Abstract: Aims The limited water supply in the Mediterranean Basin will be exacerbated in the immediate future as result of severe drought events. Thus, the study of the intraspecific variability in functional traits of plant species is important, because such variability modulates species' responses. Here, we aimed to analyse the variability in plasticity of physiological and structural traits of Arbutus unedo L. in response to water availability and to determine whether the levels of phenotypic plasticity varied in plants of different provenances.
Methods We kept two sets of plants under contrasted water regimes (high water and low water) and calculated a phenotypic plasticity index to determine the plastic response to water stress. We compared the response among kind of traits and provenance. We also performed analysis of variance to assess the trait and provenance effect.
Important findings We found that biomass and key physiological traits decrease under drought conditions, while the water use efficiency increased. Plasticity differed between groups of traits, being higher in structural and gas exchange parameters, but the provenance did not account for significant variation in plasticity. A. unedo has evolved a 'good saver' strategy, involving decreasing growth and water use—when this resource is unavailable—together with the dissipation of excess of radiation that it cannot process. The homogeneous response between provenances may be the result of a canalization event. This strategy, based on a high degree of plasticity, is a probable determining factor in the success of the species over its wide range of environmental conditions and will be critical to withstand the ongoing environmental changes.

Key words: adaptation, canalization, contrasted provenances, drought, global change, phenotypic plasticity