Sclerophylly and Plant Water Relations in Three Mediterranean Quercus Species

The possible role in drought resistance played by sclerophyllywas studied in the Mediterranean oaks Quercus ilex, Q. suberand Q. pubescens. Studies were conducted on leaves at 30, 50and 80% of their final surface area, as well as on mature leavesof the current year's growth in June and September and on 1-year-oldleaves. Leaves of different ages of the three species showed quite differentdegrees of sclerophylly (DS). Q. ilex leaves reached the definitiveDS of 1.75 g dm^–2 during leaf expansion; Q. pubescensleaves hardened at the end of their expansion, with a finalDS of 0.93 g dm^–2; Q. suber showed the lowest DS of 0.76g dm^–2. Leaf conductance to water vapour (g₁) of 1-year-old leaves ofQ. ilex, measured in the field, showed a duration of the g₁peak values about twice that of the other two species. The minimumleaf relative water content (RWC), however, was near the samein the three species, indicating that water loss was recoveredpartly by Q. ilex leaves. This was apparently due to the higherbulk modulus of elasticity (