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Title: Ecosystem fluxes of hydrogen in a mid-latitude forest driven by soil microorganisms and plants

Molecular hydrogen (H 2 ) is an atmospheric trace gas with a large microbe-mediated soil sink, yet cycling of this compound throughout ecosystems is poorly understood. Measurements of the sources and sinks of H 2 in various ecosystems are sparse, resulting in large uncertainties in the global H 2 budget. Constraining the H 2 cycle is critical to understanding its role in atmospheric chemistry and climate. We measured H 2 fluxes at high frequency in a temperate mixed deciduous forest for 15 months using a tower-based flux-gradient approach to determine both the soil-atmosphere and the net ecosystem flux of H 2 . We also found that Harvard Forest is a net H 2 sink (-1.4 ± 1.1 kg H 2  ha -1 ) with soils as the dominant H 2 sink (-2.0 ± 1.0 kg H 2  ha -1 ) and aboveground canopy emissions as the dominant H 2 source (+0.6 ± 0.8 kg H 2  ha -1 ). Aboveground emissions of H 2 were an unexpected and substantial component of the ecosystem H 2 flux, reducing net ecosystem uptake by 30% of that calculated from soil uptake alone. Soil uptake was highly seasonal (July maximum, February minimum), positively correlated with soil temperature and negatively correlated with environmental variables relevantmore » to diffusion into soils (i.e., soil moisture, snow depth, snow density). Soil microbial H 2 uptake was correlated with rhizosphere respiration rates (r = 0.8, P  <  0.001), and H 2 metabolism yielded up to 2% of the energy gleaned by microbes from carbon substrate respiration. Here, we elucidate key processes controlling the biosphere–atmosphere exchange of H 2 and raise new questions regarding the role of aboveground biomass as a source of atmospheric H 2 and mechanisms linking soil H 2 and carbon cycling. Our results should be incorporated into modeling efforts to predict the response of the H 2 soil sink to changes in anthropogenic H 2 emissions and shifting soil conditions with climate and land-use change.« less
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ; ORCiD logo [2] ;  [5] ;  [6] ;  [2] ;  [7]
  1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson AZ USA; Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge MA USA
  2. Department of Earth and Planetary Science, School of Engineering and Applied Sciences, Harvard University, Cambridge MA USA
  3. Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley CA USA
  4. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge MA USA
  5. Department of Biology, Boston University, Boston MA USA
  6. Ecosystems Center, Marine Biological Laboratory, Woods Hole MA USA
  7. Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge MA USA
Publication Date:
Grant/Contract Number:
AC02-05CH11231; SC0004985; SC0006951; DBI-959333; AGS-1005663; DEB-1237491; EF-1065029
Accepted Manuscript
Journal Name:
Global Change Biology
Additional Journal Information:
Journal Volume: 23; Journal Issue: 2; Journal ID: ISSN 1354-1013
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; 59 BASIC BIOLOGICAL SCIENCES; hydrogen; flux; soil; microbe; atmosphere; phenology; snow; carbon cycle
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1400787