Effects of water deficits on 13C discrimination and transpiration efficiency of Eucalyptus globulus clones

Abstract

Potted cuttings of three Eucalyptus globulus Labill. clones (AR3, CN44, MP11) were grown over 6 months in a greenhouse under three watering regimes: well watered (HW), moderate soil water deficit (MS) and severe soil water deficit (SS). Transpiration efficiency (W = total dry matter/water transpired) and leaf intrinsic gas exchange efficiency (A/g_s = carbon assimilation rate/stomatal conductance) increased under water stress and were positively correlated with the stable carbon isotope composition of leaf tissue (δ¹³C). The clones did not vary significantly with respect to A/g_s and W. However, statistically significant differences were detected among clones in δ¹³C, A and biomass. W did not differ between the MS and SS regimes, probably due to plant acclimation to increasing soil water deficits. The increase in W with soil water deficits relative to the well watered control was primarily associated with stomatal closure, but was also influenced by differences in respiratory carbon losses (&phis;_c) and variation in the leaf-to-air water vapour difference (v). Variance in &phis;_c and v may explain partially why the two levels of soil water deficit were different in regard to δ¹³C but not in terms of W.