Response to Saturation Deficit of Leaf Extension in a Stand of Pearl Millet (Pennisetum typhoidesS. & H.)II

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Abstract
This paper describes how the dominant relation between leaf extension and temperature in pearl millet is modified by atmospheric saturation vapour pressure deficit (SD) and irradiance. Stands of plants were grown at two levels of SD and soil moisture content. Leaf extension, water potential (Ψ1) and stomatal conductance were all reduced at high SD, Ψ1 was more closely related to transpiration rate than to SD itself. Leaf extension rate (R) was poorly correlated with Ψ1, even after correction for temperature differences, owing to variation in solute potential between leaves. However, R in individual leaves was linearly related to turgor potential, except after periods of low irradiance. The thermal time concept was modified to incorporate turgor potential and used to show that the ‘turgor thermal rate of extension’ decreased sharply at low irradiances, presumably due to assimilate shortage.