Effect of Oxygen on Photosynthesis, Photorespiration and Respiration in Detached Leaves. I. Soybean

Abstract

The effect of O2 on the CO2 exchange of detached soybean leaves was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems. The rate of apparent photosynthesis was inhibited by O2 while the steady rate of respiration after a few minutes in the dark was not affected. Part of the inhibition of apparent photosynthesis was shown to be a result of increased photo-respiration. This stimulation of photorespiration by O2 was manifested by an increase in the CO2, compensation point. The differential effects of O2 on dark respiration (no effect) and photorespiration (stimulation) indicated that these were 2 different processes. Moreover the extrapolation of the CO2, compensation point to zero at zero O2 indicated that dark respiration was suppressed in the light at least at zero O2 concentration.