Drought and light anatomical adaptive leaf strategies in three woody species caused by microclimatic selection at 'Evolution Canyon', Israel

Seven structural and morphological characteristics of leaves from three woody species (Olea europaea, Ceratonia siliqua, and Pistacia lentiscus) were quantified for trees and shrubs from 'Evolution Canyon', Lower Nahal Oren microsite, Mount Carmel, Israel. Our results indicate overall parallel and species-specific leaf xeromorphic interslope microclimatic adaptations. Leaves of all three species from the south-facing slope (SFS) were smaller than those from the north-facing slope (NFS). Leaves of O. europaea and C. siliqua on the SFS were significantly thicker than those on the NFS due to increased thickness of the two photosynthetic parenchyma layers, the palisade and spongy layers. A similar significantly increased thickness of the spongy layer was found in leaves of P. lentiscus. The opposite trend was found in the palisade layer thickness of this species. Thicker epidermis was found in SFS as compared to NFS leaves of O. europaea and P. lentiscus, while the reverse was found in C. siliqua. Palisade cells in SFS leaves of C. siliqua and P. lentiscus were significantly longer than in leaves from the NFS, while the opposite trend was found in O. europaea. Discriminant analysis succeeded in differentiating significantly between material collected from seven stations for the three species. The results suggest microscale morphological adaptations against drought on the more arid SFS, caused presumably by climatic selection.