Carbon Balance Experiments with Marine Phytoplankton

Abstract

Carbon budgets were prepared for eight species of marine phytoplankton organisms in culture and one natural red tide population during 5-hr experiments at 21 C and light intensity 0.07 cal/cm2/min. Net cell carbon increase, dissolved organic carbon excretion, and respiration were each determined by two or more independent methods.In diatoms, net oxygen production gave higher estimates of carbon assimilation than did direct carbon measurements, which were not accounted for by excretion of dissolved organic matter. Carbon-14 assimilation agreed well with the increase in oxidizable particulate carbon and with decrease in dissolved CO2 of the medium, the latter after correcting for excreted organic carbon.Dunaliella tertiolecta excreted a constant fraction of its assimilated carbon regardless of its physiological activity. In diatoms excretion increased as cells became physiologically inactive.Thalassiosira rotula excreted similar amounts of carbon in light and dark. In two other diatoms excretion increased on darkening. In these short-term experiments carbon-14 sometimes gave low estimates of excretion by diatoms probably because both labelled and nonradioactive compounds were released by the cells.