Evaluation of the air pollution tolerance index of ornamentals growing in an industrial area compared to a less polluted area

The aim of this study was to compare the ability to absorb various air pollutants of common roadside ornamental plants growing in an industrial center of Faisalabad, Pakistan, with that of ornamental plants growing at University of Agriculture, Main Campus, Faisalabad, Pakistan. Leaf samples of 17 plant species were collected from both locations and four physiological and biochemical parameters, i.e., relative water content, leaf extract pH, total chlorophyll content, and ascorbic acid content, were assessed. The air pollution tolerance index (APTI) was calculated from the obtained values. The results demonstrated the substantial impact of pollutants on the APTI; most of the tested plants grown at the industrial site had a higher APTI than those grown on the campus. Among the tested ornamental plant species, Hibiscus rosa-sinensis (9.8) had the highest APTI value, which was similar to Alstonia scholaris (9.4), Bougainvillea spectabilis (9.6), Morus nigra (9.5), Murraya exotica (9.0), and Nerium oleander (9.0) at the industrial location, while at the campus, B. spectabilis (7.2) had the highest APTI value, which was similar to Ficus benjamina (6.5), H. rosa-sinensis (6.6), Lagerstroemia indica (6.6), and Nerium oleander (6.5). However, Duranta repens, Melia azedarach, and Tecoma stans had the lowest APTI values at both locations, with values of 6.6, 7.5, and 7.7 at the industrial location and 5.5, 5.5, and 5.6 at the campus, respectively. Moreover, Alstonia scholaris, H. rosa-sinensis, and M. nigra had the highest relative difference in APTI between the two sites, with differences of 3.7, 3.2, and 3.2, respectively. In summary, among 17 ornamental species, A. scholaris, B. spectabilis, H. rosa-sinensis, L. indica, M. nigra, and N. oleander are the most desirable for planting around industrial zones on the basis of APTI and can be used as bio-monitors of environmental pollutants in industrial zones.