Plants as Indicators of Air Pollution: an Indian Experience

Indicator plants have been used to survey the effects of air pollution from a single source or cluster of sources on horticultural, agricultural and forestry crops or on natural vegetation. However there are many tree species for which studies are not available in the literature. Tree species are exposed to a variety of pollutants in field conditions varying in either high or low concentrations. Most of the studies ignored the possible impact of pollutants in low concentrations. Trees are continuously exposed to air pollution in the field, but in experimental studies, plants are exposed to single air pollutant for shorter duration, so the responses observed during experimental studies are difficult to extrapolate to field conditions. Air Pollution Tolerance Index (APTI) is normally used for the relative susceptibility of trees species toward air pollutants. APTI uses only four parameters: ascorbic acid, total chlorophyll, leaf extract PH and relative water content. APTI gives a broad idea of pollution tolerance of plants. However based on the APTI, some of the plants are identified in decreasing order of the air pollution tolerance which is as follows: Mangifera indica > Dalbergia sissoo > Cassia fistula > Azadirachta indica > Polyalthia longifolia > Ficus religiosa> Ficus benghalensis.