EFFECTS OF ATMOSPHERIC SATURATION DEFICIT ON THE STOMATAL CONDUCTANCE OF PEARL-MILLET (PENNISETUM-TYPHOIDES S AND PENNISETUM-TYPHOIDES H) AND GROUNDNUT (ARACHIS-HYPOGAEA L)

Experiments were carried out to investigate the influence of atmospheric saturation deficit on the stomatal conductances of millet and groundnut plants grown in undisturbed soil in controlled environment glasshouses. Environmental conditions during growth were maintained close to those experienced in the semi-arid tropics.The results demonstrated that the stomatal conductances of well-watered plants of both species were affected strongly by changes in saturation deficit. The response was stronger at higher irradiances when variations in saturation deficit between 1.5 and 3.0 kPa caused 3-4-fold changes in leaf conductance. However, the stomatal response was greatly reduced or absent in unirrigated plants in which stomatal conductances were reduced.Reduction of the transpiring leaf area by covering some of the leaves increased the leaf conductances of the remaining leaves and partially restored the stomatal response to saturation deficit in unirrigated plants. Leaf conductance was sensitive to the transpiring area per plant and declined as the transpiring area increased. However, the reduction in mean leaf conductance was insufficient to prevent an increase in canopy conductance owing to the increased transpiring area:. The results are compared to earlier field data for millet, and the possible origin of the stomatal response is discussed. © 1979 Oxford University Press.