Reyes, A. L.; Rawstern, A. H.; Boughton, E. H.; Guo, Y.; Landau, L.; Qiu, J.; Afkhami, M. E.

Global change drivers are reshaping agroecosystems and their sustained functions worldwide. While soil microorganisms underpin the resilience of these systems, the individual and interactive effects of multiple anthropogenic stressors on microbial community structure and function using large-scale field experiments remain poorly understood. Here, we utilize a full-factorial field experiment in a subtropical agroecosystem to investigate how land-use intensity, cattle grazing intensity, and altered precipitation regimes interact to shape soil microbiomes. Combining microbiome sequencing with network analyses and functional bioinformatics, we evaluated effects of these drivers on prokaryotic and fungal diversity, composition, predicted functional profiles, and community structure. Land-use intensity emerged as the primary driver of microbial responses, explaining 25% and 13% of the total variation in community composition for prokaryotes and fungi, respectively. Compared to intensively managed pastures, semi-natural pastures had significantly different community composition for prokaryotes and fungi and exhibited 22% higher fungal diversity. Semi-natural pastures were enriched with decomposer-associated taxa and metabolic pathways related to energy and lipid metabolism indicating enhanced microbial activity. Surprisingly, intensively managed pastures showed higher network modularity but lower network richness, suggesting a trade-off between community compartmentalization and complexity under intensive land management. Grazing and precipitation manipulations induced core microbiome changes within land-use intensities but had no impact on overall community structure and no significant interactions with land-use. Together, these findings suggest that long-term land-use legacies exert a persistent influence on soil microbial community structure, function, and organization, shaping the context within which other global change drivers operate in subtropical agroecosystems.