Stomatal conductance and root conductivity have been considered the main controlling factors of water flow in the plant. However, structure and efficiency of the xylem transport system can affect water movement. If exposed to water stress, plants reduce water flow rate decreasing the conductivity components of the transpiration pathway. The objective of this work was to investigate on the relative importance of hydraulic canopy conductivity versus stomatal conductance on the control of water losses by transpiration under water stress conditions. Water stress of different intensity and duration were imposed to potted vines either with root system in one pot or divided in two (twin-root) in order to modify water stress signals to the stomata independently to hydraulic condition. Shading treatments to the leaves were imposed to induce stomatal closure, independently to water stress. Stomatal conductance and leaf transpiration were assessed by gas exchange measurements. Hydraulic conductivity was checked in vivo by calculation of the ratio between water flow along the shoot and the relative shoot water potential (measured by pressure chamber on bagged leaves). Moreover, hydraulic conductivity was assessed at the end of the growing season by direct measurements on excised shoot (measured by forced pressured water in the xylem), assessing embolization percentage in treatments. Changes in water availability affected both stomatal conductance and hydraulic conductivity. As xylem hydraulic conductivity decreased, stomatal conductance was initially linearly correlated with conductivity. However excessive decrease of hydraulic conductivity was avoided by stomatal closure. A nonhydraulic signal was hypothesized, and interrelationships between conductivities were determined dependently to the different intensities and durations of imposed stress. Effects of the changes in xylem conductivity and stomatal closure induced by water stress are evaluated not only for reducing water loss from the plant, but also because of their relative importance for avoiding embolization.
Interrelationship between stomatal conductance and xylem hydraulic conductivity on transpiration control in water stressed grapevines.
LOVISOLO, Claudio;SCHUBERT, Andrea
2000-01-01
Abstract
Stomatal conductance and root conductivity have been considered the main controlling factors of water flow in the plant. However, structure and efficiency of the xylem transport system can affect water movement. If exposed to water stress, plants reduce water flow rate decreasing the conductivity components of the transpiration pathway. The objective of this work was to investigate on the relative importance of hydraulic canopy conductivity versus stomatal conductance on the control of water losses by transpiration under water stress conditions. Water stress of different intensity and duration were imposed to potted vines either with root system in one pot or divided in two (twin-root) in order to modify water stress signals to the stomata independently to hydraulic condition. Shading treatments to the leaves were imposed to induce stomatal closure, independently to water stress. Stomatal conductance and leaf transpiration were assessed by gas exchange measurements. Hydraulic conductivity was checked in vivo by calculation of the ratio between water flow along the shoot and the relative shoot water potential (measured by pressure chamber on bagged leaves). Moreover, hydraulic conductivity was assessed at the end of the growing season by direct measurements on excised shoot (measured by forced pressured water in the xylem), assessing embolization percentage in treatments. Changes in water availability affected both stomatal conductance and hydraulic conductivity. As xylem hydraulic conductivity decreased, stomatal conductance was initially linearly correlated with conductivity. However excessive decrease of hydraulic conductivity was avoided by stomatal closure. A nonhydraulic signal was hypothesized, and interrelationships between conductivities were determined dependently to the different intensities and durations of imposed stress. Effects of the changes in xylem conductivity and stomatal closure induced by water stress are evaluated not only for reducing water loss from the plant, but also because of their relative importance for avoiding embolization.
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