Respiration losses in planktonic green algae cultivated in raceway ponds

Rates of respiratory oxygen uptake were measured in darkenedsamples of green microalgae (Coelastrum sphaericum, Scenedesmusfalcatus) growing in raceway ponds under field conditions andindoors. The rates measured over 6–26h varied between1 and 1.5 and 8.25 µl O₂ mg^–1 h^–1 and dependedon incubation, temperature, time in the dark, and on the temperatureand irradiance at which the algae were cultivated before. Q₁₀values ranged from 1.43 to 1.68. Arrhenius relationships describedthe influence of temperature upon respiration rates below theoptimum temperature, even after many hours of incubation inthe dark. Respiration rates were lower after growth at optimaltemperature than after cultivation at other temperatures. Thelight history also influenced the rates, being high when thealgae were darkened after exposure to high irradiance and lowerafter weaker pre-illumination. For the algae under study theoverall loss during 12h of darkness was estimated to be 2–10%of the biomass prior to darkening. Higher losses are expectedfor natural conditions and stronger irradiances.