Inorganic carbon requirements of natural populations and laboratory cultures of some Chesapeake Bay phytoplankton

The rates of photosynthetic carbon fixation for some natural populations of Chesapeake Bay phytoplankton and for unialgal cultures of species isolated from those populations follow hyperbolic saturation kinetics with respect to total inorganic carbon concentrations. The apparent half-saturation constants, K_c, measured by ¹⁴C uptake are close to and in some cases larger than ambient concentrations of total inorganic carbon, indicating that inorganic carbon can be a limiting nutrient in eutrophic systems. Addition of bicarbonate ion to incubation bottles increased the measured ¹⁴C uptake rates by factors as high as 2.5 for natural samples and 4.5 for laboratory cultures.