Intracellular carbon partitioning in the coccolithophorid Emiliania huxleyi

Experiments carried out with the coccolithophorid Emiliania huxleyi maintained in batch cultures showed that the patterns of photosynthetic carbon metabolism characteristic of this species are: (1) carbon incorporation into proteins only represents about 20% of total carbon fixation into organic carbon, (2) protein synthesis in darkness is a significant and growth-dependent process, (3) most of the carbon fixed photosynthetically (45–60%) flows towards the lipid fraction, (4) the relative contribution of lipid-C to cellular biomass is directly related to the amount of calcite-C present as coccoliths, (5) half of the carbon incorporated into polysaccharides during the light period is respired during the night, (6) dark 14C losses during the night generally represent 10–13% of gross photosynthesis, and (7) the release of dissolved organic carbon is related to growth stage and accounts for 2–6% of the total amount of carbon incorporated photosynthetically. Most of these patterns of carbon partitioning were validated in natural phytoplankton assemblages dominated by E. huxleyi during sampling conducted in the Norwegian fjords. The results are interpreted and discussed in terms of their potential ecological and biogeochemical significance.