Guillermo Goldstein is Smathers Professor in Tropical Tree Biology at University of Miami, FL. He received his PhD in Ecophysiology (1981) and Master in Botany from University of Washington, Seattle (1978). He is the Reviewer for the international journals of Ecology, Biotropica, Journal of Arid Environments, Journal of Tropical Ecology, Journal of Theoretical Biology, Plant and Soil, Oecologia Plantarum, Journal of Experimental Botany, Oecologia, Acta Oecologica, Plant Cell and Environment, Functional Ecology, International Journal of Plant Science, TREE (Trends in Ecology and Evolution), Tree Physiology, New Phytologist. And also subject editor of Australian Journal of Botany, Tree Physiology, Acta Oecologica.
We studied physiological changes resulting from acclimation to low temperatures in order to understand the increased supercooling capacity in stems and leaves of Olea europaea. We measured during summer and winter seasons, water relations and hydraulic traits, ice nucleation temperature (INT) and the lethal temperature (LT50) in five olive cultivars which exhibit supercooling in all tissues as a freezing avoidance mechanism. All cultivars showed a gradual decrease in INT and LT50 from the dry and warm summer to the wet and cold winter. During acclimation there was an increase in cell wall rigidity and stomatal conductance (gs), as well as a decrease in apoplastic water content, leaf water potential (Ψ), sap flow and stem hydraulic conductivity (ks). Low Ψ as consequence of high gs and the effects of low temperatures on root activity resulted in a substantial loss of ks. A ks decrease was directly related to the decrease in INT across cultivars. Thus the loss of freezable water from xylem vessels by embolism formation increases stem supercooling capacity and delay ice propagation to the leaves. For the first time a trade-off between water transport efficiency and supercooling capacity was observed. Embolism formation, far from being a carbon cost was helpful for avoiding extracellular ice formation.