Influence of nitrogen on the number of N2-fixing and total bacteria in the rhizosphere

摘要: Abstract Various grass and herbaceous plant species (e.g. Arrhenatherum elatius L., Phleum pratense Planlago media Taraxacum officinale WEB.) were cultivated in a freshly collected soil from an unfertilized grassland area with its natural population of N2-fixing bacteria. Diazotrophs total bacteria at the root surface (at outer plus “inner” as recovered homogenate) rhizosphere (0–3 mm surface) counted by most probable number (MPN) method. Addition mineral N (NH4NO3) to decreased nitrogenase activity (assayed acetylene reduction) also proportion diazotrophs among heterotrophs. The result was similar when supplied via leaves, probably owing increased release N-containing compounds lower C:N ratios root. decrease suggests competitive suppression non-diazotrophs presence combined N. Correspondingly, increase MPN found during development is interpreted soil, particularly rhizosphere, uptake addition, N-concentration concomitant change ratio released varied greatly but for living on or within roots than soil. Most members genera Klebsiella Enterobacter. Species Azospirillum represented only small counts.