Hydrological Regime Shifts Reshape Assembly Dynamics of Multi-Trophic Microbial Communities in Pumping Station Forebays.

Multi-trophic microbial community assembly and interactions in the forebays of pumping stations have remained poorly understood. In this study, 16S and 18S rRNA sequencing was carried out to reveal the diversity, network structure, assembly processes and environmental drivers of multi-trophic microbial communities across normal and wet seasons in the pumping stations of the Qinhuai River Basin. The results showed that microbial diversity and community composition differed significantly between the two hydrological periods across all four trophic groups. Co-occurrence network analysis indicated that the wet season network displayed greater complexity, connectivity and stability compared with the normal season network. Community assembly analyses revealed that dispersal limitation dominated in both seasons, whereas the relative contribution of homogeneous selection increased substantially during the wet season. Moreover, trophic transfer efficiencies were significantly correlated with β-nearest taxon index (βNTI) values, suggesting an association between cross-trophic interactions and assembly processes. Environmental analyses further showed that eukaryotic communities were jointly regulated by temperature (T), nitrogen nutrients and pH, whereas bacterial communities were mainly driven by T. These findings strengthen the understanding of how hydrological fluctuations regulate multi-trophic microbial communities through the combined effects of environmental filtering and trophic interaction restructuring in pumping station ecosystems.