Hierarchical drivers of soil bacterial assembly and functions across European vineyards: climate dominates, management modulates

Soil bacteria underpin essential ecosystem functions, including nutrient cycling and carbon storage, yet how broad-scale environmental drivers interact with agricultural practices in shaping community assembly remains poorly understood. Here, we investigated how climate, landscape context, soil nutrient stoichiometry and vineyard management interact to shape soil bacterial diversity, predicted functional potential, and interaction networks across major European biogeographic regions. Paired organic and conventional vineyards were sampled in Mediterranean (Spain), oceanic (France), and temperate continental (Austria) climatic zones. Macroclimate, mostly determined by temperature and precipitation gradients, emerged as the dominant filter of bacterial alpha and beta diversity and interaction networks. Additional filters, albeit to a lesser extent, were the surrounding landscape composition (proportion of agricultural vs semi-natural habitats) and soil nutrients (CNP). Despite substantial taxonomic turnover among regions, overall functional capacity remained stable, underscoring strong redundancy across biogeochemical pathways along the climatic gradient. Management exerted secondary, carbon- and nitrogen-cycle function-specific effects. In organic fields, resource-dependent traits such as hydrolytic enzymes and nitrogen fixation were tightly coupled with local nutrient heterogeneity, indicating flexible adjustment to on-site resource pools. Conversely, in conventional fields, carbon‐fixation and oxidoreductases varied primarily with climate and landscape context, suggesting that external inputs decoupled microbes from native stoichiometry and reinforce deterministic, climate-linked assembly. Nitrogen-cycling traits followed similar patterns, with processes like nitrification and denitrification responding more strongly to climatic and spatial gradients. These findings advance a hierarchical model of microbial assembly, where climate and landscape determine the primary constraint, whereas management modulates local processes.