Diversity of nifH gene in rhizosphere and non-rhizosphere soil of tobacco in Panzhihua, China

To gain a better understanding of the effects of tobacco root secretions on the nifH gene community of rhizosphere soil, the diversity of the nifH gene in the rhizosphere and non-rhizosphere soil of tobacco was investigated using denaturing gradient gel electrophoresis (DGGE) and sequencing. Shannon diversity (H), richness (S) and evenness (EH) indices were used to analyze the DGGE results. The results showed that the nifH gene diversity for rhizosphere soil was lower than that of the non-rhizosphere at three sampling sites. The increase in H of non-rhizosphere soil was due mainly to the increase in pH and the decrease in available N. Richness was correlated closely with H. There was a great difference of evenness between the rhizosphere and the non-rhizosphere samples. A range of sequence divergence was observed in the eight sequenced nifH clones. The sequences were divided into three clusters in the phylogenetic tree. The majority of the clones were similar to the nifH genes of Betaproteobacteria, Zoogloea oryzae, Dechloromonas sp. and Azovibrio restrictus. There was a difference regarding dominant species between the rhizosphere and the non-rhizosphere samples.