Der Diffusionswiderstand der Spaltöffnungen; ein Vergleich des CO₂-Gaswechsels von Blättern mit und ohne Epidermis

Summary

The lower epidermis from leaves of Primula palinuri can be stripped off. Light-saturation curves of the CO₂-exchange were measured at 20°C and 300 ppm CO₂. Whereas the normal leaf reaches light-saturation at 0.3 cal cm^-2 min^-1, even 0.6 cal cm^-2 min^-1 is not sufficient to saturate the stripped leaf. Transpiration, apparent CO₂-uptake and leaf-temperature were measured simultaneously. The data were used to calculate the diffusion resistances for CO₂ with the usual methods, that is, from the diffusion resistances for water-vapour transport. The comparison of the CO₂-exchange of stripped and normal leaves makes it possible to determine the resistances—in particular those of the stomata—directly from the CO₂-exchange. Both methods agree well. When CO₂ exchanges only through the lower surface of the leaf the epidermis is—even with opened stomata—a considerable diffusion resistance. It lowers the CO₂-concentration in the intercellular system to 160 ppm and limits the CO₂-uptake.