Phytoremediation of Metal Contaminated Soil Using Willow: Exploiting Plant-Associated Bacteria to Improve Biomass Production and Metal Uptake

Abstract

Short rotation coppice (SRC) of willow and poplar is proposed for economic valorization and concurrently as remediation strategy for metal contaminated land in northeast-Belgium. However, metal phytoextraction appears insufficient to effectuate rapid reduction of soil metal contents. To increase both biomass production and metal accumulation of SRC, two strategies are proposed: (i) in situ selection of the best performing clones and (ii) bioaugmentation of these clones with beneficial plant-associated bacteria. Based on field data, two experimental willow clones, a Salix viminalis and a Salix alba x alba clone, were selected. Compared to the best performing commercial clones, considerable increases in stem metal extraction were achieved (up to 74% for Cd and 91% for Zn). From the selected clones, plant-associated bacteria were isolated and identified. All strains were subsequently screened for their plant growth-promoting and metal uptake enhancing traits. Five strains were selected for a greenhouse inoculation experiment with the selected clones planted in Cd-Zn-Pb contaminated soil. Extraction potential tended to increase after inoculation of S. viminalis plants with a Rahnella sp. strain due to a significantly increased twig biomass. However, although bacterial strains showing beneficial traits in vitro were used for inoculation, increments in extraction potential were not always observed.

Keywords::

• phytoextraction
• Salix
• plant-associated bacteria
• inoculation
• cadmium
• zinc

Acknowledgments

This research was funded by the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) for J.J. and by the Fund for Scientific Research Flanders (FWO Vlaanderen), Ph.D. grant for S.C. and post-doc grant for N.W.. This work has been financially supported by the UHasselt Methusalem project 08M03VGRJ and by the European Commission under the Seventh Framework Program for Research (FP7-KBBE-266124, GREENLAND). We thank Wim De Clercq for providing Salix biomass and Thomas Neyens from I-BIOSTAT (UHasselt) for support with statistics.