[The diffusion resistance of stomata: a comparison between the CO2-exchange of normal and stripped leaves]

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.