Abstract: We investigated the phytoplankton community of three aquatic vegetation zones in a landscape lake in July 2019 (wet season), October 2019 (normal season), and January 2020 (dry season). The three vegetation zones included Nymphaea tetragona (Nt), Potamogeton crispus (Pc), and Nelumbo nucifera (Nn). We analyzed the spatial and temporal variation of phytoplankton communities and their relationship with environmental factors. The results showed that a total of 41, 46 and 35 phytoplankton species were identified in Nt, Pc and Nn zones, respectively. Most species were belonged to Chlorophyta in three vegetation zones, which accounted for 39.02%, 36.96% and 34.29% of total species number in Nt, Pc and Nn zones, respectively. During the sampling period, the abundance of phytoplankton in Nt, Pc, and Nn zones were (0.59-16.06)×10⁷, (0.59-8.83)×10⁷, and (0.20-1.79)×10⁷ cells·L^-1, respectively. Phytoplankton abundance in Nt and Pc zones followed the order of wet season > normal season > dry season, while Nn zone followed the order of wet season > dry season > normal season. Chlorella sp., Pseudanabaena sp. and Cryptomonas ovata were the most dominant species in each vegetation zone. The Pielou index and Shannon index in three vegetation zones were 0.77-0.86 and 2.08-2.86, respectively, indicating that water quality of the landscape lake belonged to low to medium pollution. Spatially, the main environmental factors affecting phytoplankton abundance in Nt and Nn zones were dissolved oxygen and total nitrogen, while Pc zone was mainly affected by water temperature and total nitrogen. Temporally, the main environmental factor affecting phytoplankton abundance in wet season was total nitrogen, which was changed to dissolved oxygen in dry season. Therefore, the alternation of hydrological periods and vegetation types were the main factors influencing phytoplankton community structure in the three vegetation zones.

Key words: phytoplankton, community structure, aquatic vegetation, landscape lake.