Xeromorphic Features of the Leaves of Liriodendron Tulipifera L. (Magnoliaceae) in the Arid Climate of Central Asia

High irradiance of a habitat in arid areas is usually associated with high temperature and dry air, which can cause water deficiency in plants. The Tulip tree (Liriodendron tulipifera) is a light-loving mesophytic species. This study showed that L. tulipifera forms shade or sun leaves depending on the light conditions. Some xeromorphic features were found in leaves of the trees in illuminated habitats. These sun leaves are smaller, denser, and thicker, with smaller epidermal cells and a thick cuticle; the spongy parenchyma consists of a larger number of rows of small cells; the cells of the columnar parenchyma are larger than the shade leaves. The sun leaf contains more total chlorophyll (by 20–30%), and the guard cells of the stomata of the sun leaf contain chloroplasts. The increased concentration of chlorophyll probably maintains the energy balance in the conditions of inhibited photosynthesis under high illumination and temperature. Decreased sizes of the sun leaf and epidermis cells, thickening of the cuticle and cell wall of epidermal cells, sunken stomata, compact mesophyll with small intercellular spaces, and multirow spongy parenchyma protect from overheating and passive loss of water and can be considered as xeromorphic features. Large numerous stomata and vascular bundles contribute to effective cooling of the surface by transpiration at high temperatures under sufficient water supply. Thus, the leaves of L. tulipifera have an ecological plasticity in relation to illumination and temperature, which contributed to the acclimation of the species to the habitat conditions in arid climates.