Using alkaline phosphatase activity as a supplemental index to optimize predicting algal blooms in phosphorus-deficient lakes: A case study of Lake Taihu, China.

• DOP is highly bioavailable in Lake Taihu, China, especially in Meiliang Bay. • DOP utilization is vital in shaping phytoplankton community in P-deficient waters. • High APA expression is not equal to the high capacities of DOP utilization. • Low algal APA implies the restriction of other factors under P-deficient conditions. • APA can be used to optimize the prediction of algal blooms in P-deficient lakes. Dissolved organic phosphorus (DOP) could be transformed to dissolved inorganic phosphorus (DIP) under phosphorus (P) deficient conditions by various enzymes, among which alkaline phosphatase activity (APA) is regarded as the most important one. To better understand the different response of phytoplankton to DOP and the role of alkaline phosphatase activity (APA) in phytoplankton growth in natural waters, the distribution of P, APA, and phytoplankton density were measured at 12 sites in Lake Taihu, China, in summer, autumn, and winter of 2016. In this study, 34.12% of DOP could be hydrolyzed, indicative of the high bioavailability of DOP in Lake Taihu, especially in Meiliang Bay. More than 70% of enzymatically hydrolyzed DOP came from alkaline phosphatase-hydrolyzed DOP, verifying that APA had a major role in hydrolyzing DOP to fulfill the DIP requirements of phytoplankton, and that phosphomonoesters were the main form of bioavailable DOP in Lake Taihu. Redundancy analysis implied a high capacity of DOP use may be important for species dominance under P-deficient conditions, but high APA expression is not equal to the high capacities of DOP utilization. In this study, phytoplankton density was significantly positive with bulk APA, algal APA and bacteria APA. APA, despite of its complex contributors, is able to increase the amount of bioavailable P for phytoplankton growth. Moreover, algal APA reflects the actual response of phytoplankton to available P under P-deficient conditions. Low algal APA means that other factors limit phytoplankton growth. Increased algal APA means that other limitations get alleviated and algae are in anxious demand for P. Therefore, this paper suggests that monitoring APA can be used as a supplementary indicator to reflect the actual demand for P of algal, thus to optimize the prediction of algal blooms. [ABSTRACT FROM AUTHOR]