Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton,induced by light intensity and spectral quality

Alkaline phosphatase activity and P uptake were determined in P-limited Dunaliella tertiolecta, Thalassiosira pseudonana, Phaeodactylum tricornumtum, and Prymnesium parvum grown under different light intensities and colors. Both intracellular and extracellular enzyme activities varied with the intensity and quality of light in a species-specific manner. The spectral composition of the light also affected P uptake kinetics. No correlation was found between enzyme activity and V_max both within a species and for pooled data for all four species, indicating that the change in uptake kinetics and enzyme activity was not related to P limitation, but induced by the light conditions. Changes in the optimum N:P ratio induced by light were also not related to P uptake kinetics or enzyme activity. These data suggest that light conditions may in themselves have profound effects on species competition for limiting nutrients. Furthermore, since both alkaline phosphatase activity and P uptake were influenced by the prevailing light conditions we suggest that these parameters be used cautiously when determining the P nutritional status of phytoplankton in nature.Address for reprint requests