Is Transfer of CO2 to C3-Plants Purely by Diffusion?

The dependence of the CO 2 compensation concentration on O 2 partial pressure and the dependence of differential uptake of 14 CO 2 and 12 CO 2 on CO 2 and O 2 partial pressures are analyzed in illuminated white clover ( Trifolium repens L.) leaves. The data show a deviation of the photosynthetic gas exchange from ribulose bisphosphate carboxylase oxygenase kinetics at 10°C but not at 30°C. This deviation is due to an effect of CO 2 partial pressure on the ratio of photosynthesis to photorespiration which can be explained if active inorganic carbon transport is assumed.