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Eucalypt saplings in north Australian savannas commonly die back, sometimes to ground level, during the 5 months of the long dry season. Water potentials are lower in saplings than large trees during the dry season, and we hypothesized that low water potentials may lead to high levels of xylem embolism and consequent death of branches and whole shoots. As the dry season progressed, hydraulic conductance of terminal branches decreased by 50% in Eucalyptus tetrodonta but not in Eucalyptus miniata saplings. Hydraulic conductance per leaf area decreased seasonally by 34% in E. tetrodonta branches. These decreases may be associated with the loss of leaves recorded from E. tetrodonta but not E. miniata branches. We modelled the effect of sequential loss of parallel resistors, representing petioles on a branch. This showed there is a non-linear decrease in flow as basal resistors are lost, which can lead to a decrease in mean flow per resistor due to increased mean path-length. Thus the observed loss of basal leaves, together with xylem embolism, probably contributed to the seasonal loss of hydraulic conductance in E. tetrodonta saplings. Loss of hydraulic conductance due to xylem embolism was generally low (< 15%) in both species, and the seasonal increase in embolism could not fully account for the decline in hydraulic conductance of E. tetrodonta branches. There was little evidence that branch and shoot death was caused by these levels of embolism. Developing an embolism vulnerability curve for species with long vessels is problematic and this issue is discussed.

Item Type:	Refereed Article
Keywords:	Eucalyptus;drought stress;evergreen;path-length;tropics;vulnerability curve;water potential
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Physiology
Objective Division:	Environment
Objective Group:	Flora, Fauna and Biodiversity
Objective Field:	Flora, Fauna and Biodiversity at Regional or Larger Scales
UTAS Author:	Prior, LD (Dr Lynda Prior)
ID Code:	72710
Year Published:	2000
Web of Science® Times Cited:	37
Deposited By:	Research Division
Deposited On:	2011-08-30
Last Modified:	2011-09-29
Downloads:	2 View Download Statistics