Seasonal dynamics of periphytic algal community assembly driven by climate-dominated multiscale mechanisms in subtropical Rivers

Periphytic algae are crucial bioindicators of aquatic ecosystem health and key drivers of nutrient cycling in subtropical rivers. However, their community assembly mechanisms, seasonal dynamics, and multiscale regulation by environmental factors remain poorly understood. Here, multi-season sampling was conducted across five representative rivers in the Poyang Lake Basin of China to explore the spatiotemporal patterns and regulatory mechanisms of periphytic algal community assembly. We integrated β-diversity partitioning, normalized stochasticity ratio (NST) analysis, random forest, and partial least squares path modeling. A total of 194 species spanning seven phyla of periphytic algae were identified, with Bacillariophyta, Chlorophyta, and Cyanophyta as the dominant groups (>95% of total species). Species turnover contributed substantially to community β-diversity (79.4%). Stochastic processes governed community assembly across three ecologically active seasons (NST = 0.59), with distinct seasonal shifts. High temperatures in summer strengthened deterministic environmental filtering, leading to weakened stochastic assembly processes in several rivers. Climatic factors, especially mean monthly precipitation, showed the great effects on community β-diversity and its components among the measured variables. Climatic factors regulated community assembly both directly and indirectly by altering water environment and nutrient levels, which overwhelmed the influence of spatial factors. This study highlights that seasonal climatic disturbance acts as the core driver of periphytic algal community assembly in subtropical rivers. The findings could inform targeted seasonal management for biodiversity conservation in the Poyang Lake Basin.