Stomatal acclimation to increased CO₂ concentration in a Florida scrub oak species Quercus myrtifolia Willd

Native scrub‐oak communities in Florida were exposed for three seasons in open top chambers to present atmospheric [CO 2 ] (approx. 350 μmol mol − 1 ) and to high [CO 2 ] (increased by 350 μmol mol − 1 ). Stomatal and photosynthetic acclimation to high [CO 2 ] of the dominant species Quercus myrtifolia was examined by leaf gas exchange of excised shoots. Stomatal conductance ( g s ) was approximately 40% lower in the high‐ compared to low‐[CO 2 ]‐grown plants when measured at their respective growth concentrations. Reciprocal measurements of g s in both high‐ and low‐[CO 2 ]‐grown plants showed that there was negative acclimation in the high‐[CO 2 ]‐grown plants (9–16% reduction in g s when measured at 700 μmol mol − 1 ), but these were small compared to those for net CO 2 assimilation rate ( A , 21–36%). Stomatal acclimation was more clearly evident in the curve of stomatal response to intercellular [CO 2 ] ( c i ) which showed a reduction in stomatal sensitivity at low c i in the high‐[CO 2 ]‐grown plants. Stomatal density showed no change in response to growth in high growth [CO 2 ]. Long‐term stomatal and photosynthetic acclimation to growth in high [CO 2 ] did not markedly change the 2·5‐ to 3‐fold increase in gas‐exchange‐derived water use efficiency caused by high [CO 2 ].