-National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440020, India

Vehicular pollution is one of the major stressors along the high-traffic urban roads that plants need to cope up to flourish. Alteration in pigment content is a prudent response of most of the plants under environmental stresses. Effect on pigment system is one of the major indicators of metabolic status of plant, and magnitude of stress effect on the constituent components of the pigment system depends on various factors. Therefore, quantification of stress effect on the pigment system could be a useful tool for determining vulnerability/endurance of the species to the stressful ambience. To determine suitability of plant species in polluted niche, often Air Pollution Tolerance Index (APTI) is used, which takes account of total chlorophyll content as the representation of pigment system. In this study, in addition to total chlorophyll content, chlorophyll a/b ratio and carotenoids content were assessed in 24 commonly planted tree species growing around crowded urban roads, and compared with their counterparts in less polluted non-urban environment. It was found that air pollution effects on chlorophyll a:b ratio, carotenoids content in addition to total chlorophyll content, and response of pigment components were different amongst species. Most of the species showed no change in total chlorophyll content over control, but remarkable increase in chlorophyll a/b ratio coupled with reduction in carotenoids content. Five different patterns of responses were observed thus the species were categorised accordingly. The pattern of response is found to have pronounced effect on stress tolerance and susceptibility of species. Tolerance or susceptibility of pigment system to air pollution is cumulative effect of response of chlorophyll a, chlorophyll b and carotenoids. It is inferred that these pigment components are important parameters to be taken into account for assessing suitability of plant species for air-polluted environment.