Mediterranean Evergreen Species Research Articles

Leaf thickness and density drive the responsiveness of photosynthesis to air temperature in Mediterranean species according to their leaf habitus

The responsiveness of net photosynthetic rate (Aa) to mean monthly air temperature (TM) of eight Mediterranean evergreen species was investigated by analyzing the inter-annual changes in leaf mass area (LMA), leaf tissue density (LTD) and leaf thickness (LT). We wanted to test if species leaf habitus affected this response. To hit the goal, a multi-year dataset from our previously published papers was used. The inter-annual variability in LMA, LTD and LT was assessed by their coefficients of variation (CVs). Aa sensitivity to TM (SAa) was quantified by the slope of the species-specific relationships Aa-TM. A Principal Component Analysis (PC) was carried to identify the leaf morphological variation patterns across species. SAa was affected by the coordination of LTD and LT across species and this coordination depended on leaf habitus. The relationship between CVs and SAa revealed that only evergreen sclerophyllous with a longer leaf life-span rely on the inter-annual changes in LTD and LT to modulate their SAa. Overall, the results showed that the inter-annual LTD and LT variability affected the responsiveness of net photosynthetic rate of the selected species according to their leaf habitus.

Evergreen species response to Mediterranean climate stress factors

Abstract: Recent climatic projections predict a decline in rainfall mainly during the summer period and an increase in air temperature for the Mediterranean basin, resulting in extended periods of soil water deficit. Mediterranean evergreen species attain drought resistance through different traits or combination of traits. The main objective of this research is to analyze the response of the evergreen species co-occurring in the Mediterranean maquis to variations in water availability and air temperature during the year. The results show that leaf structural traits significantly affect physiological traits as confirmed by the Partial Least Squares Regression analysis (PLS). In particular, the considered species have a similar leaf respiration (RL) trend during the year with the lowest rates in winter (mean 0.95 ± 0.44 µmol m-2 s-1) and the highest in drought (mean 3.05 ± 0.96 µmol m-2 s-1). Nevertheless, a different RL effect on gross photosynthesis (PG) during drought was observed. C. incanus, E. multiflora, R. officinalis and S. aspera have the highest RL/PG ratio (mean 0.54 ± 0.08), while Q. ilex, P. latifolia, P. lentiscus, A. unedo and E. arborea have the lowest (mean 0.22 ± 0.07). RL/PG ratio variations depend on the sensitivity of both the two parameters to drought. Considering the increase of the length and intensity of drought in the Mediterranean basin, and that the photosynthesis of Mediterranean evergreen species is frequently limited by sub-optimal conditions (i.e., water deficit, high light intensity and high air temperature), it is important to improve knowledge on RL, since it has a critical function in modulating carbon balance of Mediterranean species.

Litterfall and growth dynamics relationship with the meteorological variability in three forests in the Montseny natural park

Abstract We assessed the influence of some environmental conditions (temperature and rainfall) on the litterfall and BAI (basal area increment), in three close forests in the Montseny massif (NE part of the Iberian peninsula, Spain). Two of them are composed of deciduous species Fagus sylvatica and Quercus petraea, and the other one is a Mediterranean evergreen species, Quercus ilex. We have collected monthly data about litterfall and radial growth since 2007. For each forest there are tree plots, with litterfall traps and band dendrometers. This data has been related with the meteorological parameters of meteorological station closed to the study area. Our results show that F. sylvatica recorded the biggest drop in annual litterfall (6 Mg·ha−1·year−1), followed by Q. ilex (4.34 Mg·ha−1·year−1) and Quercus petraea (4.4 Mg·ha−1·year−1) and that all the values were similar to those observed in other forests and mountains with the same state of maturity. Regarding the litterfall, the investigation found a decline in the leaves fall in deciduous trees in years with hot summers. In addition, these warm summers produce a decline in the F. sylvatica BAI, but not in Q. petraea. Concerning growth, we found that Q. petraea increases the BAI on the study period while F. sylvatica does not. In conclusion, we believe that in the future Q. petraea will be more tolerant to the warm conditions than F. sylvatica, making the former a possible replacement of the second species.

