Effects of different land use patterns on nifH genetic diversity of soil nitrogen-fixing microbial communities in Leymus Chinensis steppe

Biological nitrogen fixation through prokaryotic microbe is an important source of nitrogen been input into many natural ecosystems. In this study the active diazotrophic community was investigated in the three treatments of mowed, grazed and enclosed Leymus chinensis steppes in Hulunbeier grassland of Inner Mongolia by using approaches of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR–DGGE) and sequence analysis. The community structure and diversity of the bacterial groups from the different samples was further analyzed by using different techniques, such as statistical analysis and diversity index evaluation of the band patterns etc. The results showed that grazing activity significantly reduced the number of species and quantities of nitrogen-fixing microorganisms, as well as the nifH gene diversity. However, enclosed plots had the lowest diversity of nifH gene. While the highest one found in mowing plots. A total of 30 sequences representing 25 different sequence types were recovered from the DGGE gels after phylogenetic constructions. The results also revealed that most sequences were coming from Alphaproteobacteria of Proteobacteria, and characterized by sequences of members of Rhodobacter, Bradyrhizobium, Mesorhizobium, Rhodopseudomonas, Xanthomonas, Azospirillum, Gluconacetobacter, Methylobacterium and Methylocystis. Symbiotic nitrogen-fixers existed in grazing, mowing and enclosed plots accounted for 21.4%, 47.3% and 31.3% respectively in their dominant nitrogen-fixing bacteria. The result of principal components analysis showed that the influence of different land use patterns on nitrogen-fixing microbial communities composition can be ordered as grazing plots > enclosed plots > mowing plots. Nitrogen-fixing microbial communities in L. chinensis steppe were significantly (P