Biological filtration to reduce trace elements in woody biomass – BIOFILTREE

Due to wastes, agricultural and industrial activities, large sites highly contaminated by trace elements (TE) are found in France and Canada imposing hazard(s) to environment and human health. Phytoremediation has become an attractive alternative to other clean up technologies due to their relatively low cost, potential effectiveness and the inherently aesthetic nature of using plants to clean up contaminated sites. This project aims at defining and demonstrating integrated bioremediation technologies for the control of TE transfer into harvestable woody biomass. We propose an original implementation of an integrated bioremediation strategy that combines different tree species in an intercropping strategy together with rhizospheric microorganisms, exploiting the complex interactions evolved for the mutual benefit of both organisms, in which plant roots provide habitat, nutrients and exudates to microbial populations, whereas microbes facilitate mineral nutrition of plants.

It is now widely accepted that rhizospheric microorganisms may actively participate to phytoremediation processes, and may be useful in extending the application of phytoremediation to additional TE contaminated sites. Hosting different mycorrhizal types might be of functional importance for plant nutrition and has been shown to contribute to metal tolerance of host plants as fungi can reduce the metal uptake by the plant by sequestration, extracellular precipitation and biosorption to the cell walls. Indeed mycorrhizal fungi play a filtering/sequestering role on plant roots, enhancing root to shoot metal ratio and increasing survival rate in harsh conditions. Moreover, nitrogen fixing species (Frankia) are also good candidates for remediation by phytostabilization due to an improvement in soil properties and the retention of TE in nodulated roots.

The tripartite associations among Frankia (N-fixing bacteria), ECM fungi and Alnus could improve the growth, nitrogen fixation and mineral acquisition (rock solubilization) of Alnus species, but also that of the neighbouring poplar species. Thus, the problem of nutrient limitation of yield in short rotation coppice can be alleviated by microbial retrieval of nitrogen and phosphorus from soil organic material and from atmospheric N.

The main objectives of the proposal are:
i) The original implementation of large-scale phytostabilization field trials based on intercropping poplar and alder short rotation coppices.
ii) The use of microbial symbionts that will reduce transfer of TE in harvestable aboveground parts of trees. Biofiltration analyses of TE transfer to aboveground parts of trees will be performed and mechanisms involved in TE sequestration by fungal cells will be investigated at the physiological and molecular level.
iii) The retrieval of woody biomass in an energetic sector, by combustion or gasification. Moreover another innovative aspect of the project will deal with a detailed study of the technological and economical feasibility of the different tasks.

This project is therefore characterized by the cooperation of foresters and microbiologists, researchers in the field of forest and mycorrhizal genomics and phytoremediation industries to support the development of an improved scheme of phytostabilisation, with the use of woody biomass in an energy path. All steps of the phytostabilization process – from analysis of site pollution, via tree implementation, TE transfer analysis, to the economic use of woody biomass- will be covered and will therefore allow an economical/regulatory assessment to be proposed to future actors of the phytoremediation area.

This French-Canadian bilateral collaboration will allow a mutual sharing of and access to demonstration fields dedicated to phytoremediation, a mutualisation of human resources, biological materials, techniques and methods and a greater effectiveness and relevance in data interpretation and a broader acquisition of scientific data.