My work consists in understanding the ecological role of a nitrogen-fixing tree on the soil supply of macroelements (N, S and P) for the associated crop (temperate climate agroforestry system). A first approach aims at studying the behavior of physico-chemical parameters of the soil of an experimental agroforestry plot in relation with the taxonomic and functional diversity of the microbial communities present. A second approach under controlled conditions will evaluate the modulation of root traits related to potential macroelement interception efficiency or competition between the two plant species.