The effect of night temperature on Co2 assimilation, transpiration, and water use efficiency in agave americana l

Abstract

The CO2 and water vapour fluxes arising from the tops of a plant of A. americana, growing in nutrient solution, were continuously measured at night temperatures of 15, 25, and 36°C, the day temperature being held constant at 25°C Night temperatures of 36°C inhibited both the large nocturnal uptake of CO2 and the accumulation of titratable acidity. The highest rate of CO2 assimilation by day was about half that of the maximum rate observed by night. From the observed rhythms in transpiration rate, it was inferred that high night temperatures also reversed the usual "inverted" stomatal rhythm found in A. americana and other crassulacean plants. Relative to measurements made at a low night temperature (15°C), high night temperatures induced greater stomatal closure at night and opening during the day. The changes in the gas-exchange pattern induced by high night temperature caused the water use efficiency of this plant to fall to values normally associated with noncrassulacean plants. It is concluded that the normal high water use efficiency of A. americana, and its consequent adaptation to arid climates, is causally associated with a requirement for low night temperatures. © 1973, CSIRO. All rights reserved.