Response of plant community structure and soil water conservation function to forbidden grazing and enclosure in alpine steppe of the Qinghai Lake

[Objective] This study aims to explore the impact of grazing enclosure on plant community structure and soil water conservation function in alpine steppe in the Qinghai Lake region, and to evaluate the effects of grazing enclosure on the restoration of the degraded grassland in Qinghai Lake. [Methods] By setting up free grazing and different years of enclosure in the alpine grassland on the north bank of the Qinghai Lake, we analyzed the effects of enclosure measures on plant species, biomass, functional groups, soil bulk density, water holding capacity, porosity, and other indicators. [Results] (1) With the increasing of enclosure time, the number of species in the alpine steppe was decreased, the vegetation cover, above-ground biomass, and below-ground biomass were first increased and then decreased. The percentage of grasses in the community was gradually increased. (2) The effects of grazing exclusion on soil moisture characteristics of alpine steppe were mainly concentrated in the 0-20 cm depth. With the increase of grazing exclusion time, soil bulk density at 0-20 cm was decreased gradually, soil saturated water holding capacity, capillary water holding capacity, field water holding capacity, and total porosity at 0-10 cm was first increased and then stabilized. (3) Soil bulk density was the most important soil water characteristic factor affecting the vegetation community structure in the alpine steppe. [Conclusion] From the view of vegetation community structure, the grazing exclusion time in the alpine steppe in Qinghai Lake may not exceed 7 years, and moderate disturbance might be allowed after 7 years of grazing exclusion.