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Title: Molybdenum-Based Diazotrophy in a Sphagnum Peatland in Northern Minnesota

We present that Microbial N 2 fixation (diazotrophy) represents an important nitrogen source to oligotrophic peatland ecosystems, which are important sinks for atmospheric CO 2 and are susceptible to the changing climate. The objectives of this study were (i) to determine the active microbial group and type of nitrogenase mediating diazotrophy in an ombrotrophic Sphagnum-dominated peat bog (the S1 peat bog, Marcell Experimental Forest, Minnesota, USA); and (ii) to determine the effect of environmental parameters (light, O 2, CO 2, and CH 4) on potential rates of diazotrophy measured by acetylene (C 2H 2) reduction and 15N 2incorporation. A molecular analysis of metabolically active microbial communities suggested that diazotrophy in surface peat was primarily mediated by Alphaproteobacteria (15N 2 was suppressed 90% by O 2 and 55% by C 2H 2 and was unaffected by CH 4 and CO 2 amendments. These results suggest that peatland diazotrophy is mediated by a combination of C 2H 2-sensitive and C 2H 2-insensitive microbes that are more active at low concentrations of O 2 and show similar activity at high and low concentrations of CH 4. Importance: Previous studies indicate that diazotrophy provides an important nitrogen source and is linked to methanotrophy inmore » Sphagnum-dominated peatlands. However, the environmental controls and enzymatic pathways of peatland diazotrophy, as well as the metabolically active microbial populations that catalyze this process, remain in question. In conclusion, our findings indicate that oxygen levels and photosynthetic activity override low nutrient availability in limiting diazotrophy and that members of the Alphaproteobacteria (Rhizobiales) catalyze this process at the bog surface using the molybdenum-based form of the nitrogenase enzyme.« less
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  1. Georgia Inst. of Technology, Atlanta, GA (United States). School of Earth and Atmospheric Sciences
  2. Georgia Inst. of Technology, Atlanta, GA (United States). School of Biological Sciences
  3. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Sciences Directorate
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Divison
  6. Georgia Inst. of Technology, Atlanta, GA (United States). School of Earth and Atmospheric Sciences and School of Biological Sciences
Publication Date:
Grant/Contract Number:
AC05-00OR22725; SC0007144; SC0012088; AC52-07NA27344
Accepted Manuscript
Journal Name:
Applied and Environmental Microbiology
Additional Journal Information:
Journal Volume: 83; Journal Issue: 17; Journal ID: ISSN 0099-2240
American Society for Microbiology
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Alphaproteobacteria; Sphagnum; acetylene; diazotrophy; methanotrophs; molybdenum; nitrogen cycle enzymes; nitrogen fixation; peatland; vanadium
OSTI Identifier: