Contribution of Ectomycorrhizal Fungi to Cadmium Uptake of Poplars and Willows from a Heavily Polluted Soil

Phytoextraction has been proposed in recent years as an environmentally and cost-efficient treatment technique for the remediation of heavy-metal contaminated sites. In particular, plants that are fast growing, metal accumulating, and economically interesting, such as sunflowers or trees, recently became more important in research on phytoextraction. Heavy metal uptake of trees can be strongly influenced by ectomycorrhizal fungi. We investigated the possibility of enhancing phytoextraction of Cd by willows (Salix viminalis) and poplars (Populus canadensis) in association with three well known ectomycorrhizal fungi (Hebeloma crustuliniforme, Paxillus involutus and Pisolithus tinctorius). A pot experiment was conducted using Cd polluted soil from a contaminated site. Four replicates of each combination of fungus and tree species, and controls without fungal inoculum, were set up. After a growth period of 11 weeks, yields and Cd concentrations in roots, stems, and leaves were measured. In addition, the total Cd uptake, the transfer to roots, and the translocation to stems and leaves were calculated. The association of P. canadensis with P. involutus led to a highly significant increase of Cd concentrations, in particular in the leaves, which contained 2.74 ± 0.34 mg Cd per kg dry matter. Compared to the control this is an enhancement of nearly 100%. The fungi also significantly enhanced the translocation from the roots to the leaves, leading to a concentration ratio (leaves/roots) of 0.32 ± 0.06 compared to 0.20 ± 0.02 of the control plants. Additionally, P. involutus significantly enhanced the total Cd extraction by P. canadensis. Similar effects were not observed by other fungi or in association with S. viminalis.