The Diversity and Co-occurrence Patterns of N2-Fixing Communities in a CO2-Enriched Grassland Ecosystem

Qichao Tu, Xishu Zhou, Zhili He, Kai Xue, Liyou Wu, Peter Reich, Sarah Hobbie, Jizhong Zhou

Research output: Contribution to journalArticlepeer-review

49 Scopus citations


Diazotrophs are the major organismal group responsible for atmospheric nitrogen (N2) fixation in natural ecosystems. The extensive diversity and structure of N2-fixing communities in grassland ecosystems and their responses to increasing atmospheric CO2 remain to be further explored. Through pyrosequencing of nifH gene amplicons and extraction of nifH genes from shotgun metagenomes, coupled with co-occurrence ecological network analysis approaches, we comprehensively analyzed the diazotrophic community in a grassland ecosystem exposed to elevated CO2 (eCO2) for 12 years. Long-term eCO2 increased the abundance of nifH genes but did not change the overall nifH diversity and diazotrophic community structure. Taxonomic and phylogenetic analysis of amplified nifH sequences suggested a high diversity of nifH genes in the soil ecosystem, the majority belonging to nifH clusters I and II. Co-occurrence ecological network analysis identified different co-occurrence patterns for different groups of diazotrophs, such as Azospirillum/Actinobacteria, Mesorhizobium/Conexibacter, and Bradyrhizobium/Acidobacteria. This indicated a potential attraction of non-N2-fixers by diazotrophs in the soil ecosystem. Interestingly, more complex co-occurrence patterns were found for free-living diazotrophs than commonly known symbiotic diazotrophs, which is consistent with the physical isolation nature of symbiotic diazotrophs from the environment by root nodules. The study provides novel insights into our understanding of the microbial ecology of soil diazotrophs in natural ecosystems.

Original languageEnglish (US)
Pages (from-to)604-615
Number of pages12
JournalMicrobial Ecology
Issue number3
StatePublished - Apr 1 2016

Bibliographical note

Publisher Copyright:
© 2015, Springer Science+Business Media New York.


  • Co-occurrence patterns
  • Community structure
  • Elevated CO
  • nifH
  • Soil diazotrophs

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.


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