Photosynthesis and light and dark respiration in freshwater algae

Rates of gas exchange were measured for cultures of Chlorella pyrenoidosa, Chlamydomonas reinhardtii, and Anabaena flos-aquae, which were suspended in moist air on an artificial leaf made with nylon bolting cloth. A 14 CO 2 – 12 CO 2 technique was used to measure net and gross photosynthesis and light and dark respiration in air or nitrogen. Rates of gas exchange on the artificial leaf were equal to maximum rates obtainable for the same algae suspended in culture medium. Rates were stable, and the artificial leaf could be maintained for many hours.The algae did not exhibit conventional photorespiration. However, they did have a variable rate of light respiration that frequently equalled, but did not exceed, the rate of dark respiration. This light respiration appeared to be a continuation of normal dark respiration in light. It was affected by CO 2 concentration, declining to zero if the cells were illuminated in the absence of CO 2 . Unlike higher plants, recent photosynthate is not a substrate of light respiration in these algae.