Abstract
The effect on photosynthesis of N addition to N limited phytoplankton was investigated in several species of algae. Addition of a N source induced suppression of C fixation in some species but not in others. The photosynthetic suppression response upon limiting nutrient addition is taxonomically widespread but appears to be species or strain specific. Discrepancies in previous reports are ascribed to differential phytoplankton responses and not to methodological differences. The physiological and ecological significances of the suppression phenomenon are considered.