Structure of Community of (Dizotrophs) Nitrogen-Fixing Bacteria.

Microorganisms involved in nitrogen fixation play important roles in the biosphere. Organic fertilizers are employed to improve red soil quality which are often N limited. To understand the effects of organic manure on the composition and structure of diazotrophs communities in red soils, the molecular diversity of diazotrophs was examined using a PCR based cloning approach with nifH as functional gene marker. The typical red soil was sampled from the Ecology Experiment Station of Red Soil in Jiangxi Province, China (281o20'N,and 116o53'E). The experiment included four treatments: the control (without fertilization), low organic manure (LM), high organic manure(HM) and high organic manure amended with lime(ML). The results of RFLP patterns demonstrated that the main pattern of clones accounted for overly (above) 82% in clone library of HM, about 50-60% in other libraries. nifH clones of the main pattern which were sequenced and identical with nitrogenase reductase (about 96% similarity) . Some of the clone sequences of LM library were related to nifH genes belonging to four phylogenetic subdivisions (Cyanobactera and ¦Á, ¦Â, ¦Ã subclasses of the Proteobacteria) in our phylogenetic tree, however the nifH genes of HM and ML library only belonging to the subdivision of Cyanobacteria. High P/N was the main reason which affected the diversity (communities) of diazotrophs in red soil. The nifH sequences of the dominant patterns in all libraries were most similar to sequences of the Cyanobacteria.