We tested whether growth and maintenance costs of plant organs vary with environmental stress. Quercus ilex L. seedlings from acorns collected from natural populations in the northern Iberian Peninsula and in a lower elevation and putatively less stressful habitat in the southern Iberian Peninsula were grown in pots under the same conditions. Growth and maintenance respiration were measured by CO(2) exchange. Young leaves from 5-month-old seedlings of both populations had similar mean specific leaf areas, nitrogen and carbon concentrations and specific growth rates, and almost identical growth costs (1.26 g glucose g(-1)). Leaf maintenance cost was higher in northern than in the southern population (27.3 versus 22.4 mg glucose g(-1) day(-1), P < 0.01). In both populations, leaf maintenance cost decreased by 90% as leaves aged, but even in mature leaves, the maintenance cost was higher in the northern population than in the southern population (3.38 versus 2.53 mg glucose g(-1) day(-1), P < 0.01). The growth costs of fine roots < 1 mm in diameter were similar in the two populations (1.20 g glucose g(-1)), whereas fine root maintenance cost was higher in the northern population than in the southern population (9.86 versus 7.45 mg glucose g(-1) day(-1); P < 0.05). The results suggest that the cost of organ maintenance is related to the severity of environmental stress in the native habitat. Because the observed differences in both leaves and roots were constitutive, the two populations may be considered ecotypes.

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Aim Stressful environments, like those at the limits of species ranges, are closely associated with the selective establishment of particular traits, yet the mechanisms behind this relationship are poorly understood. Our main aim was to investigate spatial and temporal phenotypic plasticity related to environmental conditions and biogeographical origin.Location A latitudinal gradient along Iberian Peninsula and Morocco, western Mediterranean Basin. MethodsWe investigate the intra-specific variability in the Mediterranean oak Quercus ilex subsp. ballota, covering most of its latitudinal range. Acorns were collected in the years 2009, 2011, 2012 and 2013 from natural populations and were grown under controlled conditions. We measured acorn mass and germination dynamics, as well as seedling morphology.Results Field data showed significant differences in stand structure among populations. The southernmost population presented the smallest trees, followed by the northernmost population. Core-range trees registered higher values for leaf-nitrogen concentration. Leaf size showed latitudinal variation, with the lowest values at the northern range limit. In addition, the germination pattern also significantly differed among populations, showing a latitudinal pattern of variation (i.e. the southern populations germinated earlier). Fresh acorn mass showed significant within-and among-population differences, displaying a range margin pattern (i.e. similarities between the edge populations). Furthermore, seedling total weight and biomass allocation also followed the same pattern. The models explaining the most part of the trait variance were related mainly to climatic variables (reflecting temporal variability), while the random effect of the models (population) showed a range margin pattern with lower values in edge populations compared with core populations.Main conclusions Similar phenotypic traits among individuals native to the periphery of the distribution range were found despite the temporal variability, suggesting adaptation to stressful environments at the range edges.

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