The effect of air pollution on the morphological traits of the leaves of Platanus orientalis

The study of the response and adaptation of the trees' leaves exposed to air pollutants is a good indicator of plant yield in contaminated environments. In this study, the effect of metal contaminants on changing the morphological traits of platanus orientalis leaves in Chitgar and Azadi Square in Tehran was investigated.

Two areas were selected for sampling. Area one was a low-traffic environment (from the interior space of Chitgar Park) and a high-traffic environment (Azadi Square). In each area, five healthy and disease-free tree base of plantain type (Platanus orientalis) were randomly selected at the shortest distance from the street. Completely healthy leaves were collected from the outermost part of each tree canopy from the street side in the first half of September. The leaves were collected at 10 to 11 am. To ensure that the stomata were open. The leaves were put in wrapped nylons in an ice tank with minimal hand contact and transported to the laboratory in the shortest time. Morphological traits of plantain leaves and stomata were measured. Metal concentration was also measured.

Pb, Hg, Fe, Cu, Cr, Co, Cd, and Ni were more polluted than other metals and their toxicity in Azadi was more than Chitgar. The results of the study indicated that in the presence of heavy metal contaminants in the environment, the leaf length, width, area, fresh and dry weight, and the relative water content decreased while the dent per area unit, vein distribution per blade area, and special area of the leaf increased. As Cu increases, the leaf area decreases and the symptoms of Cholosis appear. The accumulation of cadmium, lead and nickel will reduce the size of Mesophile tissue and epidermal cells. Dry and fresh weight of platanus orientalis leaves in Azadi reduced in comparison to Chitgar. The decrease of dry weight is a complication of cadmium toxicity. Stomatal length, width, and size decreased while stomatal density increased. Stomatal strength, stomatal density, and stomatal size increased in upper leaf area.

By decreasing the contact surface with the pollutant and changing the stomatal size and density, platanus orientalis adjusts gas exchanges with the environment. The occurrence of these morphological adaptations increases the stability of platanus orientalis to the air pollutants stress.