Structural changes and assembly mechanisms of microbial communities during rapid sedimentation of Yellow River sediments

Microbial communities are essential for the biogeochemical cycles in aquatic ecosystems. The effects of sediment depositional processes on the microbial community characteristics in the Yellow River have not been extensively studied at the in-situ macroscopic scale. Since the Yellow River diversion reservoir has the sedimentation pond, it can be used as a natural experimental area. This study investigated changes in microbial community structures, functions, and assembly mechanisms under sediment deposition by analysing 26 water and sediment samples. The results showed that during rapid sediment deposition, different community structures formed between the water body and the sediment (Analysis of similarities, P<0.01), and the variability between them increased with increasing water depth. Sediments are more closely associated with carbon, nitrogen, and sulfur cycling processes, while water is more closely associated with light reactions. Under changing sediment concentrations, the microbial community diversities, community compositions, and functions changed significantly. Actinobacteria and Cyanobacteria were the species responsible for the significant differences in the microbial communities in the water, with linear discriminant analysis scores of 4.478–4.724 and 4.427–5.007, respectively. Water temperature, NH₄⁺-N, and electrical conductivity were the most critical factors that affected the microbial community structures. During the rapid deposition of sediments, microbial community assembly was dominated by stochastic process. This study may provide a reference for exploring the mechanism of microbial community changes in reservoirs under the dynamic hydrological conditions of the Yellow River.