Heavy metal tolerance in some ectomycorrhizal fungi

The metal tolerance of isolates of some common ectomycorrhizal fungi of Pin us and Betula spp., collected on heavily metal-polluted sites was compared with that of strains of the same species from non-polluted areas. The strains isolated from carpophores on unpolluted soils were greatly inhibited by the metals, whereas most of the strains derived from polluted soils were strongly tolerant to heavy metals: some strains were still able to grow very well at concentrations of 1000 mu g g(-1) zinc. The mechanisms for zinc (Zn) and copper (Cu) tolerance are completely different, since zinc tolerance does not result in copper tolerance and vice versa. We suppose that ectomycorrhizal fungi are submitted to a selection for metal tolerance in polluted soils. The possible role of tolerant strains in excluding metals from the host plant is discussed.