Is Transfer of CO(2) to C(3)-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 degrees C but not at 30 degrees 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.