Species-dependent effects of seawater acidification on alkaline phosphatase activity in dinoflagellates

Abstract

AbstractGlobal climate change is widely shown to cause ocean acidification (OA) and projected to intensify nutrient limitation. Phosphorus (P) is an essential nutrient for phytoplankton to grow. While dissolved inorganic phosphate (DIP) is the preferred form of P, phytoplankton have evolved alkaline phosphatase (AP) to utilize dissolved organic phosphorus (DOP) when DIP is deficient. Although AP is known to require pH>7, how OA may affect AP activity and hence the capacity of phytoplankton to utilize DOP is poorly understood. Here, we examine the effects of pH conditions (5.5 to 11) on AP activity from six species of dinoflagellates, an important group of marine phytoplankton. We observed a general pattern that AP activity declined sharply at pH 5.5, peaked between pH 7 and 8, and dropped at pH>8. However, our data revealed remarkable interspecific variations in optimal pH and niche breadth of pH. Among the species examined,Fugacium kawagutiiandProrocentrum cordatumhad an optimal pH at 8,Alexandrium pacificum, Amphidinium carterae, Effrenium voratum, andKarenia mikimotoishowed an optimal pH of 7. However, whereasA. pacificum, F. kawagutiiandK. mikimotoihad a broad pH range for AP (7-11),A. carterae, E. voratum, andP. cordatumexhibited a narrow pH range. The response of AP activity ofA. carteraeto pH changes was verified using purified AP heterologously expressed inEscherichia coli. These findings suggest that OA will likely differentially impact the capacity of different phytoplankton species to utilize DOP in the projected acidified and nutrient-limited future ocean.