PHOTOSYNTHETIC ACCLIMATION IN TREES TO RISING ATMOSPHERIC CO2 - A BROADER PERSPECTIVE

Analysis of leaf-level photosynthetic responses of 39 tree species gro wn in elevated concentrations of atmospheric CO2 indicated an average photosynthetic enhancement of 44% when measured at the growth [CO2]. W hen photosynthesis was measured at a common ambient [CO2], photosynthe sis of plants grown at elevated [CO2] was reduced, on average, 21% rel ative to ambient-grown trees, but variability was high. The evidence l inking photosynthetic acclimation in trees with changes at the biochem ical level is examined, along with anatomical and morphological change s in trees that impact leaf- and canopy-level photosynthetic response to CO2 enrichment. Nutrient limitations and variations in sink strengt h appear to influence photosynthetic acclimation, but the evidence in trees for one predominant factor controlling acclimation is lacking. R egardless of the mechanisms that underlie photosynthetic acclimation, it is doubtful that this response will be complete. A new focus on adj ustments to rising [CO2] at canopy, stand, and forest scales is needed to predict ecosystem response to a changing environment.