Enhanced utilization of organic phosphorus in a marine diatom Thalassiosira weissflogii: A possible mechanism for aluminum effect under P limitation

Abstract

Although many studies have reported the aluminum (Al) impacts on freshwater organisms and terrestrial plants in acidic and neutral pH media, little information is available on the effects of Al on organisms in the alkaline seawater. In this study, the Al effects on marine phytoplankton were investigated by growing the axenic diatom Thalassiosira weissflogii in seawater media amended with varied nutrient levels. Under phosphorus (P) limited conditions, Al enrichment resulted in an enhanced diatom growth and higher biomass accumulation, as well as the maintenance of high diatom biomass during the stationary phase. The diatom displayed higher cellular alkaline phosphatase activity (APA) under Al-enriched and P-limited conditions, which was responsible for the increased uptake of dissolved organic phosphorus (DOP). Lower dissolved APA was observed in the Al-enriched culture. In contrast, Al addition did not change the phosphate speciation in seawater or the diatom uptake of dissolved inorganic P (DIP) at low concentration, but instead made the diatoms uncompetitive under high DIP conditions. The results strongly indicated that Al treatment increased the proportion of the diatom cellular APA and their utilization efficiency of DOP, which may partly account for the beneficial effects of Al on the diatom under P-limited conditions. It is thus likely that Al may influence the ocean carbon cycling by promoting the phytoplankton utilization of DOP.