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Phosphomonoesterase and phosphodiesterase activities and their regulation during dinoflagellate blooms under different external phosphate conditions

Kaixuan Huang, Zhou Wang, Jinzhou Tan, Dazhi Wang, Xinfeng Dai, Jingyi Cen, Linjian Ou*, Songhui Lu

*Corresponding author:

ABSTRACT: Phosphatases play a crucial role in the recycling of organic phosphorus and determine primary production and phytoplankton communities in seawater, especially in phosphate-depleted coastal waters. The present study analyzed the spatiotemporal variations in phosphomonoesterase (PMEase) activity (PMEA) and phosphodiesterase (PDEase) activity (PDEA) during two dinoflagellate blooms that occurred in two different coastal waters of Fujian Province, East China Sea, that differed in their external phosphate conditions. Together with environmental variables and with a specific focus on the availability of different phosphorus forms in the seawater, the regulation of both phosphatases was studied. The results showed that dissolved organic phosphorus (DOP) was the major phosphorus source during blooms, especially in phosphate-depleted environments. Labile DOP accounted for more than 50% of the DOP, among which phosphomonoester (PME) and phosphodiester (PDE) accounted for 75–94% and 6–25% of the DOP, respectively. PMEA and PDEA were highly correlated, both increasing during blooms with a fixed PMEA:PDEA ratio of 2.5 under both external phosphate conditions. Both PMEA and PDEA were negatively correlated with dissolved inorganic phosphorus (DIP) when phosphate was depleted, but they were positively correlated with DOP regardless of the external phosphate conditions. During dinoflagellate blooms, temperature and phytoplankton biomass were the dominant variables determining both phosphatase activities under phosphate-depleted conditions, whereas the availability of DOP was the dominant variable determining both phosphatase activities under phosphate-replete conditions. This study suggested the importance of phosphatases in recycling DOP and indicated the similar regulation of PMEA and PDEA during dinoflagellate blooms.