A METHOD FOR SEPARATING CUTICULAR AND STOMATAL COMPONENTS OF GAS-EXCHANGE BY AMPHISTOMATOUS LEAVES .1. MODEL SOLUTION

A new technique for estimating the cuticular component of epidermal gas exchange by a stomatous leaf side is proposed. It is based on the process of elimination of stomatal diffusion by mass (viscous) flow of air applying an air pressure gradient across the leaf. This technique was designed to enable a reliable estimation of the cuticular component irrespective of stomatal opening.A model solution of diffusive and mass flow counteraction in terms of general substance fluxes is presented. Water vapour loss and CO2 uptake by a model leaf was simulated by varying both stomatal diffusion resistance and viscous flow of air through the stomatal pores in physiologically and experimentally relevant ranges. Depending on stomatal opening, elimination of the stomatal contribution to epidermal vapour and CO2 exchange by the viscous flow of air ranged from small to practically complete. It supports the relevance of the procedure for cuticular vapour loss estimation under conditions of partially open stomata.Modification of the model CO2-uptake patterns due to expected changes in intercellular CO2 concentration, coc, was evaluated. Net CO2 flux under the diffusive-viscous flows counteraction is sensitive to the changes mentioned above. Nevertheless, the changes in coc, evaluated by a simple model, were too small to cause significant departures from the CO2-uptake elimination curves by constant coc. The relevance of the method for the determination of cuticular CO2-uptake is discussed. © 1990 Oxford University Press.