Effects of Intercellular Resistances on Estimates of the Intracellular Resistance to Co2 Uptake by Plant Leaves

Abstract

A model is presented for net CO2 uptake by plant leaves, which is particularly relevant to those leaves having different upper and lower stomatal resistances. The model includes intercellular space resistances to CO2 uptake via both the upper and lower surfaces. Experimental data obtained with Pelargonium hortorum Bailey show that the ratio of the rates of C02 exchange through the lower and upper surfaces respectively is in all cases greater than the ratio of the corresponding rates of water vapour exchange. This provides evidence for a substantial vapour phase resistance to C02 uptake via the upper epidermis, which is not accounted for by the usual water vapour analogue. The data also suggest that calculations of intracellular resistance r'i, using conventional resistance models, may be subject to error. How-ever, the magnitude of the error in estimates of the intracellular resistance is seldom likely to exceed 10%, so that for most purposes changes in the conventional models do not appear to be warranted.