Bioaccumulation of trace metals and photosynthetic pigment responses in transplanted lichen Phaeophyscia hispidula (Ach.) Moberg under semi-arid urban conditions in Jaipur, India.

Urban atmospheric contamination by trace metals is a major environmental concern, particularly in rapidly expanding cities located in semi-arid regions. This study evaluated trace metal accumulation and photosynthetic pigment responses in transplanted lichen Phaeophyscia hispidula (Ach.) Moberg exposed along an urban gradient in Jaipur, Rajasthan, India. Lichen thalli collected from a background/reference site in Nahargarh Wildlife Sanctuary were transplanted to ten urban locations and one reference site representing different levels of urban influence and exposed for 90 days during the pre-monsoon season (March-June 2024). Concentrations of six trace metals (Zn, Pb, Cd, Cr, Cu, and Ni) were quantified using inductively coupled plasma mass spectrometry (ICP-MS), while chl a, chl b, total chl, and carotenoids concentrations were measured spectrophotometrically. Urban exposure sites generally exhibited higher trace metal accumulation compared with the reference site, with greater enrichment observed at locations experiencing higher anthropogenic influence. Increased metal accumulation was associated with reductions in chlorophyll (hereafter chl) pigments, whereas carotenoids concentrations showed increasing trends at several exposed sites, indicating possible physiological adjustment under environmental stress. Pearson correlation analysis, regression analysis, principal component analysis (PCA), and hierarchical cluster analysis (HCA) revealed spatial patterns linking metal accumulation with pigment responses. The findings indicate that transplanted P. hispidula can reflect spatial variation in atmospheric trace metal exposure under semi-arid urban conditions. However, interpretation should consider limitations associated with the single-season exposure period, absence of direct instrumental air-quality measurements, and possible influence of additional environmental factors such as dust loading and microclimatic variation. This study provides baseline information on trace metal accumulation and physiological responses of P. hispidula in Jaipur and supports further investigation of lichen transplantation approaches in dryland urban environments.