Variation in Drought Tolerance in Eucalyptus viminalis Labill

Abstract

Six-month-old seedlings of two low rainfall populations of Eucalyptus viminalis showed greater resistance to desiccation and were less damaged by sustained drought than seedlings from two high rainfall populations. The more resistant seedlings did not simply avoid drought by quickly closing stomata, but were capable of maintaining relatively high rates of transpiration under moderate moisture stress. The two populations from moist habitats wilted at a higher relative turgidity of leaves than did the populations from the drier habitats. Furthermore, for populations from one dry habitat and one moist habitat, changes in relative turgidity in relation to water potential of leaves during drying were not significantly different. It is suggested that the greater tolerance of the low rainfall populations to drought is related to physiological resistance of the protoplasm to desiccation. Some differences in drought resistance were also noted between the two low rainfall populations. Young seedlings (3 months old) from a population on a deep basalt-derived soil were less resistant than young seedlings from a neighbouring population on a shallower granite soil. It is suggested that the selection for drought tolerance at the granite site has been more severe than at the basalt site.