Heavy-metal mobilization and uptake by mycorrhizal and nonmycorrhizal willows (Salix x dasyclados)

Ectomycorrhizal fungi have been shown to affect metal transfer from the soil to the host plant, but the use of these fungi for increased phytoextraction of heavy metals has been scarcely investigated. Therefore, a two-factorial pot experiment was conducted with Salix x dasyclados and (1) two contaminated soils with different concentrations of NH4NO3-extractable metals and (2) two strains of the ectomycorrhizal fungus Paxillus involutus (one strain originating from a noncontaminated site-Pax1, and another from a contaminated sitePax2). The inoculation with Pax2 increased the phytoavailability of Cd in the soils. Inoculation with both fungal strains increased the stem and root biomass, but had no effect on metal concentrations in the stems. Decreased Cd and increased Cu concentrations were observed in the roots of inoculated willows. The inoculation with P involutus increased Cd (up to 22%), Zn (up to 48%), and Cu content in the stems. Decreased Pb content (Cu and Pb content were always < 1 mg per plant) occurred in the stems from plants at the soil with the higher concentration of NH4NO3-extractable metals. Contrary to this, in the soil with lower concentrations of NH4NO3-extractable metals, the inoculation had no significant effects on the total uptake of Zn and Cu and even caused decreased Cd (Pax2) and Pb (Pax1) contents in the stems. Strain Pax:2 had higher colonization densities, but the plants had lower mycorrhizal dependencies in the contaminated soils than after inoculation with the strain Pax1. Generally, metal extractability in the soils substantially affected the mycorrhizal dependency and heavy-metal uptake of the willows. We concluded, that the inoculation with P involutus offers an opportunity to particularly increase the phytoextraction of Zn, but the metal extractability and fungal strain effects have to be tested.