Impact des métaux lourds sur les interactions plante/ver de terre ...

Partie C : Résultats – Chapitre C-I1. Introductiontel-00486649, version 1 - 26 May 2010Over the past few decades, the mining industry has produced a large amount of acid,metal-rich waste which has often created a serious risk to the soil environment (1). The natureand extent of this contamination is highly variable, depending on the nature of each mine’sore body and its associated geological strata and climate (2). It is, therefore, important tomake an accurate assessment of the availability and toxicity of heavy metals in each pollutedsoil.Phytoextraction is a technology that uses plants to extract metals from contaminatedsoils and accumulate them in harvestable parts which can then be removed from the site (3,4).This appears to be a cost-effective, non-intrusive and environmentally friendly techniquecompared to conventional techniques and promises to be a phytotechnology with greatpotential for solving the problem of soils polluted with metals (5). Improving thephytoextraction process is a primary goal of current research. There are several avenues ofstudy for increasing the efficiency of remediation. (i) Identify new hyperaccumulator specieswith the requisite properties such as high biomass, high metal uptake and ease of propagation.(ii) Increase the biomass of the hyperaccumulator plant by adding fertilizer or using plantgrowth hormones (e.g. IAA, gibberellins or cytokinin), associating them with Plant GrowthPromoting Rhizobacteria (PGPR) (6,7). (iii) Inoculate the soil with a bacterial communityimproving the availability of the metals (8) and/or with Arbuscular Mycorrhizal Fungi (AMF)(9). (iv) Increase the metal content in the plant by the addition of chelating agents such asglycoletherdiamine tetra-acetic acid (EGTA) or NTA (nitrilotriacetic acid) (7,10,11).Little is known about how the relationships between roots, microorganisms and soilfauna in the rhizosphere affect plant growth and metal uptake. Only a few studies have beencarried out into microorganism-assisted metal extraction by plants. Braud et al. (8) showedthat inoculating the soil with free cells of R. metallidurans gave a five-fold increase in Craccumulation in maize shoots and inoculating the soil with immobilized P. aeruginosa cellsgave five-fold and three-fold increases in Cr and Pb uptake, respectively. There have been nostudies on the effects of soil fauna on phytoremediation. Earthworms are importantcomponents of the rhizosphere ecosystem and can significantly increase plant production byimproving soil fertility and nutrient cycling (12), although other interactions (e.g. betweenearthworms and root pathogens or beneficial soil microorganisms) may also affect plants (13).Some earthworms (for example Lumbricus terrestris, Lumbricus rubellus, or Aporrectodea57