Soil bacterial communities are central to nutrient cycling and fertility, yet the long-term ecological consequences of converting forest to orchard systems remain poorly understood. This study investigated the impacts of forest-to-orchard land-use conversion and prolonged orchard cultivation (9 and 16 years) on soil nutrient dynamics and bacterial community structure in a subtropical red soil hilly region of southern China. Soil physicochemical properties, bacterial community composition, co-occurrence networks, and predicted metabolic pathways were analyzed to assess microbial responses. Land-use conversion significantly increased soil nutrient availability, especially available phosphorus, which reached 298.86 mg·kg -1 in the 16-year orchard. Orchard establishment also shifted bacterial community composition, with Proteobacteria becoming more abundant and Acidobacteria declining. Co-occurrence network analysis revealed initially more complex microbial interactions in orchard soils, including the emergence of Verrucomicrobiota taxa absent from forest soils, but network complexity declined after 16 years of cultivation. Soil organic matter and available phosphorus were key drivers of changes in community structure. Predicted functional profiles indicated a clear metabolic shift from nutrient-conserving pathways (e.g., organic nitrogen degradation prevalent in forest soils) to enhanced biosynthesis and fermentation pathways in orchard soils. This shift reflects a transition in microbial strategy from resource-conserving to fast-cycling under prolonged cultivation. Overall, these findings highlight the strong influence of land-use change and soil nutrient status on microbial community assembly and function, and underscore the need for nutrient-sensitive management to sustain soil health and ecosystem services in orchard systems.