Drought resistance and water use efficiency in Acacia saligna

Acacia saligna (Labill.) H.Wendl, a potential crop for forage and wood production, is considered highly drought-resistant. The aim of this study was to characterize some of the physiological traits contributing to drought resistance in A. saligna. Two experiments were conducted: (i) 4-year-old A. saligna were grown in the field under dryland and irrigated treatments and (ii) 6-month-old A. saligna were grown in pots and irrigated to replenish 100% of the transpiration demand (control), or 75% 50% or 25% of the control. Soil-water deficits in the field elicited an increase in osmotic potential in phyllodes. Stomatal conductance was negatively correlated with air vapor pressure deficit under drought conditions in both experiments, whereas under irrigation in the field it was correlated with solar radiation. In the field, dry matter (DM) production under irrigation was only 14% greater (not significant) than under dryland. In the pot experiment, DM production was significantly reduced, and water use efficiency (WUE) and chlorophyll content increased with reduced availability of water. The greater WUE induced by drought could have resulted from stomatal regulation and increased chlorophyll content. Carbon isotope ratios were correlated with the WUE, and may be utilized for selection to further improve the WUE of A. saligna under drought conditions.