Calculation of Leaf Photosynthetic Parameters Considering the Statistical Distribution of Stomatal Apertures

It was shown earlier (Laisk, Oja, and Kull, 1980) that different stomata on a barley leaf are open to different degrees. Therefore, stomatal conductance is a quantity which is statistically distributed over a large range in the geometry of one leaf. Gas exchange measurements based on transpiration rates represent the average value of stomatal conductance in the leaf chamber. The conventional method of calculating mesophyll resistance involves subtracting stomatal resistance from total leaf resistance. It is incorrect, however, to average the stomatal resistance before this subtraction. Therefore, the conventional method for calculating the mesophyll resistance contains an error as it neglects the statistical distribution of stomatal apertures. The error is significant when the diffusion resistance between neighbouring substomatal cavities is large and when stomatal apertures vary over a wide range.