Stomatal conductance correlates with photosynthetic capacity

Abstract

Previous studies on the Physiology of stomata in higher plants suggest that stomata influence the rate of CO₂ 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 CO₂ 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 CO₂. Thus, the intercellular concentration of CO₂ (c_i), calculated as c_i = c_a–A/g (where c_a is ambient concentration of CO₂, A is assimilation rate of CO₂), tends to remain constant providing ca is kept constant. We used routine techniques¹ to measure A and estimate g in leaves placed singly in chambers. Conductance takes account of CO₂ transfer through both stomata and leaf boundary layer, the conductance of the latter being 0.5 mol m⁻² s⁻¹.