Introduction:Riparian vegetation plays a crucial role in soil conservation and riverbank reinforcement.The Three Gorges hydrologic project has significantly changed the pattern of water-level fluctuation and riparian environment,which significantly influenced plant community development and its effect on soil conservation and riverbank protection.Cynodon dactylon,a perennial grass with developed root system and creeping stems,has become a dominant riparian species in the Three Gorges area after the completion of the dam.We aimed to characterize how the soil-root system under the C.dactylon community responded to environmental changes and effects of the soil-root system on shallow soil conservation and riverbank reinforcement through field investigation and laboratory test.Methods:We conducted a field survey and experimental research.Quadrates of a natural C.dactylon community were set up on a riverbank along an altitude gradient.Plants were sampled randomly for the measurements of spatial structure and tensile strength of roots.Soil erosion resistance,soil scour resistance,and shear strength of sampled soil-root systems and control soil were tested in the laboratory.Results:Roots of the C.dactylon community significantly increased soil erosion resistance,soil scour resistance,and shear strength,enhancing the stability of shallow soil and riverbank.Due to water-level fluctuation,C.dactylon at lower altitudes was subjected to less time exposed to air.As a result,the soil-root systems at lower altitudes were characterized by reduced biomass with reduced capacity for soil reinforcement as measured through erosion resistance,soil scour resistance,and shear strength.The correlation analysis indicated that root biomass had a significant positive linear correlation with the enhancement of erosion resistance and scour resistance,and shear strength,respectively.Conclusions:Roots of the C.dactylon community effectively enhanced the stability of riparian shallow soil and riverbank.The fluctuation in water level caused the di
