Zoning of Leaf Chlorophyll Content of Tree Species (A Case study in Malayer City, Iran): An Indicator to Investigate Air Pollution in Urban Environments

Air pollution is currently one of the most important environmental issues. The most common effect of air pollution on plants is the gradual decomposition of chlorophyll and leaf yellowing, which may result in the reduction of photosynthetic capacity. This study aimed to investigate the effect of air pollution on the chlorophyll content and zonation of leaf chlorophyll content of two tree species in Malayer city, Iran.

Samples were collected from two tree species, namely, Platanus orientalis and Robinia pseudoacacia in different parts of Malayer city, Iran (clean and polluted areas), each with three replications. The concentration of pigments in the leaves was measured by the Lichtenthaler (1987) method, which is the modified Arnon method (1949), at 663 and 645 nm wavelengths, absorbance being measured using a spectrophotometer.

Data analysis showed that the a, b and total chlorophyll contents in the acacia tree species in the southern parts (southwest) of the study area reached their maximums, while their contents were lowest in the eastern and north-western parts and low to medium in the central parts of the study area. On the other hand, as regards the sycamore species, in the eastern and north-western parts of the study area the a, b, and total chlorophyll contents were the highest and reached their minimums in the south-western parts. However, as in the case of the acacia species, in the central parts of the study area the contents of the tree chlorophylls were low to medium.

The results of this study show that the a, b and total leaf chlorophyll contents of the two acacia and plantain species were higher in the polluted areas as compared to those in clean areas. On this basis, it can be said that a higher physiological index, such as an increased chlorophyll content, indicates the plant's response for resistance to air pollutants.