Isolation, characterization, and inoculation of N2-fixing bacteria from dicotyledonous plants

Abstract

N2-flxing (acetylene-reducing) bacteria were isolated from roots of five species of wild plants in southern New Mexico. Ground cherry (Physalis wrightii) had the highest frequency of roots with N2-fixing bacteria. Acetylene reduction rates of subcultures were comparable with rates exhibited by Azospirillum (300–500 nmol ethylene∙h−1). Three isolates from ground cherry were characterized to the generic level and one to the level of genus and species. Three of these isolates were identified as Enterobacter spp, while the fourth isolate was identified as Azospirillum brasilense. Inoculation of ground cherry with N2-fixing isolates had minimal effects on plant growth, plant nitrogen content, or plant acetylene reduction activity 7 weeks after inoculation. Comparisons between uninoculated and inoculated plants were generally not statistically significant. Significant acetylene reduction activity and high numbers of N2-fixing bacteria occurred only on the roots of plants grown with little or no added nitrogen.