Figure 1.

Rates of photosynthesis (P), CO₂ uptake or efflux (Cup), and HCO₃⁻ uptake (Bup) in Prochlorococcus spp. MED4 as a function of C_i concentration for cells grown at 150 µL L⁻¹ CO₂ (A) and 1,000 µL L⁻¹ CO₂ (B). Positive rates indicate uptake into the cell, and negative rates indicate efflux from the cell. C_i concentrations in the culture medium were approximately 1,850 μm at 150 µL L⁻¹ CO₂ and approximately 2,200 μm at 1,000 µL L⁻¹ CO₂.