Plant Water Status and Carbon Dioxide Exchange of Cotton Leaves

Abstract

The effect of plant water status on the diffusion of C02 in the gas and liquid phase in leaves of cotton plants was studied in a single leaf chamber under conditions of constant light level and temperature and when photosynthesis was limited by the CO2 supply. A controlled range of relative leaf water contents from 56 to 96% was obtained by varying root temperature from 6 to 30°C while the tops of the plants were -at a constant temperature. Decreasing water content resulted in an increase in the calculated leaf diffusive resistance and a decrease in CO2 exchange. Under the environmental conditions used, plant water status primarily affects C02 exchange by regulating stomatal aperture. The mesophyll resistance, which was estimated in air and in an oxygen-free atmosphere, did not vary with the relative leaf water content down to 75% but increased progressively as relative water content dropped from 75 to 56%.