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.

Global dynamics of the buffered chemostat for a general class of response functions

“…However, in many applications, the assumption of perfectly stirred chemostats is, in general, too restrictive. In the eighties, the gradostat, as an experimental device composed of a set of chemostats of identical volume interconnected in series, was introduced to represent spatial gradient [31], in a marine environment [21] or to model rhizosphere [13]. It motivated several mathematical studies [49,23,10,43,54,45,20,47,14].…”

The buffered chemostat with non-monotonic response functions

“…In the eighties, the gradostat, as an experimental device composed of a set of chemostats of identical volume interconnected in series, has been proposed to represent spatial gradient [25]. For instance, it has been used to reproduce marine environment [18] or to model rhizosphere [11], and has motivated several mathematical studies [43,20,9,37,47,39,17,41,12]. Similarly, an interest for series of bioreactors appeared in biochemical industry, with tanks of possibly different volumes to be optimized [26,19,4,15,8].…”