Stomatal sensitivity to vapour pressure deficit relates to climate of origin in Eucalyptus species

Selecting plantation species to balance water use and production requires accurate models for predicting how species will tolerate and respond to environmental conditions. Although interspecific variation in water use occurs, species-specific parameters are rarely incorporated into physiologically based models because often the appropriate species parameters are lacking. To determine the physiological control over water use in Eucalyptus, five stands of Eucalyptus species growing in a common garden were measured for sap flux rates and their stomatal response to vapour pressure deficit (D) was assessed. Maximal canopy conductance and whole-canopy stomatal sensitivity to D and reduced water availability were lower in species originating from more arid climates of origin than those from humid climates. Species from humid climates showed a larger decline in maximal sap flux density (J(Smax)) with reduced water availability, and a lower D at which stomatal closure occurred than species from more arid -climates, implying larger sensitivity to water availability and D in these species. We observed significant (P < 0.05) correlations of species climate of origin with mean vessel diameter (R-2 = 0.90), stomatal sensitivity to D (R-2 = 0.83) and the size of the decline in J(Smax) to restricted water availability (R-2 = 0.94). Thus aridity of climate of origin appears to have a selective role in constraining water-use response among the five Eucalyptus plantation species. These relationships emphasize that within this congeneric group of species, climate aridity constrains water use. These relationships have implications for species choices for tree plantation success against drought-induced losses and the ability to manage Eucalyptus plantations against projected changes in water availability and evaporation in the future.