Gas Exchange of Algae: I. Effects of Time, Light Intensity, and Spectral-Energy Distribution on the Photosynthetic Quotient of Chlorella pyrenoidosa

Continuously growing cultures of Chlorella pyrenoidosa Starr 252, operating at constant density and under constant environmental conditions, produced uniform photosynthetic quotient (PQ = CO₂/O₂) and O₂ values during 6 months of observations. The PQ for the entire study was 0.90 ± 0.024. The PQ remained constant over a threefold light-intensity change and a threefold change in O₂ production (0.90 ± 0.019). At low light intensities, when the rate of respiration approached the rate of photosynthesis, the PQ became extremely variable. Six lamps of widely different spectral-energy distribution produced no significant change in the PQ (0.90 ± 0.025). Oxygen production was directly related to the number of quanta available, irrespective of spectral-energy distribution. Such dependability in producing uniform PQ and O₂ values warrants a consideration of algae to maintain a constant gas environment for submarine or spaceship use.