Impact of wet deposited nickel on the cation content of a mat-forming lichen Cladina stellaris

The impact of experimentally sprayed aqueous nickel solution on the concent rations of potassium, calcium, magnesium and nickel in three horizontal str ata (top, 0-20 mm; middle, 20-40 mm; and base, 40-60 mm) of the cushion-for ming lichen Cladina stellaris was investigated. The experimental nickel dep osition range used corresponded with that from the pristine forests of the Finnish border to polluted industrial sites of Russian Kola Peninsula (0-10 00 mg Ni2+ m(-2) year(-1)). The lichen mat retained ca. 31-66% of the nicke l deposited during two growing seasons and the relative retention efficienc y was highest at the low deposition end. The concentrations of cations in l ichen thalli were significantly reduced only after the highest nickel depos ition. Furthermore, the separate horizontal strata responded differently to nickel exposure indicating that the cation exchange sites of the top strat um were not completely saturated by nickel even after the most severe treat ment. However, nickel deposited in high doses caused considerable reduction in potassium concentration indicating damage to cell membranes. Episodical ly deposited high concentrations of nickel can probably affect membrane int egrity before detectable changes in total concentrations of cations in the lichen thallus take place. Thus, ratios of total concentrations of cations in the lichen thallus are fairly insensitive to nickel deposition, which re duces the risk of compounding effects when the ratios are used to indicate long-term acid deposition in areas with multiple pollution problems such as Kola Peninsula. (C) 2000 Elsevier Science B.V. All rights reserved.