Water relations, xylem embolism, root and shoot hydraulic conductance of both young plants in the field and
potted seedlings of Quercus pubescens have been studied with the aim of investigating whether these variables may
account for the well known adaptation of this oak species to arid habitats. Our data revealed that Q. pubescens is
able to maintain high leaf relative water contents under water stress conditions. In fact, relative water contents
measured in summer (July) did not differ from those recorded in April. This was apparently achieved by
compensating water loss by an equal amount of water uptake. Such a drought avoidance strategy was made
possible by the recorded high hydraulic efficiency of stems and roots under water stress. In fact, root hydraulic
conductance of field-grown plants was maintained high in summer when the percentage loss of hydraulic
conductance of stems was lowest. The hydraulic architecture of young plants of Q. pubescens measured in terms
of partitioning of hydraulic resistances along the water pathway revealed that the highest hydraulic resistance was
located in stems of the current year's growth. This hydraulic architecture is interpreted as consistent with the
adaptation of Q. pubescens to arid habitats as a consequence of the recorded seasonal changes in water relation
parameters as well as in root and stem hydraulics.