The Diversity and Co-occurrence Patterns of N₂-Fixing Communities in a CO₂-Enriched Grassland Ecosystem.
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.
Department of Marine Sciences, Ocean College, Zhejiang University, Hangzhou, Zhejiang, 310058, China.|Institute for Environmental Genomics and Department of Microbiology and Plant Biology, The University of Oklahoma, Norman, OK, 73019, USA.
Qichao
Q
Tu
Institute for Environmental Genomics and Department of Microbiology and Plant Biology, The University of Oklahoma, Norman, OK, 73019, USA.|School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, 410083, China.
Xishu
X
Zhou
School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, 410083, China.
Zhili
Z
He
School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, 410083, China.
Kai
K
Xue
School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, 410083, China.
Liyou
L
Wu
Department of Forest Resources, University of Minnesota, St. Paul, MN, 55455, USA.|Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, 2753, NSW, Australia.
Peter
P
Reich
Department of Forest Resources, University of Minnesota, St. Paul, MN, 55455, USA.
Sarah
S
Hobbie
Institute for Environmental Genomics and Department of Microbiology and Plant Biology, The University of Oklahoma, Norman, OK, 73019, USA. jzhou@ou.edu.|Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. jzhou@ou.edu.|State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China. jzhou@ou.edu.
Jizhong
J
Zhou
D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D044822:Biodiversity; D002245:Carbon Dioxide / Q000378:metabolism*; D017753:Ecosystem; D065948:Grassland; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D010802:Phylogeny; D012988:Soil Microbiology
D002245:Carbon Dioxide; D009584:Nitrogen
Co-occurrence patterns; Community structure; Elevated CO2; Soil diazotrophs; nifH