Abstract: Soil microorganisms play a crucial role in alpine grassland ecosystem as indicators of environmental change. Rest-grazing in spring has been shown to effectively curb grassland degradation, and while the effects on plants and soil have been widely studied, the response of soil microbial communities and the underlying driving factors remain unclear. In this study, two types of winter-spring pastures, steppe meadow (StM) and swamp meadow (SwM), were conducted for rest-grazing and grazing in spring, and vegetation community characteristics, soil properties and microbial community composition were measured to investigate the response of soil microbial communities to rest-grazing and its mechanisms. The results showed that rest-grazing in spring significantly increased above-ground biomass and soil organic carbon in alpine grasslands. In the steppe meadow, microbial groups were lower in the first year of rest-grazing compared to grazing but higher in the second year. In the swamp meadow, microbial groups and the ratio of Gram-positive to Gram-negative bacteria were higher under rest-grazing than under grazing. Stress indices in both grassland types were lower under rest-grazing than under grazing. Fungi showed an increasing trend with above-ground biomass (P < 0.05), while total PLFAs, bacteria, and actinomycetes increased with below-ground biomass (P < 0.05). Variance partitioning analysis (VPA) revealed that the combination of soil and vegetation properties explained 40.87% of the variation in the soil microbial community. Redundancy analysis (RDA) indicated that species diversity (Simpson index), vegetation coverage, soil total phosphorus, and bulk density were significant influencing factors, with species diversity explaining the largest proportion of variation (60%). In summary, rest-grazing in spring can beneficially affect the soil microbial community by improving plant diversity and restoring soil properties in alpine grasslands.

Key words: rest-grazing in spring, soil microbial community, environmental factors, alpine grassland, Qilian Mountains