Spatial and temporal dynamics of the complexity, stability and community assembly of phytoplankton community in a...

Elucidating the spatiotemporal distribution and driving factors of phytoplankton communities in freshwater reservoirs has great significance for early warning and control of harmful algal blooms. The current study aimed to reveal the complexity and stability of phytoplankton communities to explore the ecological processes of phytoplankton community assembly by investigating the spatiotemporal succession of phytoplankton communities under the temporal-horizontal-vertical 3-dimensional scale in the Ankang Reservoir. All the sampling sites were divided into five regions: main channel of the river entering the reservoir, the reservoir, and water column regions at depths of 0-3 m, 5-15 m, and 20-40 m, respectively. The results indicated that the average phytoplankton cell density in summer was the highest (2289.46 × 10⁴ cells/L) and the values in spring and winter were lower than 90 × 10⁴ cells/L. The phytoplankton community was dominated by Cyanophyta in summer (72.9 %), Chlorophyta in autumn (66.0 %), and Bacillariophyta in spring (56.2 %) and winter (56.1 %). The stability and complexity of phytoplankton communities in all regions were much higher in July, August, and October than the other months. Stochastic processes were dominated the phytoplankton community assembly processes in all study regions. Variance partitioning analysis showed that geographical location exhibited higher explanation rate (8 %-24 %) on phytoplankton community structure than the impact of nutrients across all phytoplankton groups (0 %-8 %). Our results suggested that the spatiotemporal heterogeneity of phytoplankton communities in both vertical and horizontal dimensions in reservoir, and emphasized the critical roles of stochastic processes and spatial factors in community assembly.