Spatiotemporal dynamics of the bacterioplankton community in a subtropical estuary: biogeographic patterns and assembly processes

Unveiling microbial biogeography and community assembly mechanisms remains a significant challenge in microbial ecology. Specifically, our understanding of bacterial community composition and its assembly processes under spatial and seasonal variations in estuaries remains limited. Here, we employed 16S rRNA high-throughput gene sequencing to investigate biogeographical patterns, assembly processes, and co-occurrence networks of surface bacterial communities along the Changjiang River Estuary, China, across seasons. Our findings demonstrate that both spatial and seasonal variations shape bacterioplankton community structure. Co-occurrence networks exhibited greater discrepancies across seasons compared to spatial variation, with the summer network showing reduced complexity than other seasons. Stochastic processes dominated community assembly (explaining 53.25% of variation), likely driven by intensified Changjiang River flow, which enhanced both water connectivity and stochastic bacterial dispersal. This study demonstrates spatial and seasonal variations in bacterioplankton community structure, assembly processes, and co-occurrence networks within an estuarine ecosystem, highlighting the significant role of stochastic processes in structuring this community.