Extrc~celhh release of carbon by marine phytoplankton; a physiological approach’

The production of soluble, ‘%-labeled organic material from H “C0,- by cultures and natural populations of marine phytoplankton has been examined with particular attention to cxperimcntal technique. Extracellular release is a normal f;mction of healthy cells, is closely related to photosynthetic rate, and is a minor component (up to 5 pg C-liter-‘ah-‘) of total primary productivity in coastal waters. Time-course studies and chemical cell-fractionations indicate that newly synthesized organic “‘C is distributed among various cell polymers and the extracellular medium from a rapidly labeled, soluble intracellular pool of small molecules. The rate of supply of carbon to this pool may determine the relative rate of release. Extra-cellular “C appearing during transient light shock may preferentially arise from rapidly mo-Ijilized polysaccharide and is not simply the result of cell lysis. The l&C method of measuring primary production in the oceans (Steemann Nielsen 1952) provided a sensitive pro-cedure with which to trace carbon flow dllring photosynthesis, It was a great im-provement over earlier methods in which small incremental increases in dissolved oxygen or particulate organic carbon were measured. However, it was soon apparent that any “‘C-labeled organic ma-terial released from phytoplankton cells was not measured by the filtration meth-ods then in use (Fogg 1958). Studies in-dicated that up to 70 % of the total 14C recently incorporated by freshwater phy-toplankton could appear outside the cel