Occurrence of mycorrhizal symbioses in the metal-rich lateritic soils of the Koniambo Massif, New Caledonia.

The occurrence of arbuscular mycorrhiza (AM) was surveyed in ten endemic plant species of the Koniambo Massif (New Caledonia) and associated metal-enriched ultramafic soils along a topographic sequence ranging from a plateau at 900 m altitude to a valley at 700 m. In the four different plant formations (Araucaria group on the plateau, ligno-herbaceous maquis, Tristaniopsis maquis and Nothofagus forest in the valley), all plants were consistently colonised by AM fungi, even the sedges Costularia arundinacea, C. nervosa and Lepidosperma perteres and the nickel-hyperaccumulating plant Phyllanthus favieri. Dual (AM and ectomycorrhiza EM) colonisation was observed in the two plant formations dominated by the ectomycorrhizal plants Nothofagus balansae for the forest (site 4) and Tristaniopsis guillainii and T. calobuxus for the Tristaniopsis maquis (site 3). In the soils, there are strong positive correlations between microbial activity, black AM spore abundance and concentrations of available metals indicating the role of the biotic component in the release of metals. These results suggest that these symbioses are important in the adaptation of the endemic plants to these soils, and may be relevant to ecological restoration of the ancient nickel mines.