Biotic Interaction Underpins the Assembly Processes of the Bacterial Community Across the Sediment–Water Interface in a Subalpine Lake

The sediment-water interface is the most active region for biogeochemical processes and biological communities in aquatic ecosystems. As the main drivers of biogeochemical cycles, the assembly mechanisms and the distribution characteristics of microbial communities at this boundary remain unclear. This study investigated the microbial communities across the sediment-water interface in a natural subalpine lake in China. The results indicated that the diversity of bacterial communities in middle sediment was significantly higher than that in overlying water and other sediments (<i>p</i> < 0.001). Pearson's correlation analysis indicated that the diversity was significantly influenced by biotic factors (e.g., diversity of fungus, protozoan and alga) and physicochemical parameters (e.g., total carbon, total organic carbon, nitrate, ammonium and pH) (<i>p</i> < 0.01). Null model analysis revealed that the homogeneous selection dominated the assembly of the bacteria community in sediment, whereas the heterogeneous selection dominated that in overlying water. The least squares path analysis showed that interactions between protozoa and bacteria had a greater impact on bacterial community assembly (<i>p</i> < 0.001). Important taxa influence the assembly by regulating biotic interactions. These findings provided a basis for understanding the importance of biotic interactions in maintaining subalpine lakes' ecosystems across the sediment-water interface.