Root traits and soil detachment in response to variable slope gradients in a representative purple-soil sloping grassland

Plant roots interact closely with soils and significantly affect soil erosion, which can be reflected in various root traits. Slope gradient is a topographic factor that considerably affects the interactions between root traits and soil erosion. However, little is known about the relationships between root traits and soil erosion, which are affected by slope gradient. This study investigated the responses of root traits and soil detachment to variable slope gradients in a representative purple-soil sloping grassland. Topsoil samples with vetiver (Chrysopogon zizanioides L.) roots (VT) and without roots (CK) were collected at three gradients (20°, 30°, and 40°) to determine the soil detachment capacity, the rill erodibility and critical shear stress. The root mass and morphology of the VT were also measured. The results showed that root mass density and root morphological traits related to the total roots (irrespective of root diameter) and roots with diameter ≤ 1.0 mm decreased markedly from 20° to 30°. The proportions of root morphology with diameter > 1.0 mm increased as slope gradients increased, suggesting that steep slopes could promote coarse roots. The soil detachment capacity was 34.1–49.6 % lower in VT than in CK under studied slope gradients, whereas these reductions did not differ with slope gradients. Lower rill erodibility and higher critical shear stress were found in VT under each slope than in CK, highlighting the role of roots in enhancing soil erosion resistance. Our results contribute to understanding the mechanisms by which roots on control soil water erosion in complicated, changing environments.