[Changes of Phytoplankton Community Structure and Influencing Factors in Erhai Lake]

Phytoplankton is the most important primary producer in lakes， and its community structure can reflect the changes in lake ecosystems. In order to understand the changes of phytoplankton functional community structure and its influencing factors in Erhai Lake， a plateau lake， the phytoplankton community composition， water quality changes， and zooplankton and zoobenthos abundance in Erhai Lake were continuously observed every quarter from 2022 to 2023. The results showed that 7 phyla and 81 genera of phytoplankton were identified from 2022 to 2023. Bacillariophyta density and biomass decreased， while cyanobacteria， chorophyta， and cryptoalgae increased. The density of phytoplankton was low in spring and high in autumn， and the biomass reached its peak in summer. The density and biomass of algae were higher in the northern lake area and increased in the central and southern parts of the lake. The Shannon Wiener （H） diversity index and Pielou （J） evenness index were 0.82-2.43 and 0.34-0.97， respectively， which decreased. There were 16 genera of dominant phytoplankton in Erhai Lake， which were divided into 13 functional groups. The phytoplankton community structure changed from P functional groups to M， H1， and K functional groups. Phytoplankton evolved from Fragilaria sp. and Dolichospermum sp. to Melosira sp.， filamentous cyanobacteria， and Microcystis sp.. The number of dominant functional groups increased， and the change of functional community structure was unstable. Water temperature （WT）， turbidity （NTU）， pH， water surface wind speed （WS）， total nitrogen （TN）， electrical conductivity （EC）， and transparency （SD） were the key environmental factors affecting the changes of phytoplankton functional groups. The biomass of the P functional group was positively correlated with SD and EC； the density of the M and H1 functional group was significantly positively correlated with pH， NTU， and WT； and the density and biomass of the K functional group were positively correlated with NTU， WT， and WS. Cladocera and Copepoda zooplankton， as well as aquatic insects， gastropods， and crustacean benthos， were positively correlated with the H1， S1， S_N， and P functional groups， while protozoa， bivalves， oligochaetes， and leeches were positively correlated with the K， C， B， X2， and Lo functional groups. The T and E functional groups were positively correlated with rotifers and protozoa. The correlation between the M and Y functional groups and zooplankton and zoobenthos was not obvious or negatively correlated.