Nutrient uptake kinetics, physiology and toxicity of the harmful dinoflagellata Alexandrium tamarense in response to nitrogen supply mode

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Anthropogenic enrichment in the form of nitrogen (N) is one of the stimuli for the dinoflagellate blooms. N sources are not always supplied to the coastal ecosystem continuously, but also in pulses. When phytoplankton is exposed to different N species including mixed N sources or different N supply mode, some physiological changes including uptake kinetics can be predicted to occur in the calls. In this study, the dints of N sources, concentrations and supply modes on the nutrient uptake kinetic parameters and physiological properties of Alexandrium tamarense were examined. The cellular carbon (C) uptake exhibited different patterns among N sources and also between the two supply modes. This suggests that the C requirement for the syntheses of organic products such as lipid might be dependent on the N utilized. The cellular N uptake was observed to display opposite trend among the two supply modes. This could be due to the difference in metabolic pathways and assimilation of N among N … More spumes. Alexandrium tamarense was able to take up readily the three major forms of N sources supplied, regardless of the type of supply. In general, ammonium induced highest cellular N uptake rates, followed by nitrate and then urea. The present study showed that Alexandrium cells have the capability to switch to different N source upon sudden exposure. In mixed N condition, calls could take up two N species simultaneously. When ammonium plus nitrate (or ammonium plus urea) were supplied in equal concentrations, ammonium was mostly taken up and assimilated. Urea induced higher C: N uptake ratio when compared to those of nitrate and ammonium grown cells. Variability in the C: N uptake ratio indicates major interactions between C and N metabolisms. This interaction may allow A tamarense to maintain high growth under different N environments. Therefore, the form of N supply in coastal environments could play an important role in controlling the nutrient uptake of toxic dinoflagellate and thus contribute to the bloom potential of dinoflagellates. The ability to take up different species of N rapidly and also simultaneously would be an important mechanism that may allow A. tamarense to proliferate and form blooms in marine environments with complex N sources. Less