Question

7. (10) The total CO2 (TCO,) concentration of seawater is roughly 2,300 umoles/L; you will recall that TCO2 includes the sum of carbonate (CO3), bicarbonate (HC03) and carbon dioxide (CO2). At normal ocean pH (roughly pH 8) bicarbonate is the most abundant inorganic carbon species and carbon dioxide (CO2 per se) is present at a concentration of roughly 15 umoles/L Typical deep water nitrate and phosphate concentrations are 40 and 3 umoles/L, respectively. Is dissolved inorganic carbon a limiting resource in phytoplankton production? Elaborate using logic we've discussed in class, e.g., Redfield ratios (C:N:P; 106:16:). Please include the following two potential scenarios in your analysis 1) phytoplankton can utilize any of the 3 forms (species) of inorganic carbon listed above or 2) phytoplankton can only utilize carbon dioxide (CO2) per se

Answer 1

Research has shown that HCO3- is the principal form of inorganic carbon taken up by most phytoplanktons. In cyanobacteria HCO3- is absorbed directly through transmembrane transport diffusion. Diatoms express extracellular carbonic anhydrase and transported CO2 derived from the catalyzed dehydration of HCO3-.

However, inorganic carbon is not believed to limit the rate of short term photosynthesis, the net productivity or the maximum biomass of marine phytoplankton. The main factors which limit productivity are limited light, nitrogen and phosphorus supply in the water.