Variations in leaf respiration and photosynthesis ratio in response to air temperature and water availability among Mediterranean evergreen species

Net photosynthesis (PN) and leaf respiration (RL) of the evergreen species co-occurring in the Mediterranean maquis in response to water availability and air temperature variations were analyzed. The results underlined that the ratio RL/PN of the considered species ranged from 0.15 ± 0.08 (in winter) to 1.32 ± 0.80 (in summer). Variations of RL and PN during the year were attested by the PCA which was carried out using leaf physiological and morphological traits of the considered species. In particular, Cistus incanus having the highest mean yearly PN and RL rates and low leaf mass area (LMA) and leaf tissue density (LTD), was furthest from the other species emphasizing its drought semi-deciduous habitus, the highest photosynthetic capability in favorable conditions (spring), but low tolerance to drought. Erica multiflora and Rosmarinus officinalis were characterized by the highest LMA and LTD, low PN rates in drought and the lowest PN ones in spring. Erica arborea, Pistacia lentiscus, Phillyrea latifolia and Quercus ilex had the highest drought tolerance. Arbutus unedo and Smilax aspera were close to this group despite lower RL rates during the year. The xeromorphic leaves of the considered evergreen species (i.e. high LMA and LTD) favor carbon gain profits over transpiration losses during drought, nevertheless, the high construction cost of these leaf type justifies the relatively high RL rates.

Variations in leaf respiration across different seasons for Mediterranean evergreen species

Leaf respiration (R L) of evergreen species co-occurring in the Mediterranean maquis developing along the Latium coast was analyzed. The results on the whole showed that the considered evergreen species had the same R L trend during the year, with the lowest rates [0.83 ± 0.43 μmol(CO2) m-2 s-1, mean value of the considered species] in winter, in response to low air temperatures. Higher R L were reached in spring [2.44 ± 1.00 μmol(CO2) m-2 s-1, mean value] during the favorable period, and in summer [3.17 ± 0.89 μmol(CO2) m-2 s-1] during drought. The results of the regression analysis showed that 42% of R L variations depended on mean air temperature and 13% on total monthly rainfall. Among the considered species, C. incanus, was characterized by the highest R L in drought [4.93 ± 0.27 μmol(CO2) m-2 s-1], low leaf water potential at predawn (Ψpd= -1.08 ± 0.18 MPa) and midday (Ψmd = -2.75 ± 0.11 MPa) and low relative water content at predawn (RWCpd = 80.5 ± 3.4%) and midday (RWCmd = 67.1 ± 4.6%). Compared to C. incanus, the sclerophyllous species (Q. ilex, P. latifolia, P. lentiscus, A. unedo) and the liana (S. aspera), had lower R L [2.72 ± 0.66 μmol(CO2) m-2 s-1, mean value of the considered species], higher RWCpd (91.8 ± 1.8%), RWCmd (82.4 ± 3.2%), Ψpd (-0.65 ± 0.28 MPa) and Ψmd (-2.85 ± 1.20 MPa) in drought. The narrow-leaved species (E. multiflora, R. officinalis, and E. arborea) were in the middle. The coefficients, proportional to the respiration increase for each 10°C rise (Q10), ranging from 1.49 (E. arborea) to 1.98 (A. unedo) were indicative of the different sensitivities of the considered species to air temperature variation.

Stomatal encryption by epicuticular waxes as a plastic trait modifying gas exchange in a Mediterranean evergreen species (Quercus coccifera L.)

The adaptive benefit of stomatal crypts remains a matter of controversy. This work studies the effect on gas exchange of cuticular rims that overarch the stomatal pore in the Mediterranean species Quercus coccifera L. growing under Mediterranean (lower relative humidities and high summer temperatures) or oceanic conditions (higher daily relative humidities and mild temperatures). After microscopic assessment of the leaf surfaces and stomatal architecture, the impact of the cuticular 'cup' on gas exchange was evaluated by employing three-dimensional finite element models. Here, we provide evidence for a high plasticity of the Q. coccifera cuticular cup, with much larger vents under oceanic conditions compared to small vents under Mediterranean conditions. This structure adds a substantial fixed resistance thereby strongly decreasing gas exchange under Mediterranean conditions. The cuticular cup, which also increases leaf internal humidity, might buffer the rapid changes in vapour pressure deficit (VPD) often observed under Mediterranean conditions. Since water loss of guard and adjacent epidermal cells regulates stomatal aperture, we suggest that this structure allows an efficient regulation of stomatal conductance and optimum use of resources under high VPD. This study provides evidence that plasticity of stomatal architecture can be an important structural component of hydraulic adaptation to different climate conditions.

