Plant and soil responses to grazing intensity drive changes in the soil microbiome in a desert steppe

Background and aims: Grazing pressure can degrade environmental quality and disrupt ecosystem structure and functions, while its potential effect on the soil microbiome is unclear. Method: We evaluated the effects of grazing intensity (CK: no grazing, LG: light grazing, MG: moderate grazing, HG: heavy grazing, and OG: overgrazing) on soil microbial diversity and community composition in a desert steppe. Results: Different microbial communities were found under different grazing intensities, resulting from differences in soil moisture, nutrients and plant species. Alpha-diversity in the bacterial community was strongly correlated with soil organic content (SOC) and soil water content, while the alpha-diversity of the fungi depended on the SOC and pH of the soil. Grazing treatments LG, HG and OG caused strong shifts in bacterial and fungal community composition. Heavy grazing (HG and OG) significantly increased the relative abundances of Chloroflexi, Gemmatimonadetes, and Firmicutes bacteria, while light grazing (LG) significantly decreased the relative abundance of Actinobacteria. Grazing intensities HG and OG increased the relative abundances of certain fungi (e.g., Ascomycota). Co-occurrence network analysis indicated that bacterial communities had a more complex network than fungal communities. A multivariate regression tree demonstrated that the bacterial community responded to grazing via changes in the biomass of perennial plant species and SOC, whereas the SOC and pH value altered the fungal community composition. Conclusions: Our findings indicate that different grazing intensities can initiate different changes in the soil microbiome; sustainable grazing intensity over decades facilitates the recovery of primary productivity and ecosystem functions in a desert steppe.