Rainfall-driven shifts in eukaryotic microbial communities: Enhanced stochasticity and altered co-occurrence networks in the Fen River

Rivers are fundamental components of the Earth's hydrological system, and their hydrogeochemical processes play a critical role in maintaining the stability of ecological communities and socio-economic development. In this study, we employed 18S rRNA gene sequencing, neutral community modeling, null model analysis, and co-occurrence network analysis to investigate shifts in the composition and assembly processes of eukaryotic microbial communities before and during a rainfall event. Taxonomic analysis revealed that Chlorophyta and Rotifera were the dominant eukaryotic taxa. Compared with pre-rainfall conditions, the relative abundance of Chlorophyta increased by 13.53 % during rain, while that of Rotifera decreased by 17.66 %. Among the rare taxa, Chlorophyta and Chytridiomycota accounted for relatively high proportions. Our findings indicate that stochastic processes primarily drive the assembly of riverine eukaryotic microbial communities, with rainfall events amplifying the influence of stochasticity and diminishing the influence of deterministic processes. Rainfall substantially increased the strength of dispersal limitation, which had a major effect on rain-associated communities with broader ecological niche breadths. Rainfall also induced significant shifts in ecological niches and destabilized co-occurrence networks among eukaryotic microbes, as evidenced by pronounced changes in node degree metrics. Our findings provide valuable insights into the structure, dynamics, and ecological processes of eukaryotic microbial communities under the influence of rainfall and enhance our understanding of freshwater microbial ecology.