Relating ring width of Mediterranean evergreen species to seasonal and annual variations of precipitation and temperature

Abstract. Plant growth in Mediterranean landscapes is limited by the typical summer-dry climate. Forests in these areas are only marginally productive and may be quite susceptible to modern climate change. To improve our understanding of forest sensitivity to annual and seasonal climatic variability, we use tree-ring measurements of two Mediterranean evergreen tree species: Quercus ilex L. and Arbutus unedo L. We sampled 34 stems of these species on three different types of substrates in the Peyne study area in southern France. The resulting chronologies were analysed in combination with 38 yr of monthly precipitation and temperature data to reconstruct the response of stem growth to climatic variability. Results indicate a strong positive response to May and June precipitation, as well as a significant positive influence of early-spring temperatures and a negative growth response to summer heat. Comparison of the data with more detailed productivity measurements in two contrasting years confirms these observations and shows a strong productivity limiting effect of low early-summer precipitation. The results show that tree-ring data from Q.ilex and A.unedo can provide valuable information about the response of these tree species to climate variability, improving our ability to predict the effects of climate change in Mediterranean ecosystems.

Leaf expansion in Rhamnus alaternus L. by leaf morphological, anatomical and physiological analysis

Morphological, anatomical and physiological traits of Rhamnus alaternus during leaf expansion were analysed. Bud break occurred when mean air temperature was 14.1 ± 1.2°C, and it was immediately followed by the increase of leaf area and leaf dry mass. The highest leaf expansion rates happened during the first 22 days of the process. Leaf area and leaf dry mass reached the steady-state value 46 and 62 days after bud break, respectively. Net photosynthesis increased from bud break to full leaf expansion, and total chlorophyll content had the same trend, confirmed by the correlation between the two variables. Leaf dark respiration peaked during the first 11 days of leaf expansion, then decreased and reached a steady-state value 34 days after bud break. R. alaternus completed cell division and cell enlargement of the epidermal tissue 28 days after bud break, and the ones of the mesophyll tissue at full leaf expansion. The results underline that morphological, anatomical and physiological leaf traits in R. alaternus are indicative of a less sclerophyllous species (i.e. higher specific leaf area) compared with other Mediterranean evergreen species. Moreover, the higher fraction of mesophyll volume occupied by the intercellular air spaces, and the ability to end the leaf expansion process before air temperature might be a limiting factor, makes R. alaternus closer to the mesophyte species.

Relationship between net photosynthesis and leaf respiration in Mediterranean evergreen species

The relationship between net photosynthetic (P N) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P N during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean P N (16.4±2.4 µmol m−2 s−1) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 µmol m−2 s−1). The highest R (1.89±0.30 µmol m−2 s−1, mean of the species), associated to a significant P N decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/P N ratio 0.447±0.091). Q10, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/P N determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P N and lower R during stress periods.

Physiological response of eight Mediterranean maquis species to low air temperatures during winter

We analyzed the physiological response of the Mediterranean evergreen species (Arbutus unedo L., Cistus incanus L., Erica arborea L., Erica multiflora L., Phillyrea latifolia L., Pistacia lentiscus L., Quercus ilex L., and Rosmarinus officinalis L.) to winter low air temperatures. In occasion of two cold events, in February 2005 (T min = 1.8 °C), and January 2006 (T min = 3.1 °C and minimum T air = -0.40 °C during the nights preceding the measurements), R. officinalis, C. incanus, and E. multiflora had the highest net photosynthetic rate (P N) decrease (73 %, mean value) with respect to the winter P N maximum, followed by A. unedo (62 %), P. latifolia and P. lentiscus (54 %, mean value), E. arborea (49 %), and Q. ilex (44 %). Among the considered species, Q. ilex was able to maintain P N near the maximum for 150 min during the day, A. unedo, P. lentiscus, E. arborea, P. latifolia, E. multiflora, and R. officinalis for 60 min, and C. incanus for 30 min. The calculated mean winter daily P N ranged from 7.9±0.6 (Q. ilex) to 2.8±0.5 (R. officinalis) µmol(CO2) m-2 s-1. During the study period, chlorophyll (Chl) content decreased by 36 % on an average in the two cold events, and the carotenoid (Car) to Chl ratio increased by 133 % in Q. ilex, having the highest value in January 2006. Principal component analysis underlined the highest cold resistance of Q. ilex by high P N and high Car/Chl ratio. On the contrary, R. officinalis and C. incanus had the lowest cold resistance by the highest P N decrease and the lowest Car/Chl (C. incanus). Thus, winter stress could be an additional limitation to Mediterranean evergreen species production, and the capacity of the species to maintain P N near 90-100 % during winter is determinant for biomass accumulation.

