title: Dinitrogen fixation of microbe-plant associations as affected by nitrate and ammonium supply.
abstract: Abstract   The dinitrogen fixation activity of Azospirillum sp., and Pantoea agglomerans strains was determined by (15)N(2) incorporation after incubation with (15)N(2) labeled air or/and by acetylene reduction. These bacterial strains were able to fix N(2) both in pure culture and in association with wheat plants in hydroponics. Nitrogenase activity of Azospirillum sp., in pure culture was more rapidly inhibited by the addition of NH(4) (+) than NO(3) (-). The N(2) fixation of P. agglomerans decreased only by NH(4) (+) -addition, but was stimulated by NO(3) (-). Nitrogen fixation in association with wheat plants remained unaffected by both N compounds. However, nitrogen derived from the atmosphere (N(dfa)) contributed only very little to the overall nitrogen nutrition of the plants.
authors.affiliation: a    Institut für Bodenkunde und Pflanzenernährung der Martin-Luther-Universität   ,  Halle-Wittenberg ,    Deutschland.
authors.forename: W
authors.initials: W
authors.lastname: Merbach
authors.forename: S
authors.initials: S
authors.lastname: Ruppel
authors.forename: J
authors.initials: J
authors.lastname: Schulze