Abstract
Information on temporal dynamics of phytoplankton communities and their responses to environmental factors can provide insights into mechanisms driving succession of phytoplankton communities that is useful in programs to manage and or remediate undesirable assemblages. Populations of phytoplankton can be controlled by bottom-up factors such as nutrients and temperature or top-down such as predation by zooplankton. Traditionally, taxonomic diversity based on morphologies has been the measure used for analysis of responses to environmental factors. Recently, according to functional groupings, including functional groups (FG), morpho-FG (MFG), and morphology-based FG (MBFG), functional diversity has been used to represent functional aspects of phytoplankton communities. However, to what extent these taxonomic and functional groupings are congruent at seasonal time-scales and the main environmental factors, which drive succession, have remained less studied. Here, we analyzed absolute and relative proportions of a phytoplankton community during a 3-year period in Lake Erhai, a eutrophic highland lake in China. Alpha diversity and beta diversity, as measured by Shannon-Wiener and Bray-Curtis indices of taxonomic grouping and three functional groupings (FG, MFG, and MBFG) were applied to investigate environmental factors determining diversity. Significant, positive relationships were observed between taxonomic diversity and functional diversity that were strongly linked through seasons. In order to exclude the influence of dominant species' tolerance to extreme environments, the dominant species were excluded one by one, and the results showed that residual communities still exhibited similar patterns of succession. This synchronous temporal pattern was not principally driven by the dominant genera (Microcystis, Psephonema, and Mougeotia). Instead, the entire phytoplankton community assemblages were important in the pattern. Most diversity indices of taxonomic and functional groupings were significantly correlated with solar irradiance, but not nutrient concentrations. Because the lake is eutrophic and there were already sufficient nutrients available, additional nutrients had little effect on seasonal taxonomic and functional diversity of phytoplankton in Lake Erhai.
Highlights
Phytoplankton, including planktonic algae and cyanobacteria, are primary producers in aquatic ecosystems, which play key roles in providing food for and affecting other organisms, and in turn are regulated by interactions with other organisms (Hutchins and Boyd, 2016; Kohlbach et al, 2016)
Concentrations of NH4-N were greatest during summer, while concentrations of dissolved inorganic phosphorus (DIP) were greater during spring and autumn, Secchi depth (SD) was maximum in spring and T reached its maximum in August
Communities of cyanophyta were by the genera Microcystis and Aphanizomenon, and Chlorophyta was dominated by genera Psephonema and Mougeotia (Figure 3A-Genus)
Summary
Phytoplankton, including planktonic algae and cyanobacteria, are primary producers in aquatic ecosystems, which play key roles in providing food for and affecting other organisms, and in turn are regulated by interactions with other organisms (Hutchins and Boyd, 2016; Kohlbach et al, 2016). Succession of phytoplankton is related to multiple environmental factors such as nutrient concentrations, temperature, and quantity and quality of light in aquatic systems (Malik and Saros, 2016; Paerl et al, 2016; Thomas et al, 2017). Understanding mechanisms of phytoplankton succession and investigating responses in species composition to environmental factors can improve predictive power for phytoplankton responses to environmental changes
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