Fig. 2

Quantum absorption rates Q_phar (a) and effective quantum yields at PSII Y(PSII) (b) under different steady state conditions. PCC6803 was grown with ammonium (striped bars) or nitrate (white bars) as N source under LLHC (low light high carbon), HLHC (high light high carbon), and HLLC (high light low carbon) conditions. Cells were cultivated in a bioreactor setup in a continuous (turbidostat) mode to achieve stable steady metabolic states. Light and carbon supply were varied to force the cells into different sink–source balances. The light intensity was set to either 65 (LL) or 250 (HL) µmol photons m⁻² s⁻¹, and carbon was supplied with ambient CO₂ concentration in air (LC) or air enriched with 1% CO₂ (HC). Mean values and standard deviations were calculated for three different measurement days. See “Materials and methods” for details on the measurements