Effect of Oxygen and Temperature on the Efficiency of Photosynthetic Carbon Assimilation in Two Microscopic Algae

Abstract

The CO₂ compensation points of Coccochloris peniocystis, a blue-green alga and Chlamydomonas reinhardtii, a green alga, were determined at pH 8.0 in a closed system by a gas chromatographic technique. The compensation point of Chlamydomonas increased markedly with temperature, rising from 0.79 microliter per liter CO₂ at 15 C to 2.5 microliters per liter CO₂ at 35 C. In contrast, the compensation point of Coccochloris at 20 C was 0.71 microliter per liter CO₂ and rose to only 0.95 microliter per liter CO₂ at 40 C. The compensation point of the green alga was significantly reduced at low O₂ concentrations (1 to 2%) when measured over the temperature range of 15 to 35 C. The compensation point of the blue-green alga, over the temperature range of 20 to 40 C, was unaffected by lowering the O₂ concentration. The whole cell CO₂ affinity of Chlamydomonas decreased substantially with increasing temperature at 21% O₂ whereas little change was observed over the same temperature regime when the CO₂ affinity was determined at O₂ concentrations of 1 to 2%. The CO₂ affinity of Coccochloris did not decrease significantly with either increasing temperature or O₂ concentration. These results suggest that while photorespiration is undetectable in Coccochloris some photorespiratory CO₂ release occurs in Chlamydomonas.