The lower epidermis from leaves ofPrimula palinurican 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-2min-1, even 0.6 cal cm-2min-1is 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 CO2with 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 CO2exchanges 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 CO
展开▼
