Photosynthetic acclimation to elevated atmospheric CO₂ concentration in the Florida scrub-oak species Quercus geminata and Quercus myrtifolia growing in their native environment

Long-term effects of elevated CO₂ concentration (ambient plus 350 μmol mol^-1) on leaf photosynthetic acclimation of two species of a scrub-oak community, Quercus myrtifolia Willd. and Quercus geminata Small, were studied. Plants of both species were grown in open-top chambers in their natural habitat at Kennedy Space Center, Florida, USA. Compared to ambient CO₂, elevated CO₂ stimulated photosynthetic rates by 73 and 51% for Q. geminata and Q. myrtifolia, respectively. Maximum rate of carboxylation (V(cmax)) was significantly reduced by elevated CO₂ in Q. myrtifolia (28%) but not in Q. geminata. Maximum rate of potential electron transport (J(max)) was not significantly reduced by elevated CO₂ in either species. In response to elevated CO₂, specific leaf area decreased in Q. myrtifolia (22%), but not in Q. geminata. Elevated CO₂ caused a significant accumulation of sugars (54%) and starch (264%) in Q. myrtifolia leaves, but not in Q. geminata leaves. Total Rubisco activity in Q. myrtifolia leaves was reduced 40% by elevated CO₂, whereas no significant reduction occurred in Q. geminata leaves. Although both species share a common habitat, they exhibited marked differences in photosynthetic acclimation to elevated CO₂ concentration.