Transient situations in nitrate assimilation by marine diatoms. V. Interspecific variability in biomass and uptake during nitrogen starvation and resupply

Abstract

Nitrate perturbation experiments were carried out on nitrogen-limited and nitrogen 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 nitrate by Chaetoceros affinis, Thalassiosira pseudonana, and Phaeodactylum tricornutum exhibited significant changes over a time scale of hours during nitrogen starvation. V'max increased during the first 3 h for T. pseudonana, but decreased for C. affinis. Upon nitrogen 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 nitrogen deprivation than the other 2 species and was able to exhibit high assimilation numbers and utilize nitrate immediately when starved for less than 48 h.