Effect of zinc and copper on cultivable populations of soil fungi with special reference to entomopathogenic fungi

The effect of copper and zinc on cultivable soil fungi populations was investigated in a laboratory experiment. Samples of four different soils (arable sandy soil and loam clay; forest sandy soil and forest peat) were collected from sites located in Vilnius district, Lithuania. Metals’ effect was elaborated by addition of metal salts (CuSO4 and ZnSO4) at appropriate concentrations into the growth medium (Czapek's agar) and evaluating cultivable fungi abundance and species diversity changes. Zinc or copper salt was added to the medium after its sterilization; zinc concentration varied from 0.05 to 0.20 M (by 0.05 M concentration range) and copper concentration – from 0.5 to 3.0 mM (by 0.15 mM concentration range). At elevated metal salt concentrations, the abundance of cultivable fungi decreased with a marked elimination of some fungi species as compared with a control medium (without metal addition) fungi cultures. Irrespective of a fungi community structure in different type soils, Cu was a stronger inhibitor of soil fungi population abundance than Zn, however, both metals showed a comparable effect on the fungi species diversity. The most resistant fungi belonged to common insect pathogens (Beuveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Isaria spp.), which dominated comprising up to 90% of all recovered from the soils isolates, due to the metal salt concentration.