Ecophysiological and structural traits of seedlings of the water-saver Pinus halepensis and the water-spenders Quercus coccifera and Q. ilex were studied in response to water stress under greenhouse conditions. Water deficit reduced stomatal conductance (g s ) and, as a consequence, both net CO 2 assimilation (A) and transpiration rate (E) were also reduced. Water stress also emphasized midday downregulation of the photochemical efficiency (dynamic photoinhibition) reducing quantum yield of noncyclic electron transport ( PSII ), photochemical quenching (qP) and photochemical efficiency of the open reaction centres of PSII (F v /F m ) and involved an increase of thermal dissipation of excess energy. However, water stress not only induced dynamic photoinhibition but also brought a reduction in F v /F m (chronic photoinhibition). Despite the water-saving strategy of P. halepensis that limited net CO 2 assimilation, this species showed a higher photochemical efficiency and lower photoinhibition than Quercus species. This was not the result of a different photochemical quenching but was linked to a higher value of F v /F m , indicating a less severe photo-inactivation of PSII. Water stress resulted in a loss of pigment content and in an increase of the carotenoids/chlorophyll ratio, antioxidant capacity and the biomass rate allocated to roots as opposed to that assigned to leaves. P. halepensis showed a Communicated by M. Ball

The Mediterranean evergreen woody plants Quercus coccifera and Pinus halepensis grow in a range of environments where selection by drought, heat and high irradiance can drive genetic and phenotypic diVerentiation of populations. However, the role of these stresses in Wltering out maladaptive genotypes remains unknown. We hypothesize that this Wltering is an important process for woody Mediterranean species due to their low phenotypic plasticity reported in previous studies. We have studied the response of saplings of Q. coccifera and P. halepensis, originating from two contrasting populations (a rock outcrop and a garrigue formation), to water stress. Isozyme characterization of genetic diversity was done to determine whether populations were genetically distinct. Water response analysis was based on water relations, gas exchange, chlorophyll a Xuorescence, pigment content, antioxidant status and morphological and structural parameters. Ecotypic diVerentiation was found for both Q. coccifera and P. halepensis populations, with a higher population isozyme similarity and a higher frequency of dominance of a few genotypes at the rock outcrop in both the species. P. halepensis exhibited small but signiWcant diVerences between populations for plastic responses to water, with lower phenotypic plasticity in saplings from the rock outcrop. Although it was not found in Q. coccifera, this pattern suggests that ecotypic diVerentiation rendering stress-tolerant ecotypes involves a decreased plasticity. Phenotypic plasticity was not high but it explained over 75% of the total variability among individual plants. Thus, and although evidence for ecotypic divergence was found in both the species, saplings were plastic enough to blur ecotypic diVerentiation.

We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature.

Summary  Quercus coccifera, a slow‐growing, evergreen oak, grows in contrasting environments in the Mediterranean Basin. Habitat‐based selection may have promoted divergence between populations with respect to phenotypic plasticity and genetic variability.  We tested the hypothesis that populations of the Q. coccifera originating from a rock outcrop, a continental garrigue formation and an oceanic forest would differ in their plastic response to light intensity. Plants from these populations were grown from acorns in a common garden at 100% and 20% full sunlight. Light response analysis was based on photochemical efficiency, xanthophyll pool, nutrient allocation, growth, crown architecture and light absorption.  Light‐responsive characters ranged from the subcellular to the whole‐plant level. The greatest divergences between sun and shade phenotypes were observed in leaf size, leaf angle and leaf area ratio. However, plasticity in these traits depended on plant provenance.  Regardless of the level of organization, populations were invariably ranked in the same order of plasticity when averaged over light‐responsive features, with plants originating from the rock outcrop showing the least plasticity and those from the forest the largest. The forest population also had the greatest genetic variability with respect to the isoperoxidase polymorphism. Among populations, plants originating from the phosphorus‐deficient rock outcrop contained 30% more P per unit dry weight. Plants from the forest population had 5% more photoprotective xanthophylls, 30% larger total leaf area, with less lobed and larger leaves and a differential plasticity in leaf azimuth. Differences among populations suggested ecotypic differentiation towards less phenotypic plasticity in the most homogeneous light environments. The ecological breadth of the species seemed to be derived not only from its tolerance of Mediterranean conditions but also from the specialization of its populations in contrasting habitats.