Nodule Function in Symbiotic Bambara Groundnut (Vigna subterraneaL.) and Kersting's Bean (Macrotyloma geocarpumL.) is Tolerant of Nitrate in the Root Medium

Nitrogen-fixing activity in two nodulated African legumes, Bambara groundnut ( Vigna subterranea L.) and Kersting's bean ( Macrotyloma geocarpum L.), was assessed in the presence of nitrate (NO 3− ) ions in the rooting medium. Nitrogenase activity was unimpaired by the supply of 5 mol m −3 NO 3 to both species. Also, large concentrations of ureides dominated the transpiration stream of NO 3 -fed plants. Compared to other symbiotic legumes cultured with similar NO 3 concentrations, nodule functioning in the tested landraces of Bambara groundnut and Kersting's bean is tolerant of NO 3 ions in the rhizosphere. The potential benefits of such naturally occurring NO 3 -tolerant symbioses are substantial, as they would permit inorganic N fertilizer application in intercropping systems without inhibiting N 2 fixation in the associated legumes.