DataSheet3_Bacterioplankton Richness and Composition in a Seasonal Urban River.docx

Urbanization and seasonality strongly influence the bacterial composition of the soil. However, aquatic environments such as rivers are understudied owing to their high dynamics and therefore rules relating to more static habitats such as lentic or terrestrial environments may be limited. Here, we compared the spatiotemporal patterns of bacterioplankton communities in the Zhangxi river along a gradient of urbanization using 16S ribosomal DNA identification. The alpha and beta diversity of bacterioplankton showed no significant response to watershed urbanization. A significant difference in predicted functional profiles of the bacterioplankton community was also revealed between the wet and dry seasons. The bacterioplankton community assembly was driven by both deterministic and stochastic processes. Stochasticity was one of the most vital processes affecting the bacterioplankton communities in both wet and dry seasons, explaining over 50% variation in the community by the null model analysis. Bacterioplankton co-occurrence patterns in the river changed with the seasons. More notably, the composition of bacterioplankton communities was inconsistent with alternations of the spatial distance offering meaningful implications for interactions between zero-radius operational taxonomic units and the dynamics of the bacterioplankton communities in surface water. In summary, we found clear patterns of seasonal variations in the bacterioplankton community structures.

城市化进程与季节节律强烈影响土壤细菌群落组成。然而，河流等水生环境因自身高度动态性而鲜有研究，因此适用于静水或陆地等较静态生境的相关规律或存在一定局限性。本研究采用16S核糖体DNA（16S ribosomal DNA）鉴定技术，对比分析了张溪河流域沿城市化梯度分布的浮游细菌群落的时空分布模式。浮游细菌的α多样性与β多样性并未随流域城市化程度呈现显著响应。研究还发现，浮游细菌群落的预测功能谱在丰水季与枯水季间存在显著差异。浮游细菌群落的构建过程同时受确定性与随机性机制共同调控。无论是丰水季还是枯水季，随机性过程均为影响浮游细菌群落的核心过程之一，通过零模型分析（null model analysis）可解释群落变异超50%。河流浮游细菌的共现模式随季节发生显著变化。更值得关注的是，浮游细菌群落组成与空间距离的变化并不一致，这为零半径操作分类单元（zero-radius operational taxonomic units）与地表水中浮游细菌群落动态之间的相互作用提供了重要启示。综上，本研究明确了浮游细菌群落结构存在显著的季节变化规律。