Drought-induced leaf shedding in walnut: evidence for vulnerability segmentation


Melvin T. Tyree, U.S. Forest Service, PO Box 968, Burlington, VT 05402, USA.


Trees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87% of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water-stress induced cavitation. These data are discussed in the context of the plant segmentation hypothesis.