Spatial patterns of soil bacterial communities in grazing areas of Southwest Spain.

The spatial distribution of soil bacterial communities in agrosilvopastoral systems remains understudied, despite its fundamental role in ecosystem functioning. This study investigates the spatial dynamics of dominant copiotrophic and oligotrophic bacterial phyla in grazing areas of Southwest Spain, focusing on their interactions with land management, soil properties, and environmental covariates. Five management systems; occasional grazing (OG), holistic management (HM), organic farming (OF), conventional rangeland (CR), and conventional grassland (CG) were analyzed across three topographic positions (hilltop, mid-slope, valley bottom), representing a gradient of grazing intensity. A total of 71 soil samples were collected and analyzed using 16S rRNA metabarcoding. Alpha and beta diversity metrics revealed significant shifts in community composition driven by both management and topography, with HM showing higher richness compared to CR and CG. Among dominant phyla, copiotrophic groups such as Proteobacteria and Actinobacteriota were more abundant in upper slope areas and under higher grazing intensity, whereas oligotrophic Verrucomicrobiota was enriched in valley bottoms and under lower grazing pressure. Spatial prediction models based on Random Forest and recursive feature elimination (RFE) identified key environmental drivers, with vegetation indices being more relevant for Proteobacteria and Verrucomicrobiota, and topographic features for Actinobacteriota. RDA and SEM confirmed that animal stocking rate and soil organic matter were major predictors of β-diversity. This study provides novel insights into microbial spatial heterogeneity in Mediterranean grazing systems, highlighting the interplay of management practices, soil characteristics, and topography. The findings underscore the ecological benefits of holistic management in enhancing bacterial diversity and inform strategies for sustainable land use in agrosilvopastoral ecosystems.