Light stimulation of phosphate uptake in marine phytoplankton

A phosphate uptake system responding positively to light would offer the algae a competitive advantage over bacteria, particularly when phosphorus is limiting. Effects of light on phosphate uptake in phytoplankton were investigated in view of conflicting literature reports, to test the hypothesis that both the P status and the light history of the population controlled the response. Maximum stimulation, to about 2.7x dark uptake, was observed at a Strait of Georgia, British Columbia, Canada station where phytoplankton was phosphorus sufficient but light limited. Stimulation was similar, about 1.8 x the dark rate, in the Northern Sargasso Sea, where phytoplankton was probably limited by phosphate but not by light. Minimal stimulation was observed in the Sheepscot Estuary, Maine, USA, where the population appeared to be neither phosphorus nor light limited.