Biological Nitrogen Fixation and Root-Nodule Bacteria (Rhizobium Sp. and Bradyrhizobium Sp.) In Two Rehabilitating Sand Dune Areas Planted With Acacia Spp

Abstract

This paper reports a study of biological nitrogen fixation in two sand dune regions of New South Wales where planted Acacia spp. had been used in revegetation programmes. At one location (Bridge Hill Ridge), natural regrowth had produced a complex plant community, and native legumes in addition to the planted acacias were present. The other area (Wanda Beach) was a grossly disturbed site which contained only the planted species. Symbiotic fixation in association with Australian legumes occurred at both locations at rates within the range reported by other authors. Distinct seasonal changes were apparent, with higher activities in the cooler months. The legume association seemed the only source of biologically fixed nitrogen at Bridge Hill Ridge, but at Wanda Beach cyanobacteria in an algal mat also made a contribution. Fast and slow-growing bacterial strains were obtained from root nodules of native legumes at both sites and were classed as Rhizobium sp. and Bradyrhizobium sp., respectively. This division was supported by the pattern of serological affinities of the isolates and by differences in their protein profiles demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two atypical types of root-nodule bacteria were found at Bridge Hill Ridge: non-nodulating, fast-growing isolates and an abnormally slow-growing Bradyrhizobium sp.