Metal bioaccumulation and physiological responses of Arctic lichens under climate change and pollution

Metal contamination and climate change, driven by global warming, are influencing the release and bioavailability of trace and heavy metals in the Arctic. Lichens, particularly Flavocetraria nivalis and Cladonia mitis, serve as effective bioindicators of environmental change. This study aimed to: (1) compare metal content in lichens collected in 1985 and 2023 from the Hornsund region; (2) assess metal concentrations in soils and lichen thalli from two Svalbard regions (Adventfjorden and Hornsund); and (3) explore relationships between usnic acid, metal bioaccumulation, and photosynthetic activity (Fv/Fm). A comparison between 1985 and 2023 samples of lichen thalli revealed an increase in several metals, including Mn (from 9 to 53 mg $kg^{−1}$ in F. nivalis and from 9 to 22 mg $kg^{−1}$ in Cl. mitis), as well as Ni, Co, and Zn. Cr content in both species exceeded typical lichen tolerance thresholds (>10 mg $kg^{−1}$). While Cd content decreased in both species, Pb increased only in F. nivalis (from 3.76 to 6.05 mg $kg^{−1}$). In F. nivalis usnic acid content increased significantly (from 15 to 60 mg $g^{−1}$). Soil samples from Hornsund contained higher overall metal loads than those from Adventfjorden. F. nivalis exhibited bioaccumulation factor (BAF) > 1 for a greater number of metals compared to Cl. mitis, indicating higher uptake potential. Usnic acid in F.nivalis showed negative correlations with photosynthetic activity (Fv/Fm, r = –0.55) and Cd, Cu, and Zn. In Cl. mitis, usnic acid was positively correlated with Fv/Fm. These findings demonstrate species-specific physiological and biochemical responses to metal exposure, highlight the role of usnic acid as a potential biomarker of contamination, and emphasize the need for continued monitoring of metal pollution and lichen adaptation in Arctic ecosystems.