Differences in Norway maple leaf morphology and anatomy among polluted (Belgrade city parks) and unpolluted (Maljen Mt.) landscapes

Norway maple (Acer platanoides L.) is often used for urban landscaping because it is considered to be tolerant to different ecological conditions. This study examined leaf anatomy and morphology, and leaf damage symptoms (using the light and SEM microscopy) of maple tree growing in three Belgrade city parks (high polluted sites: park “Hall Pioneer” and Botanical garden “Jevremovac” within City industrial zone, and low polluted Kalemegdan park), and control site (unpolluted) at Maljen Mt. during a two-year period. Microscopic measures included thickness of leaves, upper and lower epidermis, palisade and spongy mesophyll and stomatal density. Differences in leaf attributes varied significantly among sites. Leaves in parks within industrial zone were thicker (with changes most expressed by the thickening of palisade mesophyll), smaller, heavier and more voluminous from the control ones. Leaf damage were noted only in the urban zone, expressed in form of light to dark colour chloroses, and reddish-brown marginal necroses related to toxic effect of elevated concentrations of particulate matter, SO2, and Pb, Zn and Ni in city air. Damage ranged from lesions to the last stadium of necrosis of whole mesophyll. SEM microscopy indicated erosive damage of the cuticle and stomata. We concluded that the sensitivity to air pollution of A. platanoides leaves is related to its leaf structure, low leaf volume and large intercellular spaces. In the same time, the leaf structural change (due thickening of mesophyll and increasing of leaf volume) follows the course of developing xeromorphic adaptations to the stressful conditions of urban environment