Stomatal adaptation of grapevine leaves to water stress
AbstractStomata of grapevine leaves respond to the evaporative demand of the atmosphere and to changes of soil water. Leaf epidermis and roots are regarded as sensors of air and soil humidity. Besides a hydraulic communication between soil and leaf, non-hydraulic signals represent a metabolic communication between roots and stomata: stomatal conductance, and thereby the rate of CO2 assimilation, of turgid vine leaves declined when part of the roots was subjected to progressively drying soiL
Under water stress conditions stomata of leaves reduce transpiration and fully account for putative non-stomatal inhibition of CO2 assimilation. They enable vine leaves to optimize their CO2 uptake to water loss ratio (water use efficieny) under sometimes rapidly changing ambient and internal conditions. A close correlation between CO2 assimilation and stomatal conductance indicates a precise functioning of stomatal action and thereby a high water use efficiency; this correlation coefficient which is generally high in grapevines was demonstrated to increase under water stress conditions. As a screening, the CO2 assimilation to stomatal conductance ratio and the CO2 assimilation to transpiration ratio provide valuable information on the water economy of grapevine varieties under drought conditions.
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