Exudation of organic carbon by marine phytoplankton: dependence on taxon and cell size

We determined the relationship between photosynthetic production of dissolved organic carbon (OC) and phytoplankton cell size and taxonomic composition in cultures of marine phytoplankton at 3 different growth stages. We measured OC exudation in 22 species belonging to 5 phyla and spanning >7 orders of magnitude in cell volume. The extracellular release of OC in our cultures represented on average similar to 2% of total carbon fixation, was not statistically different between growth stages, and was not correlated to cell size. The cell-specific OC exudation rate held an isometric relationship with cell size during the different growth phases (average slope: 0.95), which implies that general allometric models cannot be used to predict exudation in marine phytoplankton.