No abstract

Woody plant species that produce high biomass have been proposed for use in phytoremediation technology. We investigated the accumulation of cadmium (Cd) and zinc (Zn) in Salix babylonica, S. caprea, S. dasyclados, S. matsudana × alba, S. purpurea, S. smithiana, Populus tremula, and P. nigra clones grown in a pot experiment on a Calcaric and a Eutric Cambisol (pH 7.2 and 6.4) of different levels of contamination (total metal concentrations in mg kg–1 in soil A: 32.7 Cd, 1760 Zn; soil B: 4.34 Cd, 220 Zn). Generally, the tested clones tolerated large metal concentrations in soils and had larger Cd and Zn concentrations in leaves compared to the roots. The largest Cd concentrations in leaves were found in two clones of S. smithiana (440 mg kg–1 on soil A; 70 mg kg–1 on soil B). One of the S. smithiana clones had also the largest Zn concentrations (870 mg kg–1) on soil B but accumulated slightly less Zn than a S. matsudana × alba clone (2430 mg kg–1) on soil A. The Cd concentrations in leaves of both S. smithiana clones on soil A are the largest ever reported for soil‐grown willows. The bioconcentration factors of the best performing clone reached 15.9 for Cd and 3.93 for Zn on the less contaminated soil B. Also based on the metal contents in leaves, this clone was identified as the most promising for phytoextraction. The metal concentrations in leaves observed in the pot experiment do not reflect those found in a previous hydroponic study and the leaf‐to‐root ratios are clearly underestimated in hydroponic conditions. This demonstrates the need for testing candidates for phytoextraction crops on soils rather than in hydroponics. Our data also show that the phytoextraction potential should be tested on different soils to avoid misleading conclusions.

We conducted a pot experiment to evaluate the Cd and Zn accumulation in leaves and roots of Salix smithiana (BOKU-03DE-001) and S. caprea (BOKU-01AT-004) clones grown on a metal-contaminated soil as affected by native microbes extracted from the same experimental soil, and the fungus Cadophora finlandica. Plant biomass production of S. smithiana was decreased in all the treatments compared to the sterilized control. In contrast, S. caprea grew best on the non-sterilized soil. Similar effects were observed for plant Zn and Cd contents. Microbial treatments affected metal accumulation differently in the two Salix species. The effects of the microbial treatments on biomass and metal content of leaves were not related to the degree of mycorrhization. A comparison with literature data suggests that the plant response to microbial inoculation in terms of metal accumulation may depend on the plant-internal metal concentration. Our findings also illustrate a difficulty of successful rhizosphere management using metal-tolerant microbial isolates to further enhance the phytoextraction process.