PJB-2024-1514
Impacts of air pollution on trees growing by the roadside of Karachi with respect to their tolerance characteristics
S. Shahid Shaukat, Moazzam Ali Khan and Afsheen Khan
Abstract
An air pollution tolerance index (APTI) proposed by earlier workers is often employed by environmentalists or ecologists to investigate the relative susceptibility of plants to air pollution in mega cities. The APTI was estimated by determining ascorbic acid, total chlorophyll content of leaves, pH of leaf extract and relative water content (%). In the current investigation, this index was employed to evaluate the susceptibility/ tolerance of ten common tree species growing in a polluted site (Guru Mundar area) of Karachi city and relatively unpolluted habitat (Karachi University Campus). Ascorbic acid content, pH of leaf extract and relative water content were found elevated in polluted site over the unpolluted habitat, whereas, total chlorophyll content of leaves was invariably lesser at polluted site. In addition, to the above four parameters we also examined free amino acid content of leaves and the percentage of clogged and partially clogged stomata of the preferred species from the same areas. In general, ascorbic acid, leaf extract, pH and the relative water content of leaves were high in the polluted habitat compared to unpolluted sites, whereas, total chlorophyll content of leaves was lesser at polluted site for almost all the species examined. Tree species with a high APTI value were regarded as tolerant. Tolerant species included Azadirachta indica, Ficus benghalensis, Ficus religiosa, Conocarpus erectus and Peltophorum pterocarpum as indicated by greater magnitude of APTI under polluted regime. Three species including Albizia lebbeck, Guaicum officinale and Polyalthia longifolia were found sensitive to air pollution. Delonix regia did not differ with respect to APTI for polluted and unpolluted situations. The percentage of clogged and partially clogged stomata was in general higher in the polluted site compared to unpolluted habitat. Remarkably, the levels of free amino acid of all species were found accentuated in the polluted site compared to unpolluted habitat. Presumably, an improved APTI can be achieved if the levels of free amino acids and percentage of clogged and partially clogged stomata can be included in the computation of APTI. It is suggested that green belts in the city and its suburbs and developing industrial and residential areas can be planted with trees species having high APTI. This would not only beautify the city but such trees positively act to clean the air and serve as sinks for varied air pollutants leading to better human health
To Cite this article:
Shaukat, S.S., M.A. Khan and A. Khan. 2024. Impacts of air pollution on trees growing by the roadside of Karachi with respect to their tolerance characteristics. Pak. J. Bot., 56(2): DOI: http://dx.doi.org/10.30848/PJB2024-2(14)
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