Carbon and nitrogen acquisition by the toxic dinoflagellate Alexandrium tamarense in response to different nitrogen sources and supply modes

Alexandrium tamarense was exposed to increasing nitrogen (N) concentrations from three sources; nitrate, ammonium and urea and two supply modes—pulsed and continuous, and its carbon (C) and N uptake kinetics were examined. Cellular properties and nutrient status of cells were found to be dependent on the type of supply, viz. pulsed vs. continuous. The type of N source and the supply mode induced variability in the C and N assimilation and their interaction. Both the supply mode and concentration of N were important in explaining the observed variability in cellular C and N uptake. Moreover, it was found that A. tamarense had the ability to take up substantial amounts of nitrate, ammonium and urea in the darkness. The present study showed that the changes in the C:N uptake ratios were dependent on the N supply mode rather than the nutrient status of cells. Variability in the C:N uptake ratios indicated unbalanced growth and this kind of uptake–growth strategy could be viewed as an ecological advantage in maintaining uninterrupted growth when nutrients are not supplied continuously. Evaluation of the uptake dynamics of A. tamarense in response to N conditions and the supply mode, enhance our understanding of how anthropogenic activities in global coastal regions can play an important role in controlling the nutrient uptake of this toxic dinoflagellate, and provide insights into the duration of a bloom.