ABSTRACT: The effect of variable CO₂ concentrations on the elemental composition (C:N:P) of marine diatoms was investigated in 2 strains of Skeletonema costatum (Grev.) Cleve. Five or 6 concentrations of dissolved molecular carbon dioxide [CO₂ (aq)], ranging from 0.5 to 39 µmol l^-1, were applied in dilute batch cultures. In both strains, elemental ratios were clearly dependent on [CO₂ (aq)]. With decreasing CO₂ concentrations, a decline in C:P and N:P and an increase in C:N was observed. The close correlation between C:P or N:P and [CO₂ (aq)] corresponded to a ca 45 to 65% decrease in elemental ratios from highest (>=30 µmol l^-1) to lowest (ca 1 µmol l^-1) CO₂ concentrations. C:N at low [CO₂ (aq)] was up to 24% higher than at high [CO₂ (aq)]. To date, the elemental composition of marine phytoplankton has been considered to be independent of CO₂ availability. If dependency of the C:N:P ratio on [CO₂ (aq)] proves to be a general phenomenon in marine phytoplankton, changes in the elemental composition may be expected in response to the currently observed increase in partial pressure of atmospheric CO₂.

KEY WORDS: Redfield ratio · CO₂ · Phytoplankton · Marine diatoms · Cell stoichiometry

Published in MEPS Vol. 155 (1997) on August 28
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997