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Identifying consistent and predictable associations between traits and environment is one of the oldest quest of ecology. Yet, there are few formal and robust quantification of such associations, which seriously impedes our capacity to predict how ecological systems respond to global changes, including climate. This study was designed to assess how differences in environmental conditions affect plant form and function in a wide array of species.

Twelve traits were measured on 40 species in three Mediterranean sites differing in drought conditions. Some species being common among sites, 78 species belonging to four major Raunkiaer life form categories were studied. These traits correspond to: (i) plant size: vegetative and maximum plant height, (ii) seed mass, (iii) leaf morpho-anatomical traits: leaf area, specific leaf area, dry matter content and thickness, (iv) leaf chemical composition: mass based nitrogen, phosphorus and carbon contents, and carbon isotopic fraction.

On average, there was a shift in the phenotypic space towards more resource conservative and taller species in the drier sites. These changes were not always consistent for hemicryptophytes and chamaephytes on the one hand, and for phanerophytes on the other hand. This is interpreted as different species responding to different aspects of complex changes in environmental factors. Intraspecific trait variation differed among species, and was lower than interspecific variation. Changes in site-average trait values were therefore mostly driven by species turnover among sites.

The traits selected do not respond strongly to the differences in environmental conditions however, resulting in a moderate shift in the phenotypic space between sites. We argue that traits more directly related to plant water economy should be considered for an improved description of plant phenotypic response to the environmental factors at stake. The implications for the prediction of plant responses to climate changes likely to occur in the Mediterranean Region are discussed.