NODULE FUNCTION IN SYMBIOTIC BAMBARA GROUNDNUT (VIGNA-SUBTERRANEA L.)AND KERSTINGS BEAN (MACROTYLOMA-GEOCARPUM L.) IS TOLERANT OF NITRATE IN THE ROOT MEDIUM

Nitrogen-fixing activity in two nodulated African legumes, Bambara gro undnut (Vigna subterranea L.) and Kersting's bean (Macrotyloma geocarp um L.), was assessed in the presence of nitrate (NO3-) ions in the roo ting medium. Nitrogenase activity was unimpaired by the supply of 5 mo l m(-3) NO3 to both species. Also, large concentrations of ureides dom inated the transpiration stream of NO3-fed plants. Compared to other s ymbiotic legumes cultured with similar NO3 concentrations, nodule func tioning in the tested landraces of Bambara groundnut and Kersting's be an is tolerant of NO3 ions in the rhizosphere. The potential benefits of such naturally occurring NO3-tolerant symbioses are substantial, as they would permit inorganic N fertilizer application in intercropping systems without inhibiting N-2 fixation in the associated legumes. (C ) 1998 Annals of Botany Company.