© 1990 Heron Publishing—Victoria, Canada
Xylem dysfunction in Quercus: vessel sizes, tyloses, cavitation and seasonal changes in embolism
Hervé Cochard (1) and Melvin T. Tyree (2)
1. Station de Syvliculture et de Production, INRA, Centre de Recherches Forestières de Nancy, Champenoux 54280 Seichamps, France / 2. Northeastern Forest Experiment Station, P.O. Box 968, Burlington, Vermont 05402, USA / Received January 16, 1990
Summary
The seasonal progression of xylem dysfunction from tyloses and embolism induced both by cavitation and frost was studied in
Quercus rubra L. and Quercus alba L. branches. Vessel lengths and diameters were measured in current-year rings of branches of various ages. Vessels in current-year
shoots are about the same size as those in many diffuse porous trees, but vessels in older branches are two to six times larger
in diameter and typically more than 10 times longer. Large Quercus vessels were more vulnerable to cavitation than small vessels. The small vessels in current-year shoots were more vulnerable
to cavitation than vessels of comparable size in diffuse porous species. Earlywood vessels are completely blocked by tyloses
within a year of their formation. Tylose growth starts in winter, but the vessels are not fully blocked until the next summer.
Many latewood vessels, by contrast, remain free of complete blockage for several years. In Q. rubra, loss of hydraulic conductivity in current-year shoots due to cavitation reaches 20% by August and > 90% after the first
hard frost. Both laboratory and field observations confirm that the role of frost in causing loss of hydraulic conduction
by embolism is much more dramatic in Quercus than in conifers and diffuse porous hardwoods.
