Ecophysiology of associative nitrogen fixation in a rhizosphere model in pure and mixed culture

Abstract A gradostat (multistage chemostat) was used as a model of the rhizosphere. Investigations of the influence of NH₄Cl and O₂ gradients on a diazotrophic rhizosphere bacterium in pure culture and in mixed culture with non-diazotrophic strains were carried out. The diazotrophic isolate was able to grow on N₂ and NH₄Cl simultaneously. The diazotrophic isolate could successfully compete with the non-diazotrophic isolates in the presence and absence of NH₄Cl in most experiments. Only minor amounts of nitrogen were transferred to the non-fixing organisms. A concept of transfer of nitrogen to non-fixing organisms is proposed.