Carbon isotope fractionation by methane-oxidizing bacteria intropical rain forest soils
Humid tropical forests have the potential to be significantsources or sinks of atmospheric methane (CH4), a radiatively importanttrace gas. Methane oxidation can consume a large fraction of the CH4produced in tropical soils, although controls on this process are poorlyunderstood. Using soil incubation experiments, we investigated theeffects of CH4 and oxygen (O2) concentrations on C isotope fractionationand CH4 oxidation in tropical rain forest soils. We also explored theeffects of these environmental variables on the isotope fractionationfactor for CH4 oxidation (alpha), which is widely used to evaluate therelative contributions of CH4 production and oxidation to the atmosphericCH4 pool. Methane oxidation was sensitive to CH4 at lower CH4concentrations (<850 ppmv) and insensitive to O2 concentrationsbetween 3 and 21 percent. Maximum rates of CH4 oxidation were between 8.2+- 1.2 and 11.3 +- 1.5 nmol CH4 hour-1 g dry soil-1. Measured values foralpha were sensitive to both CH4 oxidation rate and CH4 concentration.Alpha was inversely proportional to CH4 oxidation rate (r2 = 0.86, P<0.001) and positively correlated with CH4 concentration (r2 = 0.52, P<0.01). A multiple regression model that included CH4 oxidation rate,CH4 concentration, and the interaction of the two terms explained a highproportion of the variability in alpha (r2 = 0.94, P<0.0001). Thesedata suggest that it is possible to accurately determine alpha, allowingfor more precise estimates of CH4 oxidation by isotope massbalance.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Office of Basic EnergySciences. Chemical Sciences Geosciences and Biosciences Division; National Aeronautics and Space Administration Fellowship NGT5-50331,National Science Foundation Grants DEB-0206547 and BSR-8811902; California Agricultural Experiment Station 7069-MS
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 901042
- Report Number(s):
- LBNL-60692; JGREA2; R&D Project: 468202; BnR: KC0303020; TRN: US200711%%769
- Journal Information:
- Journal of Geophysical Research, Vol. 111; Related Information: Journal Publication Date: June 2006; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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