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.
Maria Jose Hernandez, Fernando Montes, Federico Ruiz, Gustavo Lopez, Pilar Pita, 2016, 'The effect of vapour pressure deficit on stomatal conductance, sap pH and leaf-specific hydraulic conductance inEucalyptus globulusclones grown under two watering regimes', Annals of Botany, vol. 117, no. 6, pp. 1063-1071 http://dx.doi.org/10.1093/aob/mcw031