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Journal of Agronomy and Crop Science 193 (2007) 153-156
Effect of Microbial Activity and Nitrogen Mineralization on Free-living Nitrogen Fixation in Permanent Grassland Soils
Ashok Patra 1, Xavier Le Roux 1, Luc Abbadie 2, Annie Clays-Josserand 1, Franck Poly 1, P. Loiseau 3, Frédérique Louault 3
(2007)

Free-living nitrogen (N) fixation can be important for sustainable soil fertility, particularly in extensively managed soils with low abundance of leguminous plant species. However, the factors affecting free N2-fixation in situ are still poorly documented. We investigated the role of microbial active biomass activity, particularly substrateinduced respiration (SIR) and net N mineralization, on the free-living N2 fixation in soils under a semi-natural grassland ecosystem in France. Analysis of replicated bulk soil and rhizospheric soil samples obtained from sites experiencing contrasting grazing regimes revealed highly signifi- cant negative relationships (P < 0.01) between free-living N2-fixation and SIR or N-mineralization with a significant rhizosphere effect. The study has demonstrated that the activity of free-living N2-fixers is more important in soils having low active microbial biomass and low N-mineralization rates in these permanent grasslands.
1 :  Ecologie microbienne (EM)
CNRS : UMR5557 – INRA : UR1193 – Université Claude Bernard - Lyon I – Ecole Nationale Vétérinaire de Lyon
2 :  Ecologie et évolution
CNRS : UMR7625 – Université Paris VI - Pierre et Marie Curie – Ecole Normale Supérieure de Paris - ENS Paris
3 :  Unité d'Agronomie Site de Crouel
INRA
Sciences de l'environnement/Biodiversité et Ecologie

Sciences du Vivant/Biodiversité

Sciences du Vivant/Ecologie, Environnement
Key words: carbon mineralization — free-living N2-fixation — grasslands — microbial activity — N-cycling — N-mineralization