Heavy metal accumulation in needles of Pinus eldarica and leaves anatomical responses to the urban pollution

Atmospheric heavy metals pollutions affect needles anatomical properties of coniferous trees. The present study investigated the accumulation of cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), and chromium (Cr) on needles of Pinus eldarica and leaves anatomical responses to urban pollutions in downtown of Tehran Mega city (Keshavarz Boulevard, henceforth KB) as the highest polluted area and in the Chitgar Forest Park (hereafter CFP), west of Tehran, as the lowest. To achieve this, needles were collected in 2015, summer season and structural characteristics needles, i.e., leaf surface, stomatal density, width and length of stomata, as well as epidermis and cuticle thickness, were measured. The results exhibited that the concentrations of Cd, Pb, Cr, and Cu in KB were 0.51, 8.41, 0.51 and 4.2 µg/g, respectively, which were more than those in the CFP (0.05, 2.18, 0.1 and 3.8 µg/g, respectively). No significant difference, however, was detected between KB and CFP in terms of Zn and Ni concentrations. Leaf area in KB (0.132 cm²) was less than that in CFP (0.137 cm²). Stomatal density and length in KB were 92 per mm² and 20.9 µm, respectively, against those of CFP (112 per mm² and 24.13 µm). Upper and lower epidermises in KB (5.3, 5.4 µm, respectively) was significantly thinner than those in CFP (6.2, 6.1 µm). The observed changes in anatomical properties are physiological and structural strategies of P. eldarica leaves against stress tolerance induced by urban pollutions. P. eldarica is anatomically sensitive to the pollutants concentrations measured in this study and needle leaves structural characteristics change to adapt to the pollution stress.