Soil nitrogen balance resulting from N fixation and rhizodeposition by the symbiotic association Anthyllis vulneraria/Mesorhizobium metallidurans grown in highly polluted Zn, Pb and Cd mine tailings
2014
Mahieu, Stéphanie | Escarré, José | Brunel, Brigitte | Méjamolle, Angélique | Soussou, Souhir | Galiana, Antoine | Cleyet-Marel, Jean-Claude
BACKGROUND AND AIMS: The association of the legume Anthyllis vulneraria and the grass Festuca arvernensis, was found to be very efficient for the phytostabilisation of highly multi-metal contaminated mine tailings. Our objective was to quantify the contribution of Anthyllis inoculated with its symbiotic bacteria Mesorhizobium metallidurans to the soil N pool and to test whether a starter nitrogen fertilization may improve symbiotic nitrogen fixation and the growth of Festuca. METHODS: Plants of Festuca and of Anthyllis inoculated with M. metallidurans were grown separately during eight months in pots filled with mine contaminated soil. Estimation of the N fluxes was realized using¹⁵ N isotopic methods. RESULTS: Starter N fertilization (28 kg N ha⁻¹) improved symbiotic N₂fixation and the growth of both species. Belowground N balance (N rhizodeposition – soil N uptake) of the non-fertilized Anthyllis at maturity was negative (−30.6 kg N ha⁻¹). However, the amount of N derived from fixation, including above- and belowground parts, was 78.6 kg N ha⁻¹, demonstrating the ability of this symbiotic association to improve soil N content after senescence. CONCLUSIONS: i) soil N enrichment by the N₂-fixing symbiotic association occurs after plant senescence, when decaying leaves and shoots are incorporated into the soil; ii) application of a starter fertilization is an efficient solution to improve phytostabilisation of highly contaminated sites.
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