TRANSIENT SITUATIONS IN NITRATE ASSIMILATION BY MARINE DIATOMS .5. INTERSPECIFIC VARIABILITY IN BIOMASS AND UPTAKE DURING NITROGEN STARVATION AND RESUPPLY

NO3- perturbation experiments were carried out on N-limited and N-starved marine diatoms under low light intensity to simulate the injection of deep water in the euphotic zone at the level of the thermocline. The potential uptake rate (V''max) of NO3 by Chaetoceros affinii, Thalassiosira pseudonana and Phaeodactylum tricornutum exhibited significant changes over a time scale of hours during N starvation. V''max increased during the first 3 h for T. pseudonana, but decreased for C. affinis. Upon resupply, the direction of change in V''max was dependent on the species and the duration of incubation. Even though biomass parameters such as chlorophyll indicated a rapid cellular degradation. C. affinis was better adapted to N deprivation than the other 2 spp. and was able to exhibit high assimilation numbers and utilize NO3- immediately when starved for < 48 h.