CARBON, NITROGEN, AND CARBOHYDRATE FLUXES DURING THE PRODUCTION OF PARTICULATE AND DISSOLVED ORGANIC-MATTER BY MARINE-PHYTOPLANKTON

Although the principal source of marine organic matter is phytoplankto n, experimental data on carbon and nitrogen mass balance during their growth cycle are lacking. Phytoplankton from diverse taxonomic groups (Synechococcus bacillaris, Phaeocystis sp., Emiliania huxleyi, Skeleto nema costatum) were grown in synthetic seawater media, and changes in particulate and dissolved carbon, nitrogen, and carbohydrates were fol lowed for 14 d. There was a close molar balance between dissolved inor ganic carbon (DIG) uptake and total organic carbon (TOC) production in all phytoplankton except Emiliania, which synthesizes carbonate-conta ining coccoliths. Rates of dissolved organic carbon (DOC) production d uring phytoplankton growth ranged from 5 to 13 mu M DOC d(-1) (0.01-0. 06 pmol DOC pM cell C-1 d(-1)) and constituted a substantial (10-32%) fraction of TOC production. The carbohydrate content of both the parti culate and dissolved pools increased over the growth cycle and constit uted 18-45% and 26-80% of TOC, respectively. The dissolved carbohydrat e pool was predominantly composed of poly saccharides (70-94%). Despit e some species-specific variability, phytoplankton cellular (particula te) and extracellular (dissolved) organic matter C:N ratios did not de viate far from Redfield values. However, phytoplankton synthesized com positionally distinct peals of high molecular weight dissolved organic matter (>1,000 Da, average C:N ratio similar to 21) and low molecular weight dissolved organic matter (<1,000 Da, average C:N ratio similar to 6.0).