The Relation between Photosynthesis and Stomatal Resistance of Each Leaf Surface in Cotton Leaves

Abstract

AbstractThe relation between photosynthesis and stomatal resistance of each leaf surface in cotton leaves (Gossypium hirsutum) was studied during ageing and with increase in light intensity.During ageing of leaves the stomatal resistance of the upper surface increases before that of the lower surface. This observation would suggest that the stomata of the upper leaf surface commence to age before those of the lower leaf surface. The earlier commencement of the increase in upper stomatal resistance results in the decline in photosynthesis at an early stage of ageing being negatively correlated with the upper stomatal resistance and not related to the lower stomatal resistance. The results indicate that in this initial phase of ageing the decrease in photosynthesis and increase in stomatal resistance of the upper surface are not causally related but occur simultaneously. At a more advanced stage of ageing the lower stomatal resistance also increases and then the decline in photosynthesis becomes related to the increase in stomatal resistance of both leaf surfaces.When illumination of leaves is increased stepwise, the resultant increase in photosynthesis is related to the reduction in stomatal resistance of each leaf surface. At low light intensities the stomatal resistance of the lower surface is low while that of the upper surface is relatively high. The difference between them decreases with increase in light intensity. This would indicate that the upper stomata require a higher light intensity to open than the lower stomata.The stormatal resistance of the two leaf surfaces is not related to the stomatal frequencey.