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.
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