Background In recent years, with the trend of large-scale agricultural development, the intensity of development and utilization along riverbanks has increased continuously, resulting in varying degrees of damage to the vegetation buffer zones, and soil and water loss has become increasingly severe. The riparian vegetation buffer zone is an important component of riverbank ecosystems and plays a crucial role in soil consolidation and slope protection. However, the roles of different species in vegetation buffer zones along riverbanks in terms of soil and water conservation are still unclear.

Methods In this study, the riparian vegetation buffer zone in the Tongnan section of the Fujiang River Basin was selected as the research object. Through sample plot surveys, the species composition and types of dominant species were identified. The morphological characteristics and tensile strength of the plant roots were obtained through measurements of root mechanical and morphological traits. Indoor and field simulation experiments were conducted to determine the anti-scourability resistance and shear strength of root-soil composites for different dominant species.

Results 1) The main results are as follows: there are a total of 35 species belonging to 2 phyla, 3 classes, 16 orders, 19 families, and 30 genera of plants in the riparian buffer zone, mainly comprising angiosperms and ferns. The dominant species include Cynodon dactylon, Setaria viridis, Phragmites australis, Erigeron canadensis, and Melilotus officinalis. 2) When the root diameter is less than 0.2 mm, the tensile strength of C. dactylon roots is the highest, and when the diameter is larger than 0.2 mm, M. officinalis roots have the highest tensile strength. 3) The presence of plant root systems has a significant anti-scourability effect, with a time delay of 1–4 min for maximum scouring depth, a decrease in erosion depth of 9–38 mm, and a reduction in scouring amount of 20.17%–58.90%. The anti-scourability effect of C. dactylon is significantly better than that of S. viridis. The root system significantly enhances the shear strength of the soil, delaying the shear peak by 0.26–4.8 cm, increasing the shear peak by 4.76–11.37 kPa, and increasing energy consumption by 23.76%– 46.11%. P. australis has the best resistance to shear, followed by E. canadensis, and M. officinalis is the least resistant.

Conclusions Among the dominant species in the riparian vegetation buffer, the one with the best anti-scourability effect is C. dactylon, while the one with the best shear resistance is P. australis. Therefore, to balance the anti-scourability effect and shear resistance of plant roots, it is recommended to use a combination of C. dactylon and P. australis for shallow-rooted and deep-rooted planting, to enhance the water and soil conservation capacity of riverbanks.