Abstract: As common tree species,Indigofera amblyantha and Cassia bicapsularis have positive effects on slop stability and ecological restoration.To study their mechanism of slope protection,we investigated the influences of apparent morphology and roughness of roots on frictional strength of root-soil interface of 4-year age Indigofera amblyantha and Cassia bicapsularis.Results showed that:1)Grooves dominate the root skin of Indigofera amblyantha,and grids prevail on the root skin of Cassia bicapsularis.With the increase of root diameter,such apparent morphology grows more obvious.2)The roughness of root surface increases with the expansion of root diameter.When root diameter expands from 1 mm to 5 mm,the roughness of Indigofera amblyantha increases from 0.26 to 0.48,while that of Cassia bicapsularis from 0.24 to 0.66.3)Root with grid skin morphology has larger frictional strength on the root-soil interface,and the greater the roughness,the larger the frictional strength of root-soil interface.According to the micromorphology and quantified roughness as well as test verification,we established the relationship between the microstructure of root skin and the macroscopic friction and shear of root-soil interface.The research finding is of great significance for the study of the mechanical properties of slope protection by root system.

Key words: root, friction characteristic of root-soil interface, root surface roughness, microstructure, Indigofera amblyantha, Cassia bicapsularis