The effects of nickel and copper on the axenic growth of ectomycorrhizal fungi

Isolates of several ectomycorrhizal fungi, some from a Cu- and Ni-contaminated smelter site near Sudbury, Ont., and some from an uncontaminated site, were grown on solid media containing 25 or 100 mg nickel/L, or 25 or 100 mg copper/L. The influence of the metals on lag time prior to the commencement of growth, on the maximum increase in colony diameter, and on the final colony dry weight was determined. Isolates from the metal-contaminated site did not outperform those from the uncontaminated site on any of the metal-amended media. In a second experiment, isolates of Laccaria proximo, Lactarius hibbardae, Lactarius rufus, and Scleroderma flavidum were grown in liquid media containing 2 or 5 mg Ni/L or 4 mg Cu/L. These fungi have previously been shown to vary in their effect on the metal tolerance of Betula papyrifera, at these concentrations. The axenic growth of the fungi in the presence of Ni showed no relationship to their effect on the birch seedlings. In general, the fungi that were least tolerant to Cu in liquid culture, Lactarius rufus and Laccaria proximo, were the same ones that proved most detrimental to the birch grown in the presence of Cu. These results indicate that axenic screening tests will not necessarily select fungi that will increase host metal tolerance.