Antitranspirant Action of Carbon Dioxide on Intact Sorghum Plants

Twenty‐day‐old hybrid sorghum ( Sorghum bicolor (L.) Moench) plants of the ‘Oro’ variety were grown in a closely controlled environment in which the air temperature was 30 C, the humidity about 80%, the horizontal air flow about 1 m s −1 , and the incident, photosynthetically active radiation close to the maximum daylight level in clear weather. The ambient carbon dioxide level was varied to induce varying degrees of stomatal aperture and internal levels of carbon dioxide. This manipulation affected transpiration and carbon assimilation simultaneously, decreasing the former and increasing the latter. The results were compared with a mathematical model of leaf action in which assumptions had to be made as to the mathematical form of the relations and the value of the constants. The effect of the carbon dioxide level upon stomatal aperture was well predicted by the model, as originally conceived, regarding both the nature of the functional relation and the value of the constant required.