CD-TOLERANT ARBUSCULAR MYCORRHIZAL (AM) FUNGI FROM HEAVY-METAL POLLUTED SOILS

Spores of arbuscular mycorrhizal (AM) fungi were isolated from two hea vy-metal polluted soils in France via trap culture with leek (Allium p orrum L.). Preliminary identification showed that the predominant spor e type of both cultures (P2 and Cd40) belongs to the Glomus mosseae gr oup. Their sensitivity to cadmium was compared to a laboratory referen ce strain (G. mosseae) by in vitro germination tests with cadmium nitr ate solutions at a range of concentrations (0 to 100 mg L-1) as well a s extracts from a metal-polluted and unpolluted soils. Both cultures o f AM fungi from heavy-metal polluted soils were more tolerant to cadmi um than the G. mosseae reference strain. The graphically estimated EC5 0 was 0.8 mg L-1 Cd (concentration added to the test device) for G. mo sseae and 7 mg L-1 for P2 culture, corresponding to effective Cd conce ntrations of approximately 50-70 mug L-1 and 200-500 mug L-1, respecti vely. The extract of the metal-polluted soil P2 decreased germination of spores from the reference G. mosseae but not from P2 culture. Howev er, the extracts of two unpolluted soils with different physico-chemic al characteristics did not affect G. mosseae, whereas germination of P 2 spores was markedly decreased in the presence of one of the extracts . These results indicate a potential adaptation of AM fungi to elevate d metal concentrations in soil. The tested spores may be considered as metal-tolerant ecotypes. Spore germination results in presence of soi l extracts show the difficulty of assessing the ecotoxic effect of met als on AM fungi without considering other soil factors that may interf ere in spore germination and hyphal extension.