Effects of turbulence on alkaline phosphatase activity of phytoplankton and bacterioplankton in Lake Taihu

Abstract

Alkaline phosphatase (AP), an inducible and hydrolytic enzyme, plays a key role in the biogeochemical cycle of phosphorus (P) in lakes. Activity and regulation of AP has been suggested to be affected by hydrodynamic turbulence. However, many aspects of the coupling of the AP activity (APA) and turbulence are still to be investigated and understood. In this study, mesocosm experiments were carried out to further understand the effects of turbulence on APA and the relative contribution of the different microbial groups to the total APA (TAPA). Specifically, we focused on evaluating the APA of phytoplankton (2–112 µm) and bacterioplankton (0.2–2 µm) and its relationship with P fractions under four turbulence levels. Results showed that turbulent conditions enhanced planktonic APA (PAPA) which dominated TAPA by comprising 66–93% of the total fraction. In particular, PAPA was almost two times higher in the turbulence treatments than in still-water control. On the other hand, bacterioplanktonic APA (BAPA) decreased which could be associated with the competitive advantage of bacteria in nutrient-limited conditions due to surface-to-volume ratio. The results suggest that turbulence can accelerate the biogeochemical cycle of P and plays an important role in P strategies of plankton.