Water Relations of Eucalyptus Marginata Sm. Under Natural Conditions

Abstract

The eco-physiology of E. marginata in spring and mid-summer was studied, to investigate the development of water stress in the tree. In spring, when the surface soil water content was high, the course of transpiration followed that of evaporation. By mid-summer the surface soil water content was low, evaporation rate was high, and a midday depression of transpiration occurred in association with partial closure of the stomata. Young leaves transpired approximately 20% less than mature leaves on a sunny day, as a result of more effective stomatal closure. Leaf water deficits reached the same minimum values during mid-summer as in early spring, indicating the existence and utilization of water from deeper layers in the soil. Sap flux was linearly related to leaf water deficit, and the pattern of the relationship during any day was interpreted to indicate the extent of water reserves within the plant. The water deficits which develop in E. marginata under the conditions of the investigation are probably due to factors of the climate and of redistribution of water within the plant, rather than to restriction of the water supply from the soil.