Major diffusion leaks of clamp‐on leaf cuvettes still unaccounted: how erroneous are the estimates of Farquhar et al. model parameters?

Estimates of leaf gas-exchange characteristics using standard clamp-on leaf chambers are prone to errors because of diffusion leaks. While some consideration has been given to CO(2) diffusion leaks, potential water vapour diffusion leaks through chamber gaskets have been neglected. We estimated diffusion leaks of two clamp-on Li-Cor LI-6400 (Li-Cor, Inc., Lincoln, NE, USA) leaf chambers with polymer foam gaskets and enclosing either 2 or 6 cm(2) leaf area, and conducted a sensitivity analysis of the diffusion leak effects on Farquhar et al. photosynthesis model parameters - the maximum carboxylase activity of ribulose 1 x 5-bisphosphate carboxylase/oxygenase (Rubisco) (V(cmax)), capacity for photosynthetic electron transport (J(max)) and non-photorespiratory respiration rate in light (R(d)). In addition, net assimilation rate (A(n)) versus intercellular CO(2) (C(i)) responses were measured in leaves of Mediterranean evergreen species Quercus ilex L. enclosing the whole leaf chamber in a polyvinyl fluoride bag flushed with the exhaust air of leaf chamber, thereby effectively reducing the CO(2) and water vapour gradients between ambient air and leaf chamber. For the empty chambers, average diffusion leak for CO(2), K(CO2), (molar flow rate corresponding to unit CO(2) mole fraction difference) was ca. 0.40 micromol s(-1). K(CO2) increased ca. 50% if a dead leaf was clamped between the leaf chamber. Average diffusion leak for H(2)O was ca. 5- to 10-fold larger than the diffusion leak for CO(2). Sensitivity analyses demonstrated that the consequence of a CO(2) diffusion leak was apparent enhancement of A(n) at high CO(2) mole fraction and reduction at lower CO(2) mole fraction, and overall compression of C(i) range. As the result of these modifications, Farquhar et al. model parameters were overestimated. The degree of overestimation increased in the order of V(cmax) < J(max) < R(d), and was larger for smaller chambers and for leaves with lower photosynthetic capacity, leading to overestimation of all three parameters by 70-290% for 2 cm(2), and by 10-60% for 6 cm(2) chamber. Significant diffusion corrections (5-36%) were even required for leaves with high photosynthetic capacity measured in largest chamber. Water vapour diffusion leaks further enhanced the overestimation of model parameters. For small chambers and low photosynthetic capacities, apparent C(i) was simulated to decrease with increasing A(n) because of simultaneous CO(2) and H(2)O diffusion leaks. Measurements in low photosynthetic capacity Quercus ilex leaves enclosed in 2 cm(2) leaf chamber exhibited negative apparent C(i) values at highest A(n). For the same leaves measured with the entire leaf chamber enclosed in the polyvinyl fluoride bag, C(i) and A(n) increased monotonically. While the measurements without the bag could be corrected for diffusion leaks, the required correction in A(n) and transpiration rates was 100-500%, and there was large uncertainty in Farquhar et al. model parameters derived from 'corrected'A(n)/C(i) response curves because of uncertainties in true diffusion leaks. These data demonstrate that both CO(2) and water vapour diffusion leaks need consideration in measurements with clamp-on leaf cuvettes. As plants in natural environments are often characterized by low photosynthetic capacities, cuvette designs need to be improved for reliable measurements in such species.

Complex adjustments of photosynthetic potentials and internal diffusion conductance to current and previous light availabilities and leaf age in Mediterranean evergreen species Quercus ilex

