Diazotrophic bacteria in root-free soil and in the root zone of pine ( Pinus sylvestris L.) and oak ( Quercus robur L.)

Abstract

Studies on the occurrence, identity and potential nitrogenase activity of diazotrophic bacteria in soil and the root zone of Scots pine ( Pinus sylvestris L.) and common oak ( Quercus robur L.) were carried out. Diazotrophic bacteria were more numerous in soil and the root zone of oak than in those of pine. Most of the bacteria isolated from the roots of both trees belonged to the genera Pseudomonas and Bacillus. The majority of these bacteria had nitrogenase activity (tested by the acetylene reduction assay method) within the range from 4 to 20 nmoles C 2H 4 per culture per hour. No clear relationships between the taxonomic identity and/or source of isolation of the bacteria studied and their nitrogenase activity were found. Biotin, p-aminobenzoic acid (PABA) and yeast extract, applied both separately and in combination, significantly (at least several-fold) stimulated the activity of N 2 fixation in three selected (nitrogenase highly active) bacterial strains, as compared to a control without growth factors.