Stomatal conductance correlates with photosynthetic capacity

Previous studies on the Physiology of stomata in higher plants suggest that stomata influence the rate of CO 2 fixation in leaf mesophyll tissue. We believe that an equally important stomatal function has not been fully recognised; that stomatal aperture is determined by the capacity of the mesophyll tissue to fix carbon. We altered the capacity of leaves to fix carbon by various means, and found invariably that the diffusive conductance of the epidermis to CO 2 transfer, g , (which mainly depends on the number and dimensions of the stomata) changes in nearly the same proportion as the rate of assimilation of CO 2 . Thus, the intercellular concentration of CO 2 ( c i ), calculated as c i = c a –A/g (where c a is ambient concentration of CO 2 , A is assimilation rate of CO 2 ), tends to remain constant providing ca is kept constant. We used routine techniques 1 to measure A and estimate g in leaves placed singly in chambers. Conductance takes account of CO 2 transfer through both stomata and leaf boundary layer, the conductance of the latter being 0.5 mol m −2 s −1 .