Yak grazing intensity alters beta diversity but not alpha diversity of soil microbial community in an alpine meadow

Livestock grazing is a major land use in grassland ecosystems, and over-grazing threatens ecosystem functions and leads to grassland degradation. Soil microbial diversity plays important role in maintaining ecosystem multifunctionality, while how grazing intensity affects the diversity of soil microbial community remains unclear. We examined the effects of yak grazing intensity on soil bacterial and fungal communities via a well-controlled 5-year field experiment in a Tibetan alpine meadow. Our results showed that yak grazing intensity significantly changed soil bacterial and fungal community compositions but not their richness. The co-occurrence network analysis indicated that both soil bacterial and fungal network complexity gradually decreased with increasing yak grazing intensities, as confirmed by the variations in robustness and vulnerability. Meanwhile, soil C:N ratio, soil moisture, dissolved organic nitrogen (DON), NH4+-N, and aboveground biomass (AGB) were significantly correlated with soil bacterial community, and AGB, DON, NH4+-N, and NO3--N were significantly related to soil fungal community, suggesting that yak grazing-intensity induced changes in soil microbial community are mainly controlled by aboveground vegetation and nitrogen cycling-related variables. These results indicate soil microbial community compositions and networks are very sensitive to yak grazing intensity and reveal the tight relationship between microbial functional potentials and soil nitrogen cycling under grazing in alpine meadows. This empirical evidence highlights the necessity to incorporate the module of microbial components under grazing into terrestrial ecosystem models and earth system models in evaluating the consequences of global change.