Influence of dry season onQuercus suberL. leaf traits in the Iberian Peninsula

Abstract

Premise Water deficit and drought conditions are increasing in intensity, frequency, and duration in the Iberian Peninsula. We observed natural variation in leaf traits across the range of Quercus suber L. (cork oak), an ecologically important species within this region. Stomatal traits (e.g., pore length, maximum aperture) and carbon isotope composition (δ13C) provide an opportunity to examine the integrative effects of drought and dry‐season intensity on leaf development, maximum stomatal conductance, and adaptation to precipitation regimes. Methods Gross leaf traits (e.g., area, thickness), stomatal traits (e.g., pore length, size, aperture), and carbon isotope discrimination were measured in Q. suber leaves, and maximum stomatal conductance to water vapor (gwmax) was calculated. Trees were sampled from nine natural populations across a climate gradient in the Iberian Peninsula, including trees from two genetic lineages. Linear mixed models compared total water deficit to leaf traits, accounting for tree and site as random effects. Results Quercus suber gross leaf morphology remained consistent across the climate gradient, but increasing water deficit was correlated with smaller stomata at the leaf level and low δ13C at the tree level. No traits were significantly different between the two genetic lineages. Conclusions While there were no significant differences in gross leaf morphology across the climate gradient or between the genetic lineages, stomatal traits and δ13C responded to climate, suggesting that Q. suber can inhabit a range of environments in the Iberian Peninsula via micro‐adjustments of the trait that controls water loss into the atmosphere.

Chemical Composition of Cuticular Waxes and Pigments and Morphology of Leaves of Quercus suber Trees of Different Provenance

“…The cork oak leaves in the trees of all the provenances showed a clear schlerophytic character ( Figure 1 and Figure 2 ) and their morphological features ( Table 1 ) were within the range of values reported for the species. Leaf sizes (4.6–6.8 cm 2 ) were similar to those reported by Mediavilla et al [ 28 ] for Q. suber leaves taken from different orientations in the canopy (5.5–7.4 cm 2 ) and the 7.1 cm 2 reported by Prats et al [ 20 ]. The specific leaf area values (55.6–67.8 cm 2 /g) were of the same order of magnitude as those obtained in adult leaves of Q. suber growing under contrasting environments and located in different positions and orientations of the canopy (50.0 to 126.0 cm 2 /g) [ 28 , 29 , 30 , 31 , 32 ].…”

“…However, little information is available for Q. suber regarding natural variation in leaf morphology, cuticular features and phytochemical data, despite the fact that it has been demonstrated that the species possesses several mechanisms for drought tolerance including small and thick leaves, sclerophyllicity and deep tap-rooting [ 18 , 19 , 20 , 21 ]. Only one work was found in the literature regarding the cuticular waxes of Q. suber leaves [ 22 ]; for a sampling of two trees in spring and summer, the report described a composition including mainly n-alkyl esters (25–45% of the wax extract) and alkanols (18–50%), as well as alkanes, alkanals and alkanoic acids.…”

Quercus suber L. Genetic Resources: Variability and Strategies for Its Conservation

“…Leaf traits seem to show a certain degree of variability within the Q. suber populations [47,51]. Indeed, variability in leaf size, specific leaf area, and carbon isotope discrimination were found among populations of common garden trials, and this variability correlates with the annual rainfall of the habitat [51].…”

“…Overall, the studies herein described highlighted that Quercus species, and namely Q. suber, has a scattered distribution in which each region has different environmental conditions; therefore, each population is likely already adapted to its distribution area. Indeed, these studies show that genetic variation in Q. suber is geographically structured [33][34][35]47]. For a better understanding of historical events and their impact on Q. suber distribution range and differentiation, more studies are needed.…”

“…While genetics play a part, it seems that some trait variability found among lineages and among populations can be due to environmental conditions [34,47,49]. Cork oak populations have significant levels of phenotypic differentiation, as indicated by their morphological traits [50].…”