Impact of Land Use Conversion on Soil Environmental Factors and Bacterial Community Composition in the Red Soil Hilly Region of Southern China

ABSTRACT Soil bacterial communities, which are vital for nutrient cycling and fertility, may experience intensified alterations under forest‐to‐orchard conversions in the acidic, nutrient‐deficient red‐soil hills of southern China, yet the long‐term impacts of such changes remain poorly understood. This study investigated the effects 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. The soil physicochemical properties, bacterial community compositions, co‐occurrence network, and predicted metabolic pathways were analyzed to assess microbial responses. Land use conversion from forestland to a 16‐year orchard markedly enhanced soil nutrient availability, with soil organic matter increasing from 16.09 g·kg −1 in forest soil to 21.92 g·kg −1 in the soil of the 16‐year‐old orchard and the available phosphorus concentration increasing from 45.87 mg·kg −1 to 298.96 mg·kg −1 , indicating substantial nutrient enrichment under orchard cultivation. Orchard establishment also shifted the bacterial community composition, with the abundance of Proteobacteria increasing and that of Acidobacteriota decreasing. Co‐occurrence network analysis revealed initially more complex microbial interactions in orchard soils, including the emergence of Verrucomicrobiota taxa that were absent from forest soils, but the network complexity declined after 16 years of cultivation. Soil organic matter and available phosphorus were key drivers of the changes in community structure. The 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 reflected a transition in microbial strategy from resource‐conserving to rapid cycling under prolonged cultivation. Overall, these findings highlight the strong influence of land use conversion and soil nutrient status on microbial community assembly and function, and underscored the need for nutrient‐sensitive management to sustain soil health and ecosystem services in orchard systems. These insights offer an ecological guide for optimizing fertilization and organic‐matter management to improve soil resilience and sustain the productivity of red‐soil hilly orchards converted from forests.