Phosphate Uptake by the Oceanic Dinoflagellate Pyrocystis Noctiluca1

Phosphate uptake by P‐replete and P‐depleted Pyrocystis noctiluca (Murray) Schütt grown at different ambient N:P ratios was multiphasic between 0.1 and 100 μM PO43‐. Within each of the kinetic phases, the saturated uptake rate (Vmax), but not the half saturation constant (Km) was affected by the cellular‐P status and light. Uptake rates in the dark were ca. 50% of that in the light and respiratory activity accounted for the observed basal uptake. The combination of multiphasic uptake, and the uncoupling of short term transient uptake from growth resulting in maximum specific uptake rates of 50 h−1 may help explain the abundance of P. noctiluca in oligotrophic regions.