Deciphering microbial assembly and coexistence in rivers subjected to long-term reclaimed water replenishment

Reclaimed water recharge into rivers is an important supplementary approach to address water resource shortage in arid and semi-arid areas worldwide. However, the ecology impacts of reclaimed water recharge on the rivers are still unknown, especially for the microbial assemble and species coexistence in different seasons. Here, the evolution of microbiome and its response to different reasons in the Jialu River, which was subjected to long-term reclaimed water recharge, is investigated by using 16S rRNA gene sequencing and multivariate statistical methods. The results indicated that microbial communities exhibited significant temporal heterogeneity across different periods and were negatively correlated with river discharge. Their assembly was primarily influenced by stochastic processes such as dispersal limitation and drift. As the transition occurred from the dry season to the normal season, the role of drift diminished, while the deterministic effects of dispersal limitation and niche selection intensified. The relationships among planktonic bacterial species were primarily positive (cooperative), and the complexity and positive correlations within the ecological network showed a trend of first decreasing and then increasing with the change of seasons. Temperature, dissolved oxygen, and ammonia nitrogen were the main driving forces influencing the structure of microbial communities. In summary, these findings provided insights into the impact of seasonal variations on the microbial community patterns in reclaimed water-supplemented river ecosystems.