Ecology Center

Nitrogen requirements sources uptake and metabolism in phytoplankton

Besides being broadly verifiable from observations (see Fig. 4.6b), Eq. (4.15) is consistent with the underpinning physiology. The slope of the equation as plotted in Fig. 4.6a predicts a higher return in chlorophyll for the BAP invested at low availabilities. Thus, 1 |g BAP L-1 is predicted to be capable of supporting up to 6.32 |g chla

Nitrogen is the second element whose relative scarcity impinges upon the ecology of phyto-plankton. As a constituent of amino acids and, thus, all the proteins from which they are syn-thesised, nitrogen accounts for not less than 3% of the ash-free dry mass of living cells (about 0.05 mol N (mol C)-1). This rises to around 7-8.5% in replete cells, capable of attaining rapid growth (0.12-0.15 mol N (mol C)-1, i.e. 6.6-8.2 C : N) (see also Section 1.5.3), and to 10-12% in cells storing condensed proteins. However, molecular C : N ratios of <6 in vegetative cells are usually construed to be symptomatic of carbon deprivation (see Section 3.5.4). Relative to cell phosphorus, the nitrogen content of replete cells is generally in the range 13-19 mol N (mol P)-1; higher molecular ratios (>30 N : P) are indicative of intracellular phosphorus deficiency; lower ratios (<10 N : P) are consistent with nitrogen shortages.