Mature non-senescent leaves of evergreen species become gradually shaded as new foliage develops and canopy expands, but the interactive effects of integrated light during leaf formation (Q(int)G), current light (Q(int)C) and leaf age on foliage photosynthetic competence are poorly understood. In Quercus ilex L., we measured the responses of leaf structural and physiological variables to Q(int)C and Q(int)G for four leaf age classes. Leaf aging resulted in increases in leaf dry mass per unit area (M(A)), and leaf dry to fresh mass ratio (D(F)) and decreases in N content per dry mass (N(M)). N content per area (N(A)) was independent of age, indicating that decreases in N(M) reflected dilution of leaf N because of accumulation of dry mass (NA = N(M) M(A)). M(A), D(F) and N(A) scaled positively with irradiance, whereas these age-specific correlations were stronger with leaf growth light than with current leaf light. Area-based maximum ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylase activity (V(cmax)A), capacity for photosynthetic electron transport (J(max)A) and the rate of non-photorespiratory respiration in light (R(d)A) were also positively associated with irradiance. Differently from leaf structural characteristics, for all data pooled, these relationships were stronger with current light with little differences among leaves of different age. Acclimation to current leaf light environment was achieved by light-dependent partitioning of N in rate-limiting proteins. Mass-based physiological activities decreased with increasing leaf age, reflecting dilution of leaf N and a larger fraction of non-photosynthetic N in older leaves. This resulted in age-dependent modification of leaf photosynthetic potentials versus N relationships. Internal diffusion conductance (g(m)) per unit area (g(m)A) increased curvilinearly with increasing irradiance for two youngest leaf age classes and was independent of light for older leaves. In contrast, g(m) per dry mass (g(m)M) was negatively associated with light in current-year leaves. Greater photosynthetic potentials and moderate changes in diffusion conductance resulted in greater internal diffusion limitations of photosynthesis in higher light. Both area- and mass-based g(m) decreased with increasing leaf age. The decrease in diffusion conductance was larger than changes in photosynthetic potentials, leading to larger CO2 drawdown from leaf internal air space to chloroplasts (delta(c)) in older leaves. The increases in diffusion limitations in older leaves and at higher light scaled with age- and light-dependent increases in MA and D(F). Overall, our study demonstrates a large potential of foliage photosynthetic acclimation to changes in leaf light environment, but also highlights enhanced structural diffusion limitations in older leaves that result from leaf structural acclimation to previous rather than to current light environment and accumulation of structural compounds with leaf age.

Seasonal changes in photosynthesis and photoprotection in a Quercus ilex subsp. ballota woodland located in its upper altitudinal extreme in the Iberian Peninsula

Quercus ilex L. subsp. ballota (Desf.) Samp., a Mediterranean evergreen species growing in a continental Mediterranean climate, did not experience water stress and showed greater sensitivity to winter stress than to summer stress over a 12-month period. Net CO2 assimilation rates and photosystem II (PSII) efficiency decreased markedly during the cold months and recovered completely in spring. Lutein, neoxanthin and beta-carotene to chlorophyll (Chl) molar ratios all showed the same trend throughout the year, increasing from September to March. This increase was a result of increases in carotenoid concentrations, because Chl concentration per unit leaf area remained stable, and was higher at the end than at the beginning of the first growing season. Lutein-epoxide was a minor component of the total lutein pool. Thermal energy dissipation and non-photochemical quenching (NPQ) were associated with the de-epoxidated forms of the xanthophyll cycle pigments in the warm months. Photosynthetic rates decreased slightly at midday in summer. These changes were accompanied by decreases in maximum potential PSII efficiency (which recovered during the night), actual and intrinsic PSII efficiencies, photochemical quenching and increases in NPQ. Overall, our data indicate down-regulation of photosynthesis during the summer. The diurnal de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin occurred throughout the year, except in January. Antioxidant enzymatic activity increased in the winter months, especially during the coldest months, highlighting its key role in photoprotection against photo-oxidation. Structural and functional modifications protected PSII from permanent damage and allowed 1-year-old leaves to photosynthesize at high rates when temperatures increased in spring.

The effect of low temperatures on the photosynthetic apparatus of Quercus ilex subsp. ballota at its lower and upper altitudinal limits in the Iberian peninsula and during a single freezing-thawing cycle

We investigated the response of the photosyn- thetic apparatus during an episode of extreme low winter temperature in Quercus ilex subsp. ballota (Desf.) Samp., a typical Mediterranean evergreen species in the Iberian peninsula. Both plants in a woodland located at high altitude (1,177 m. a.s.l.) and potted plants obtained from acorns of the same populations grown at low altitude (225 m. a.s.l.) were analyzed. Net CO2 assimilation rate was negative and there was a marked decrease in photosystem II (PSII) efficiency during winter in leaves of the woodland population (high altitude individuals). These processes were accompanied by increases in non- photochemical quenching (NPQ) and in the de-epoxidated carotenoids within the xanthophyll cycle, mechanisms aimed to dissipate excess energy. In addition, these de- epoxidated carotenoids were largely preserved during the night. There was no chlorophyll bleaching during the winter, which suggests that leaves were not experiencing photoinhibitory damage. In fact, the net photosynthetic rate and the PSII efficiency recovered in spring. These changes were not observed, or were much more reduced, in individuals located at lower altitude after a few frosts. When the response to rapid temperature changes (from 20°C to �5°C and from �5°C to 20°C) was studied, it was found that the maximum potential PSII efficiency was fairly stable, ranging from 0.70 to 0.75. The rest of the photosynthetic parameters measured, actual and intrinsic PSII efficiency, photochemical and NPQ, responded immediately to the changes in temperature and, also, the recovery after cold events was practically immediate.

