% increases, respectively, while the runoff kinetic energy was the lowest, decreasing by 91.9%. These findings suggested that maintaining appropriate biocrust coverage during the early stages of vegetation recovery could be helpful for enhancing soil conservation and ecosystem stability. Under the experimental conditions, the grassland+biocrust with 40% coverage treatment is optimal for soil erosion reduction.