Land-use types shape soil bacterial communities, co-occurrence networks, and predicted functions in karst ecosystems.

Understanding how different land-use types shape soil bacterial communities and functions is critical for promoting sustainable land management and ecological restoration in fragile karst regions. This study evaluated the effects of different land-use types (pitaya [HF], maize [MF], sugarcane [SF], and paddy [PF] fields, forestland [FL], and grassland [AF]) on soil bacterial diversity, community composition, functional potentials, and co-occurrence networks in karst regions. The results showed that HF, MF, and PF exhibited the highest bacterial diversity (Shannon index), whereas SF had the lowest possibly because of continuous cropping and fertilization. Variance partitioning analysis revealed that soil bacterial community composition and functional potential were largely explained by the combined effects of land-use type and soil properties (34.8% for composition and 59.7% for functional potential), suggesting that land-use effects on bacterial communities are mainly mediated through changes in soil physicochemical properties. Hierarchical partitioning analysis further identified that soil texture, particularly silt and sand, and pH were the primary factors shaping bacterial community composition, whereas pH was the dominant driver of functional potential. Functional analysis indicated that HF enhanced nitrogen cycling processes, such as nitrification, aerobic nitrite oxidation, and aerobic ammonia oxidation; SF promoted carbon-related functions, including chemoheterotrophy, aerobic chemoheterotrophy, and cellulolysis; and PF favored iron and sulfur respiration. Co-occurrence network analysis demonstrated that HF had the most complex microbial interactions, likely attributable to no-tillage practices and favorable soil conditions, whereas PF showed the lowest network connectivity. Core bacterial groups such as Acidobacteria, Proteobacteria, Chloroflexi, and Actinobacteria, dominated in abundance but also functioned as keystone taxa, suggesting their critical roles in driving nutrient cycling and maintaining ecological stability. These findings suggest that no-till pitaya cultivation may help improve soil microbial diversity, functional potential, and ecological stability in fragile karst ecosystems, indicating its potential as a sustainable agricultural land-use practice. However, long-term monitoring and adaptive management are necessary to ensure sustained soil health.