Photosynthesis and Photorespiration in Algae

Abstract

The CO2 exchange of several species of fresh water and marine algae was measured in the laboratory to determine whether photorespiration occurs in these organisms. The algae were positioned as thin layers on filter paper and the CO2 exchange determined in an open gas exchange system. In either 21 or 1% O2 there was little difference between 14CO2 and 12CO2 uptake. Apparent photosynthesis was the same in 2, 21, or 50% O2. The compensation points of all algae were less than 10 μl 1−1. CO2 or 14CO2 evolution into CO2-free air in the light was always less than the corresponding evolution in darkness. These observations are inconsistent with the proposal that photorespiration exists in these algae.