Response of the algal-bacterial community to thermal stratification succession in a deep-water reservoir: Community structure, co-assembly patterns, and functional groups.

Thermal stratification in lakes and reservoirs may intensify and become more persistent with global warming. Periodic thermal stratification is a naturally occurring phenomenon that indicates a transition in aquatic ecosystem homeostasis, which could lead to the deterioration of water quality and impaired aquatic communities. However, the responses of communities and associated nutrient cycling processes to periodic thermal stratification are still poorly understood. This study delved into the changes in water quality, algal-bacterial communities, and functional diversity influenced by thermal stratification succession, and their relationship with nutrient cycling. The results indicated that the apparent community dynamics were driven by environmental factors, with ammonium (NH) and nitrate (NO-N) being the most important factors that influenced the algal and bacterial community structure, respectively. Ecological niche widths were narrower during thermal stratification, exacerbating the antagonism of the communities, and stochastic processes dominated community assembly. Then, the complexities of the co-occurrence network decreased with succession. Algal community assembly became more deterministic, while bacterial assembly became more stochastic. Moreover, the roles of algal-bacterial multidiversity in nutrient cycling differed: bacterial diversity enhanced nutrient cycling, whereas algal diversity had the opposite effect. These findings broadened our understanding of microbial ecological mechanisms to environmental change and provided valuable ecological knowledge for securing water supplies in drinking water reservoirs.