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Spores of arbuscular mycorrhizal (AM) fungi were isolated from two heavy-metal polluted soils in France via trap culture with leek (Allium porrum L.). Preliminary identification showed that the predominant spore type of both cultures (P2 and Cd40) belongs to the Glomus mosseae group. Their sensitivity to cadmium was compared to a laboratory reference strain (G. mosseae) by in vitro germination tests with cadmium nitrate solutions at a range of concentrations (0 to 100mg L -1) as well as extracts from a metal-polluted and unpolluted soils. Both cultures of AM fungi from heavy-metal polluted soils were more tolerant to cadmium than the G. mosseae reference strain. The graphically estimated ECs0 was 0.8mg L -1 Cd (concentration added to the test device) for G. mosseae and 7mg L -1 for P2 culture, corresponding to effective Cd concentrations of approximately 50-70 Ixg L 1 and 200-500 Ixg L 1, respectively. The extract of the metal-polluted soil P2 decreased germination of spores from the reference G. mosseae but not from P2 culture. However, the extracts of two unpolluted soils with different physico-chemical characteristics did not affect G. mosseae, whereas germination of P2 spores was markedly decreased in the presence of one of the extracts. These results indicate a potential adaptation of AM fungi to elevated metal concentrations in soil. The tested spores may be considered as metal-tolerant ecotypes. Spore germination results in presence of soil extracts show the difficulty of assessing the ecotoxic effect of metals on AM fungi without considering other soil factors that may interfere in spore germination and hyphal extension.

The weathering of minerals within the rhizosphere has been demonstrated many times; however, only a few studies have been concerned directly with root‐microorganism interactions. This study was conducted to determine the influence of symbiotic (mycorrhizal) and nonsymbiotic microorganisms on rhizospheric weathering of mica. A lysimetric experiment was performed in a greenhouse to study the weathering of a mica (phlogopite) by roots and rhizospheric microorganisms of pine (Pinus sylvestris L.). Pine roots were inoculated or not with an acid‐producing rhizobacteria (Agrobacterium sp.) and an ectomycorrhizal fungus (Laccaria laccata [Scop.: Fr.] Berk. and Broome). In noninoculated pine, rhizospheric phlogopite particles were smaller than control phlogopite particles and partially transformed into vermiculite. Inoculation of pine roots with the bacteria increased cation‐exchange capacity and losses of K from the mica flakes. Losses were attributed to increased production of organic acids in the rhizosphere by the bacteria. Fewer losses of K were observed in pine mycorrhizosphere as monitored by x‐ray diffraction. Electron microscopic observation with a microprobe, however, demonstrated that K losses were greater for the phlogopite particles closely attached to the mycorrhizae. The mycorrhizal effect was attributed to an increase of exchange surface area, rather than to an increase in acidification. Dual inoculation significantly promoted mycorrhizal infection and phlogopite cation‐exchange capacity, compared with inoculation with the bacterium or the fungus alone.

This study was designed to examine saprophytic fungi diversity under different tree species situated in the same ecological context. Further, the link between the diversity and decomposition rate of two broadleaved, two coniferous and two mixed broadleaved-coniferous litter types was targeted. Litter material was decomposed in litter bags for 4 and 24 months to target both early and late stages of the decomposition. Fungal diversity of L and F layers were also investigated as a parallel to the litter bag method. Temperature gradient gel electrophoresis fingerprinting was used to assess fungal diversity in the samples. Mass loss values and organic and nutrient composition of the litter were also measured. The results showed that the species richness was not strongly affected by the change of the tree species. Nevertheless, the community compositions differed within tree species and decomposition stages. The most important shift was found in the mixed litters from the litter bag treatment for both variables. Both mixed litters displayed the highest species richness (13.3 species both) and the most different community composition as compared to pure litters (6.3-10.7 species) after 24 months. The mass loss after 24 months was similar or greater in the mixed litter (70.5% beech-spruce, 76.2% oak-Douglas-fir litter) than in both original pure litter types. This was probably due to higher niche variability and to the synergistic effect of nutrient transfer between litter types. Concerning pure litter, mass loss values were the highest in oak and beech litter (72.8% and 69.8%) compared to spruce and D. fir (59.4% and 66.5%, respectively). That was probably caused by a more favourable microclimate and litter composition in broadleaved than in coniferous plantations. These variables also seemed to be more important to pure litter decomposition rates than were fungal species richness or community structure.

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