DIFFERENTIAL TOLERANCE TO CD AND ZN OF ARBUSCULAR MYCORRHIZAL (AM) FUNGAL SPORES ISOLATED FROM HEAVY METAL-POLLUTED AND UNPOLLUTED SOILS

Spores of arbuscular mycorrhizal fungi were isolated from two soils of field trials at INRA-Bordeaux (France) polluted by long-term applicat ion of a zinc-polluted sewage sludge (S2 soil) or treated with cadmium nitrate (Cd40 soil) and from corresponding unpolluted soils (F and Cd 0 soils). These AM fungi were tested for their tolerance to Cd and Zn added as salt solutions with increasing concentrations (0 to 10 mg L(- 1)) in a simple spore germination device. According to preliminary ide ntification the predominant species in S2 and F cultures was Glomus mo sseae, whereas Cd40 and Cd0 cultures contained a mixture of at least G . mosseae and G. etunicatum. Germination of Cd40 spores was more toler ant to Cd and Zn than for Cd0 spores, with EC(50) values of 73 and 158 mu mol L(-1) added Cd and Zn corresponding to approximately 10 and 13 mu mol L(-1) remaining in solution in the device. The S2 spores from the sludge contaminated soil were more tolerant to Zn (EC(50) = 87 mu mol L(-1)), but not to Cd (EC(50) = 7.5 mu mol L(-1)), than the spores from the farmyard manure-treated F soil (EC(50) = 38 and 8.8 mu mol L (-1), respectively). Thus, S2 culture exhibited a specific tolerance t o Zn, which was lower than the unspecific tolerance of Cd40 culture to both Cd and Zn, despite the much higher Zn availability in S2 soil. T hese results indicate that AM fungi from different soils may differ in their metal susceptibility and that both metal specific and unspecifi c tolerance mechanisms may be selected in metal polluted soils.