Moderate grazing enhances soil nutrient cycling in desert grasslands through microbial community assembly at the patch scale

Desert steppes are highly sensitive ecosystems, yet how long-term grazing regulates soil microbial assembly and ecological functions at the patch scale remains unclear. Using a 10-year in situ grazing experiment, we investigated microbial communities within native Stipa breviflora patches to evaluate these micro-ecological responses. Bacterial and fungal communities exhibited asynchronous, non-monotonic responses to grazing intensity. Light grazing primarily stimulated bacterial α-diversity and predicted carbon/nitrogen turnover, which was associated with the input of labile resources. In contrast, moderate grazing increased substrate heterogeneity, shifting fungal communities toward stronger deterministic assembly and specialist selection. Furthermore, the microbial network restructured under moderate grazing to favor core functional taxa, potentially promoting nitrogen retention. These patch-scale evaluations reveal a decoupling of microbial diversity and predicted functions, suggesting that functional specialization and synergy are more closely linked to nutrient cycling potential than simple taxonomic richness. This study advances our understanding of grazing ecology by indicating that maintaining patch-scale functional interactions is essential for sustaining soil nutrient cycling in desert steppes under grazing pressure.