Abstract: Biological soil crusts (biocrusts) are the common cover in arid and semiarid areas. Together with plants, biocrusts affect runoff and flow velocity. However, few studies have focused on the effects of the co-covering of plant and biocrust (plant+biocrust) on the flow velocity, with a knowledge gap in the study of driving factors for slope erosion in arid and semiarid areas. In this study, simulated rainfall experiments were used to investigate the effects of biocrust and three types of biocrusts (more cyanobacteria less moss, more moss less cyanobacteria, and moss) on the flow velocity of revegetated grassland in the hilly Loess Plateau. The results showed that plant and plant+biocrust significantly reduced flow velocity, with that of plants and plant+biocrust being 70.7% and 83.1% lower than bare soil. The reduction benefits of plant and biocrust on flow velocity were 70.7% and 12.4%, respectively, when they were co-covered. Biocrust composition under plant cover affected flow velocity. The reduction benefits of more cyanobacteria less moss, more moss less cyanobacteria, and moss crust on flow velocity were 11.5%, 12.4%, and 19.4%, respectively. There was a significant negative correlation between flow velocity and moss coverage and a significant positive correlation between flow velocity and cyanobacteria coverage. The relationship between moss cove-rage (x) and flow velocity (y) was y=-2.081x+0.03 (R²=0.469). The moss coverage was a key factor affecting the flow velocity of co-covering of plant and biocrust slope with similar plant coverage (40%±10%). In conclusion, biocrusts under plant cover significantly slowed flow velocity, and the effect magnitude was related to its composition, implying that the role of biocrusts should be considered in understanding the mechanism underlying slope erosion in revegetated grassland.

Key words: biocrust composition, revegetated grassland, flow velocity, flow velocity reduction benefit