Community dynamics and assembly mechanisms of eukaryotic plankton in two subtropical reservoirs

Abstract:

[Objective] Eukaryotic plankton are key components of a freshwater ecosystem, playing an important role in the food web. This study aims to explore the community dynamics and assembly mechanisms of three differently size-fractionated eukaryotic plankton communities (0.2–200, 0.2–3, and 3–200 μm) in two deep subtropical reservoirs (Shidou Reservoir and Tingxi Reservoir) in Xiamen. [Methods] From 2015 to 2018, samples were collected from both reservoirs in four seasons. The V9 region of eukaryotic 18S rRNA gene was amplified and sequenced to investigate the dynamic changes of eukaryotic plankton communities in the reservoirs. [Results] Overall, the temporal dynamics of dominant phyla of total eukaryotic plankton (0.2–200 μm) showed a strong correlation with that of micro-eukaryotic plankton (3–200 μm) and a weak correlation with that of pico-eukaryotic plankton (0.2–3 μm). Turnover was the main factor driving the temporal dynamics of eukaryotic plankton community composition in the two reservoirs. The proportions of the total number of sequences of the turnover species were higher in Shidou Reservoir than in Tingxi Reservoir in 2016 and 2017, while the opposite pattern was observed in 2018. Deterministic processes played a stronger role in the pico-eukaryotic plankton community assembly in Shidou Reservoir than in Tingxi Reservoir. The concentration of cyanobacterial chlorophyll a was weakly correlated with the eukaryotic plankton community in Tingxi Reservoir, while it was significantly correlated with the eukaryotic plankton community (especially the pico-eukaryotic plankton community) in Shidou Reservoir. [Conclusion] The pico-eukaryotic plankton community was more sensitive to cyanobacterial biomass than the micro-eukaryotic plankton community. The dynamics of the micro-eukaryotic plankton community largely determined the dynamics of the total eukaryotic plankton community. In the context of global changes, efforts should be made to monitor differently size-fractionated eukaryotic plankton and analyze the dynamics of community structure and functions for better understanding and protection of the reservoir ecosystem health and water quality.

Key words:eukaryotic plankton;subtropical reservoir;community assembly;cyanobacteria