Abstract: Bacterial community succession in river ecosystems exhibits obvious habitat dependence. In this study, we examined the succession characteristics, potential ecological function, co-occurrence network, and assembly mechanisms of bacterial community in different reaches of the Fenhe River main stream. The results showed that bacterial abundance and  α-diversity in the upper and middle reaches were significantly higher than those in the lower reaches (P<0.05). Phyla of Proteobacteria, Firmicutes and Actinobacteria were dominant, which could be widely involved in the biogeochemical cycles of diverse elements in the wetland soil, such as carbon, nitrogen, sulfur and variable-valence metals (iron and manganese). Bacterial community composition and potential functions exhibited significant distance-decay patterns across different regions (P<0.01). Stochastic processes dominated bacterial community assembly, particularly in the middle reaches. Connections among bacterial taxa in the middle reaches were relatively weak, whereas the complexity and stability of co-occurrence networks in the upper and lower reaches increased with the enhancement of deterministic processes. In general, the diversity and co-occurrence network of bacterial community showed obvious spatial heterogeneity in the wetland soil of Fenhe River, which was mainly regulated by stochastic processes.

Key words: river ecosystem, bacterial community, potential function, co-occurrence network, succession characteristics