© 2001 Heron Publishing—Victoria, Canada
Mechanisms of xylem recovery from winter embolism in Fagus sylvatica
Hervé Cochard (1), Damien Lemoine (2), Thierry Améglio (1) and André Granier (2)
1. UMR-PIAF, INRA-UBP, Site de Crouël, 63039 Clermont-Ferrand, France / 2. UA Ecophysiologie Forestière, INRA, 54280 Champenoux, France / Received February 21, 2000
Summary
Hydraulic conductivity in the terminal branches of mature beech trees (Fagus sylvatica L.) decreased progressively during winter and recovered in the spring. The objective of this study was to determine the mechanisms
involved in recovery. Two periods of recovery were identified. The first recovery of hydraulic conductivity occurred early
in the spring, before bud break, and was correlated with the occurrence of positive xylem pressure at the base of the tree
trunk. Active refilling of the embolized vessels caused the recovery. The second recovery of hydraulic conductivity occurred
after bud break and was correlated with the onset of cambial activity. Formation of new functional vessels, leading to an
increase in xylem diameter, was largely responsible for the increase in xylem conductivity. The two mechanisms were complementary:
active refilling of embolized vessels occurred mostly in the root and the trunk, whereas formation of new functional vessels
occurred mainly in young terminal shoots.
Keywords:
beech, cavitation, growth, hydraulic conductance, root pressure, water relations.
