Changes in Water Relations of Cornus stolonifera During Cold Acclimation1

Abstract

Abstract Stomatal resistance of leaves, water absorption through roots, and water content of stem internodes was evaluated during cold acclimation of red-osier dogwood (Cornus stolonifera Michx.). Four weeks of short-days at 20/15°C resulted in a significant reduction in stem water content. This reduction was related to water lost from pith cells as this tissue senesced sequentially in successively younger internodes from the stem base to its apex at autumn growth cessation. A 1.5 fold decrease in relative stomatal resistance of leaves and a 3.5 fold increase in resistance to water flow though roots at 0.15 bars tension occurred prior to hardening to -12°C. Additional hardening to -40°C resulted in a 28 fold increase in resistance to forced water flow through roots and equalization of water content in all internodes. Thereafter, water content remained constant but stems continued to harden to temperatures below -65°C. Comparison of resistance to forced water flow through living and dead roots from hardy and tender plants suggested there was a decrease in the permeability of root cells to water during the initial (-12°C) stage of acclimation. Root surfaces became suberized, as acclimation progressed, giving rise to an additional barrier to water uptake in roots of very hardy plants (-45°C). It seems likely that the decrease in hydration of overwintering stems during cold acclimation results from a decreased stomatal resistance and increased root resistance to water movement.