Impact of dust load and lead (Pb) stress on leaf functioning of urban vegetation

Excessive lead (Pb) in industrial dust increases serious concerns about its potential impact on human health and environment. Urban trees, as a green and cost-effective alternative, are now considered an eco-sustainable tool used to monitor and mitigate this environmental pollution. The present study investigated the effect of dust particles and lead deposition on plant functioning and micromorphology of two common roadside plants, Eucalyptus camaldulensis and Conocarpus lancifolius, in an industrial city, Faisalabad, Pakistan. Tree leaf samples were collected from 20 sites varying in dust exposure intensity. These samples were analyzed for antioxidant enzymes such as superoxidase dismutase (SOD), peroxidases (POD), and catalases (CAT), as well as for proline and protein contents. An increased leave of reactive oxygen species and proline contents in response to increasing dust load and lead tissue lead concentrations across the tested locations suggested the sensitivity of plants to urban dust. This study suggested that C. lancifolius leaves accumulated relatively higher dust particles and lead contents than E. camaldulensis. However, this excessive dust deposition and lead uptake inhibited carbon and protein synthesis in E. camaldulensis and C. lancifolius, as evidenced by relatively lower leaf photosynthesis and protein contents. We also found that the concentration of CAT (4.90 nmol min-1 g-1 protein), SOD (38.42 U mg-1 protein), and POD (2.64 mu mol min-1 g-1 protein) were higher in E. camaldulensis. The results provide experimental support for the hypothesis that genetically rich populations are better adapted to changing conditions and suggest that C. lancifolius is less sensitive to dust load and lead uptake in terms of growth reduction. Regarding lead uptake and dust removal, C. lancifolius performed better as compared to E. camaldulensis. The above findings are helpful in the quantification of services, assessing the diversity, and identification of eco-friendly trees in urban areas. Furthermore, this study will be helpful for the formulation of future tree-planting policies in urban areas.