Inter- and Intra-Specific Carbon and Nitrogen Assimilation by Dinoflagellate and Diatom Species

Phytoplankton are key components in primary production and their growth is determined mainly by the availability of nitrogen-nutrients in the ocean. The paradigm that phytoplankton prefer ammonium over nitrate when both substrates are present has been tested using ¹⁵N-labelled tracers on cultured diatoms and dinoflagellates isolated from two widespread geographical areas - the Baltic Sea and the Arabian Sea. We found contrary to the paradigm that both taxa preferred nitrate over ammonium and a significant within-species variation in N assimilation. Carbon uptake rates in the same experiments were estimated using ¹³C-labelled tracer.