Water Potential and Stomatal Conductance of Three Eucalyptus Species in the Mount Lofty Ranges, South Australia: Responses to Summer Drought

Abstract

Water potential and stomatal conductance were measured for three eucalypt species: Eucalyptus obliqua L'Hérit., E. fasciculosa F. Muell. and E. leucoxylon F. Muell. Field sites were located in the Mt Lofty Ranges, S.A., near the lower altitudinal limits of the E. obliqua population, where this species begins to be replaced by one or other of the other two. Pairs of trees, one pair of each species, were selected at each site growing within a few metres of each other. Measurements were made in late winter 1977 and during the unusually dry summer of 1977-78. In late winter E. obliqua and E. fasciculosa results were similar. Both had dawn water potential maxima of approximately -0.4 MPa, and stomatal conductance was high throughout the day. By mid summer E. obliqua was suffering water stress. Dawn water potential maxima of -1.93 and -4.35 MPa were measured, and stomatal conductance was low, but not zero, throughout the day. Adjacent E. fasciculosa showed few signs of stress; dawn maximum water potential was -0.7 MPa, and stornatal conductances were high. By late summer both water potentials and stornatal conductances of E. obliqua were much lower than those of adjacent trees of either of the other two species. The significance of these differences is discussed in relation to factors affecting eucalypt distribution patterns.