Species differences in accumulation of nitrogen pools in phytoplankton

The changes in the intracellular concentrations of nitrate, ammonium, free amino acids, protein, DNA, RNA and total nitrogen were measured in batch cultures of seven species of marine phytoplankton as they progressed from being nitrogen sufficient to being nitrogen starved. After several days of nitrogen starvation, either nitrate or ammonium was added to the cultures, and the measurements were continued for 10 to 36 h. By this means it was possible to assess the long-term and short-term changes in cellular nitrogen compounds and how they relate to phytoplankton nitrogen uptake and growth. Considerable species differences were observed in the amounts and kinds of nitrogen compounds which were stored and the degree to which the utilization of these compounds could support growth if the external nitrogen supply is low or variable. Despite the species variation, the results suggest that the concentrations or ratios of a number of intracellular nitrogen compounds can be used to assess the nitrogen deficiency and/or growth rate of natural phytoplankton populations.Contribution No. 1373 from the School of Oceanography, University of Washington and Contribution No. 83006 from the Bigelow Laboratory for Ocean Sciences