Seasonal changes driving shifts in microbial community assembly and species coexistence in an urban river.

Microbial communities play a vital role in urban river biogeochemical cycles. However, the seasonal variations in microbial community characteristics, particularly phylogenetic group-based community assembly and species coexistence, have not been extensively investigated. Here, we systematically explored the microbiome characteristics and assembly mechanisms of urban rivers in different seasons using 16S rRNA gene sequencing and multivariate statistical methods. The results indicated that the microbial community presented significant temporal heterogeneity in different seasons, and the diversity decreased from spring to winter. The phylogenetic group-based microbial community assembly was governed by dispersal limitation and drift in spring, summer, and autumn but was structured by homogeneous selection in winter. Moreover, the main functions of nitrification, denitrification, and methanol oxidation were susceptible to dispersal limitation and drift processes, whereas sulfate respiration and aromatic compound degradation were controlled by dispersal limitation and homogeneous selection. Network analyses indicated that network complexity decreased and then increased with seasonal changes, while network stability showed the opposite trend, suggesting that higher complexity and diversity reduced community stability. Temperature was determined to be the primary driver of microbial community structure and assembly processes in different seasons based on canonical correspondence analysis and linear regression analysis. In conclusion, seasonal variation drives the dynamics of microbial community assembly and species coexistence patterns in urban rivers. This study provides new insights into the generation and maintenance of microbial community diversity in urban rivers under seasonal change conditions.