Phytoextraction of nickel and rhizosphere microbial communities under mono- or multispecies hyperaccumulator plant cover in a serpentine soil
Marie Rue, Jessica Vallance, Guillaume Echevarria, Patrice Rey and Emile Benizri
Laboratoire Sols et Environnement, Université de Lorraine, UMR 1120, 2 Avenue de la Forêt de Haye, TSA 40602, Vandoeuvre-lèss-Nancy, F-54518, France.
The efficiency of nickel (Ni) phytoextraction by hyperaccumulating Brassicaceae was compared in two types of covers, namely, monoculture or mixed culture. The selected species were from the Pindus Mountains (Greece), including Alyssum murale, Noccaea tymphaea, Leptoplax emarginata and Bornmuellera tymphaea. After 4 months of culture in mesocosms using ultramafic soil (Ni = 1480 mg kg-1), plant biomass yield and Ni concentrations in shoots and roots were recorded for each of six treatments (mixed-culture cover, four monoculture covers and unplanted soil). Microbial biomass carbon, the size of the cultivable rhizosphere bacterial community and its phenotypic structure (Biolog EcoPlates™), bacterial and fungal genetic structure (SSCP), as well as the potential production of auxin compounds, were also evaluated. Moreover, measurements of various microbial enzymes were performed. The biomass and shoot Ni concentration (albeit not significant) of B. tymphaea increased in co-cropping system. A slight acidification of the soil occurred and a strong correlation between pH and the size of the bacterial community was also observed. No significant change in enzyme activity was observed among the cover types, except in the case of arylsulfatase. The phenotypic structure of the bacterial communities and the bacterial and fungal genetic structures appeared to be specific to the type of cover, although the size of the culturable bacterial community did not show variation among treatments. Therefore, on the basis of the bioaccumulation coefficient and the translocation factor, our results showed that B. tympheae, and to a lesser extent N. tympheae, were the two species with the greatest Ni phytoextraction potential in co-culture systems.
Keywords: Biolog™, hyperaccumulating plants, molecular fingerprinting, rhizobacteria.