Does the lichen mat alleviate the effects of wet deposited nickel on soil microorganisms and Scots pine (Pinus sylvestris L.) seedlings?

A field experiment was conducted in a dry heath forest dominated by Scots p ine ( Pinus sylvestris L.) and a mat-forming lichen (Cladina stellaris (Opi z) Brodo) to assess the effect of wet-deposited nickel (Ni) on pine seedlin gs and soil microorganisms, and to explore whether an intact lichen mat cou ld act as a buffer against heavy metal deposits. Pine seedlings were plante d in quadrats covered by a natural lichen layer and in quadrats from which the lichen layer had been completely removed. The quadrats were exposed to four levels of Ni deposition: 0 (i.e., distilled water), 10, 100 and 1000 m g m(-2) year(-1) in two growing seasons. Increasing Ni deposition led to an increase in the Ni content of the needles, roots and the soil organic laye r. The lichen mat reduced Ni flow to the organic soil layer, but had no sig nificant, reducing effect on needle or root Ni concentration. The most seve re Ni treatment had detrimental effects on seedling growth and increased pe roxidase activity in the previous years needles. Removal of the lichen laye r did not increase susceptibility of seedlings to Ni. Values of maximal car bon use efficiency (Max) and metabolic quotient (qCO(2)) of the soil microo rganisms indicated protective value of the lichen mat to soil microorganism s at the highest Ni treatment. Skimming per se decreased basal respiration, qCO(2) and concentrations of potassium in the soil and also increased the lag period of the microorganisms as a response to in situ substrate additio n.