Air Pollution Mitigation Potential of Dominant Landscape Plants of an Urban Ecosystem (Lahore City) of Pakistan: An Air Pollution Tolerance Index (APTI) Assessment

Lahore, the second largest city of Pakistan with higher population and large industrial zones, is under tremendous environmental stress of increasing air pollution. Roadside plants can mitigate increasing pollution rate by serving as a natural sink. This research work was designed to evaluate the role of roadside plantation in pollution mitigation in an urban ecosystem of Lahore. In this urban ecosystem, three busiest roadsides i.e., Zafar Ali Road, Canal Road and Jail Road with heavy traffic flow and commonness of plants were selected as sampling sites. Air Pollution Tolerance Index (APTI) of the selected plants was calculated through chlorophyll content (mg/g), ascorbic acid content (mg/g), relative water content (%) and pH. At control sites, ascorbic acid ranges from 3.11 & PLUSMN;0.21 (Cosmos sulphureus) to 1.18 & PLUSMN;0.08 (Tabarnaemontana divaricata) while at polluted sites, it was found to range from 2.95 & PLUSMN;0.09 (Cosmos sulphureus) to 1.03 & PLUSMN;0.08 (Tabarnaemontana divaricata). Chlorophyll content ranged from 37.00 & PLUSMN;1.11 (Ficus religiosa) to 5.28 & PLUSMN;1.22 (Hibiscus rosa sinensis) at control sites, while at polluted sites, it ranged from 29.09 & PLUSMN;1.15 (Ficus reliogiosa) to 5.56 & PLUSMN;0.95 (Tabarnaemontana divaricata). At control sites, relative water content ranged from 198.76 & PLUSMN;2.45 (Catharanthus roseus) to 10.02 & PLUSMN;1.95 (Tabarnaemontana divaricata) while at polluted sites, it was found to range from 192.40 & PLUSMN;2.11 (Catharanthus roseus) to 9.50 & PLUSMN;1.18 (Tabarnaemontana divaricata). At control sites pH value ranged from 6.69 & PLUSMN;0.21 (Catharanthus roseus) to 5.04 & PLUSMN; 0.45 (Alstonia scholaris). At polluted sites, it ranged from 6.69 & PLUSMN;0.21 (Catharanthus roseus) to 5.42 & PLUSMN;0.48 (Alstonia scholaris). At control sites, APTI value varies from 28.45 & PLUSMN;0.21 (Catharanthus roseus) to 2.59 & PLUSMN;0.11 (Tabarnaemontana divaricata). While at polluted sites, APTI value ranges from 27.57 & PLUSMN;1.45 (Catharanthus roseus) to 2.18 & PLUSMN;1.33 (Tabarnaemontana divaricata). Calculated APTI values were correlated with ascorbic acid, chlorophyll, %relative water content and pH. Highly positive correlation was found between APTI and ascorbic acid with R2 = 0.9183. While slightly positive correlation of APTI with chlorophyll and relative water content (R2 = 0.3779 and 0.336 respectively) was found. This indicates towards their participation in strengthening plants' defense mechanism. This research work followed by statistical analyses evaluates the tolerance level of plants towards air pollution. This evaluation paves the way in screening out the tolerant plants for pollution abatement. In this research work, Catharanthus roseus and Cosmos sulphureus were found tolerant to air pollution having high APTI values while Helianthus annuus, Ficus benjamina, Ficus religiosa, Hibiscus rosa-sinensis, Robinia pseudoacacia, Alstonia scholaris and Tabarnaemontana divaricata was found sensitive to the air pollution.