The Partitioning of Resistances to Gaseous Diffusion in the Leaf Epidermis and the Boundary Layer

The partitioning of total leaf resistance to gaseous diffusion into the cuticular, stomatal, and boundary-layer components of the upper and lower leaf surfaces was studied. A general formula was developed, which showed that the mean stomatal or even mean epidermal resistances may not be obtained by simple subtraction of the boundary-layer component from the total, except in very specific cases. The formula was used to study the relationship between the mean stomatal resistance, $r¯$_s, and the residual leaf resistance, r_l (obtained by subtracting the boundary-layer from the total resistance), in leaves differing in their degree of anisolaterality (with respect to stomatal resistance), cuticular resistance, and total resistance, as affected by the relative magnitude of the boundary-layer component. Graphical presentation of the analyses permits evaluation of the difference between $r¯$_s, and r_l in a wide variety of cases. It was shown experimentally that when the stomatal component of each leaf surface is known, the total resistance calculated from these values according to the formula closely matches the measured value.