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Re-establishing submerged vegetation is considered an important tool to restore shallow eutrophic lakes.A whole year comparative field study was performed in a eutrophic lake and its connected pond with Pota-mogeton crispus in order to determine the effects of the growth and senescence of submerged macrophytes on structure of phytoplankton.P.crispus improved the water quality at the growing season in terms of improving transparency,decreasing total phosphorus,soluble reactive phosphorus(SRP)and chlorophyll a concentra-tions and slowering turnover rate of dissolved organic phosphorus(DOP).Meanwhile,dominant species shift from Chlorophyta to Diatom.Notably,senescence and decomposition of P.crispus in late spring resulted in an abrupt increase of DOP,providing a suitable growing environment for Euglena and dinoflagellates and a Peridiniopsis bloom occurred owing to their advantage in utilizing DOP.Peridiniopsis excreted phosphatase as evidence by simultaneously in situ enzyme labelled fluorescence(ELF)labelling and main alkaline phos-phatase activity contributed by large particles,suggesting that the dominance of dinoflagellate with low SRP is enabled by its ability to efficiently hydrolyze DOP.Under the scenario of worldwide application of re-es-tablishing submerged vegetation,our results provide the evidence of the negative environmental effects that occurred when transplanting P.crispus to recover a eutrophic lake.