INTRACELLULAR CARBON PARTITIONING IN THE COCCOLITHOPHORID EMILIANIA-HUXLEYI

Experiments carried out with the coccolithophorid Emiliania huxleyi ma intained in batch cultures showed that the patterns of photosynthetic carbon metabolism characteristic of this species are: (1) carbon incor poration into proteins only represents about 20% of total carbon fixat ion into organic carbon, (2) protein synthesis in darkness is a signif icant and growth-dependent process, (3) most of the carbon fixed photo synthetically (45-60%) flows towards the lipid fraction, (4) the relat ive 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 C-14 losses during the night generally rep resent 10-13% of gross photosynthesis, and (7) the release of dissolve d organic carbon is related to growth stage and accounts for 2-6% of t he total amount of carbon incorporated photosynthetically. Most of the se patterns of carbon partitioning were validated in natural phytoplan kton assemblages dominated by E. huxleyi during sampling conducted in the Norwegian fjords, The results are interpreted and discussed in ter ms of their potential ecological and biogeochemical significance.