Effects of ozone on the foliar histology of the mastic plant ( Pistacia lentiscus L.)

An open-top chamber study was conducted to investigate the tissue and cellular-level foliar effects of ozone (O 3) on a Mediterranean evergreen species, the mastic plant ( Pistacia lentiscus L.). Plants were exposed at three different O 3 levels, and leaf samples were collected periodically from the beginning of the exposure. Although no visible foliar injury was evident, alterations of the plastids and vacuoles in the mesophyll were observed. Senescence processes were accelerated with an anomalous stacking of tannin vacuoles, and a reduction in the size and number of the chloroplasts. Overall, most of the modifications induced by O 3 were consistent with previously reported observations on deciduous broadleaf species, with the exception of alterations in the cells covering the secretory channels, reported here as a new finding. Comments on the feasibility of using microscopy to validate O 3 related field observations and subtle foliar injury are also given.

Photoprotection in evergreen Mediterranean plants during sudden periods of intense cold weather

The photoprotective responses to an abrupt period of exceptional cold weather were studied in several Mediterranean evergreen species with different ecological requirements. The same pattern of response was observed in most of the species with little change in hydrophilic antioxidants (ascorbate and glutathione) and the carotenoid pool, an increase in the content of α -tocopherol, and a night retention of de-epoxidised xanthophylls (antheraxanthin and zeaxanthin). The accumulation of these xanthophylls correlated with a sustained decrease in maximal photochemical efficiency (Fv/Fm). This reduction in the rate of electron transport would reduce the production of superoxide in photosystem I, as well as the subsequent hydrogen peroxide and hydroxyl radical. Thereby if any transitory photooxidative stress is produced under these conditions it should be due mainly to the formation of singlet oxygen by triplet excited chlorophyll within the antenna. Since α-tocopherol is the main scavenger of singlet oxygen and lipid peroxy radicals, the large increase of this antioxidant within the species could be enough to compensate for the higher degree of photooxidative stress, playing an essential role in the survival of vegetation during the incidence of exceptional cold fronts in the Mediterranean region.

Functional groups in Quercus species derived from the analysis of pressure–volume curves

Oaks that occupy Mediterranean phytoclimates share common leaf features (evergreenness, high leaf dry mass per unit area, LMA). Due to this phytoclimatic, morphological, and phenological convergence it has been suggested that they might constitute a coherent functional group. To confirm this hypothesis, some physiological parameters were determined after calculating pressure–volume curves (P–V curves) using the free-transpiration method. Seventeen Quercus species from contrasting phytoclimates were studied: six Mediterranean evergreen species (Q. agrifolia, Q. chrysolepis, Q. coccifera, Q. ilex ssp. ballota, Q. ilex ssp. ilex, and Q. suber); seven nemoral deciduous species (Q. alba, Q. laurifolia, Q. nigra, Q. petraea, Q. robur, Q. rubra and Q. velutina), and four nemoro-Mediterranean deciduous species (Q. cerris, Q. faginea, Q. frainetto, and Q. pyrenaica). Two-year-old seedlings growing under homogeneous environmental conditions (no water restrictions, uniform light, and nutrient supply) were used. The statistical analyses (correlation, mean-value comparisons, principal component analysis) of leaf features and parameters derived from the P–V curves confirmed the functional homogeneity of the three phytoclimatic groups, which were characterized by their contrasting ecophysiological response to water stress. The Mediterranean oak species developed mechanisms to avoid an excessive loss of cell water (e.g. high cell-wall rigidity). Conversely, the nemoral oaks showed the opposite. The nemoro-Mediterranean oaks perform better than nemoral oaks under water-stress conditions, but they cannot perform as well as the Mediterranean oaks on relatively dry soils.