Fig. 4. Population density, inorganic carbon chemistry, and pH in chemostat experiments with Microcystis PCC 7806 at low and at high pCO₂.

Chemostat experiments were performed in duplicate, at low pCO₂ (left) and at high pCO₂ (right). (A and B) Microcystis population density (n = 3 technical replicates per chemostat) and light intensity I_out transmitted through the chemostat (n = 10). (C and D) Dissolved CO₂, bicarbonate, and carbonate concentrations. (E and F) Dissolved inorganic carbon (DIC) and pH (n = 3 technical replicates per chemostat). Symbols indicate experimental data of the duplicate chemostat experiments, error bars indicate SDs of technical replicates, and lines indicate model predictions. Error bars in (E) and (F) did not exceed the size of the symbols. For comparison, gray lines in (A) and (B) are model predictions for nonacclimated cells that either (A) grow at low pCO₂ but with carbon uptake kinetics acclimated to high pCO₂ or (B) grow at high pCO₂ but with carbon uptake kinetics acclimated low pCO₂. Steady-state characteristics of the experiments are summarized in table S1, and parameter values of the model are listed in tables S4 and S5.