Contrasting Assembly and Network Roles of Abundant and Rare Bacteria in Reservoir and Soil Habitats

Reservoir and adjacent soil are ecologically interconnected yet distinct microhabitats in wetland ecosystems, but direct comparisons of their bacterial community composition and assembly remain limited. In this study, we integrated high-throughput 16S rRNA gene sequencing with statistical, null model, and network analyses to compare the diversity patterns, assembly mechanisms, and interactions of abundant and rare bacterial taxa in both habitats. Soil communities exhibited greater taxonomic diversity but lower overall abundance, while reservoir communities displayed pronounced vertical stratification and soil communities were more spatially homogeneous. Key environmental drivers differed: salinity and nutrient levels structured reservoir communities, whereas nutrient availability and cation exchange capacity dominated in soil. Stochastic processes mainly governed the assembly of abundant taxa in both environments, whereas deterministic selection was more prominent in structuring rare taxa, especially in soil. Co-occurrence network analysis revealed higher connectivity and modularity in soils, with moderate taxa acting as critical connectors between modules, while rare taxa played a pivotal role in sustaining the network stability in reservoir. These findings underscore that distinct assembly mechanisms and ecological roles of abundant and rare bacterial taxa in different wetland microhabitats, providing novel insights to inform effective strategies for wetland conservation and scientific ecosystem management.