Quantum yields for CO₂ uptake in some diploid and tetraploid plant species

Quantum (photon) yields for CO 2 uptake on an absorbed photon fluence rate (PFR) basis (φ a ) were determined for a number of diploid and tetraploid species under a range of experimental conditions. Little variation in φ a was found either between species or across ploidy levels, which suggests that there are no intrinsic differences in the kinetics of CO 2 fixation. Variations in photosynthetic rate or quantum yield expressed on an incident PFR basis (φ j ) were found to be largely due to differences in leaf absorptance. On this basis these results do not support the biochemical evidence showing ploidy‐related differences in the K m (CO 2 ) of ribulose ‐1,5‐bisphosphate carboxylase/oxygenase. However, there are obvious difficulties in relating in vitro enzyme kinetic data to in vivo studies and these problems are discussed.