Associative nitrogen-fixing bacteria in the rhizosphere of Avena sativa in an alpine region I Isolation and identification

This study isolates and identifies associative nitrogen-fixing bacteria (ANB) from the rhizosphere of Avena sativa in an alpine region by acetylene reduction assay (ARA) combined with gas chromatography (GC). Eight ANB strains were found. Strain distribution was related to root proximity,with the majority found on the root surface (RP), followed by those within soil by roots (RS), soil away from roots (NRS), and the least found within roots (HP). Nitrogenase activity showed large variation between strains (C2H4 112.5-(1 147.9) nmol/mL·h). Only 2 strains showed nitrogenase activity higher than C2H4 500 nmol/mL·h. All the strains obtained were gram-negative, and belonged to Azotobacter (3 strains), Pseudomonas (3 strains) and Azospirillus (2 strains) genera. The ANB species found in the rhizosphere of A.sativa in this alpine region are relatively few compared with other plants and habitats.