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Ultrastructural Responses of the LichenBryoria fuscescensto Simulated Acid Rain and Heavy Metal Deposition

Abstract Effects of simulated acid rain and heavy metal deposition on the ultrastructure of the lichenBryoria fuscescens(Gyeln.) Brodo and Hawksw. were examined in a field study conducted in northern Finland. Lichens were exposed to simulated rain containing two levels of a mixture of copper (Cu2+) and nickel (Ni2+) ions alone or in combination with acid rain (H2SO4) at pH 3 over 2 months in addition to ambient rainfall. The algal and fungal components responded differently to pH and there was an interaction with metal toxicity. The algal partner was the most sensitive to acid rain and heavy metal combinations and had more degenerate cells than the fungal partner. Damage was apparent in chloroplasts and mitochondria, where thylakoid and mitochondrial cristae were swollen. The fungal partner was the more sensitive to high concentrations of metal ions in the absence of acidity, suggesting an ameliorating interaction between the metals and acidity. For algae, critical metal concentrations in the thallus were >50 μg g−1for Cu and >7 μg g−1for Ni in the presence of acidity, and >20 μ g g−1for Ni in the absence of acidity. Detrimental effects of heavy metals on fungal ultrastructure were seen when thallus metal concentrations exceeded 400 μg g−1for Cu and 100 μg g−1d. wt for Ni. The results suggest that acid wet deposition containing metal ions may reduce survival of lichens in northern environments.