Selected Eucalyptus globulus clones can grow to a height of up to 14m in 3 years, receiving an average rainfall of 630 mm year–1 with a 4-month summer drought. Working with plants under a year old from five clones, Hernández et al. found that xylem sap pH decreased as water potential and stomatal conductance decreased under increasing vapour pressure deficits.
Stomata closed after a significant amount of hydraulic conductance was lost, but precluded water potential from decreasing below –1.8MPa. These results suggest a coordinated response aimed at preserving the hydraulic sufficiency of the stem and resulting in sap acidification.