Forest soil carbon oxidation state and oxidative ratio responses to elevated CO2
- Baylor Univ., Waco, TX (United States). Dept. of Geology
- Rice Univ., Houston, TX (United States). Dept. of Earth Science
- CSIRO Land and Water, Glen Osmond SA (Australia)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Climate Change Science Inst. and Environmental Sciences Division
The oxidative ratio (OR) of the biosphere is the stoichiometric ratio (O2/CO2) of gas exchange by photosynthesis and respiration a key parameter in budgeting calculations of the land and ocean carbon sinks. Carbon cycle-climate feedbacks could alter the OR of the biosphere by affecting the quantity and quality of organic matter in plant biomass and soil carbon pools. Here, this study considers the effect of elevated atmospheric carbon dioxide concentrations ([CO2]) on the OR of a hardwood forest after nine growing seasons of Free-Air CO2 Enrichment. We measured changes in the carbon oxidation state (Cox) of biomass and soil carbon pools as a proxy for the ecosystem OR. The OR of net primary production, 1.039, was not affected by elevated [CO2]. However, the Cox of the soil carbon pool was 40% higher at elevated [CO2], and the estimated OR values for soil respiration increased from 1.006 at ambient [CO2] to 1.054 at elevated [CO2]. A biochemical inventory of the soil organic matter ascribed the increases in Cox and OR to faster turnover of reduced substrates, lignin and lipids, at elevated [CO2]. This implicates the heterotrophic soil community response to elevated [CO2] as a driver of disequilibrium in the ecosystem OR. The oxidation of soil carbon pool constitutes an unexpected terrestrial O2 sink. Carbon budgets constructed under the assumption of OR equilibrium would equate such a terrestrial O2 sink to CO2 uptake by the ocean. We find that the potential for climate-driven disequilibriua in the cycling of O2 and CO2 warrants further investigation.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge National Environmental Research Park
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- AC05-00OR22725; DEB 0445282; DEB 0614524; EAR 1132124
- OSTI ID:
- 1328279
- Journal Information:
- Journal of Geophysical Research. Biogeosciences, Vol. 120, Issue 9; ISSN 2169-8953
- Publisher:
- American Geophysical UnionCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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