STOMATAL MOVEMENT AND PHOTOSYNTHESIS IN PELARGONIUM. I. EFFECTS OF LIGHT AND CARBON DIOXIDE

Abstract

The photosynthesis rate of single leaves in an air stream was measured at frequent intervals by means of an infra-red absorption method of estimating CO2. Simultaneously stomatal aperture of the same leaf was estimated, mainly by a modified porometer method. Red, green and white light at intensities that just cause photosynthesis to balance respiration produce the same stomatal opening at equilibrium. Opening in normal air seems to be better correlated with photosynthesis rate than light intensity. Reducing either the CO2 concn. or rate of flow of the air stream interacts with light intensity in regulating opening and, when the effect of stomatal aperture on the diffusion of CO2 is also taken into account, the degree of opening increases as the inferred concn. of CO2 within the leaf is reduced. The great inferiority of light opening in white as compared with green parts of a variegated leaf in normal air is largely overcome in CO2-free air, which in darkness produces the same opening in both regions. The results support the view that light acts on stomata largely by photosynthetic removal of CO2, but also indicate that the mechanism of the physiol. response must be complex.