Oxygen effects on methane production and oxidation in humidtropical forest soils
We investigated the effects of oxygen (O2) concentration onmethane (CH4) production and oxidation in two humid tropical forests thatdiffer in long-term, time-averaged soil O2 concentrations. We identifiedsources and sinks of CH4 through the analysis of soil gas concentrations,surface emissions, and carbon isotope measurements. Isotope mass balancemodels were used to calculate the fraction of CH4 oxidized in situ.Complementary laboratory experiments were conducted to determine theeffects of O2 concentration on gross and net rates of methanogenesis.Field and laboratory experiments indicated that high levels of CH4production occurred in soils that contained between 9+-1.1 percent and19+-0.2 percent O2. For example, we observed CH4 concentrations in excessof 3 percent in soils with 9+-1.1 percent O2. CH4 emissions from thelower O2 sites were high (22-101 nmol CH4m2s1), and were equal inmagnitude to CH4 emissions from natural wetlands. During peak periods ofCH4 efflux, carbon dioxide (CO2) emissions became enriched in 13C becauseof high methanogenic activity. Gross CH4 production was probably greaterthan flux measurements indicated, as isotope mass balance calculationssuggested that 48-78 percent of the CH4 produced was oxidized prior toatmospheric egress. O2 availability influenced CH4 oxidation morestrongly than methanogenesis. Gross CH4 production was relativelyinsensitive to O2 concentrations in laboratory experiments. In contrast,methanotrophic bacteria oxidized a greater fraction of total CH4production with increasing O2 concentration, shifting the delta13Ccomposition of CH4 to values that were more positive. Isotopicmeasurements suggested that CO2 was an important source of carbon formethanogenesis in humid forests. The delta13C value of methanogenesis wasbetween -84 percent and -98 percent, which is well within the range ofCH4 produced from CO2 reduction, and considerably more depleted in 13Cthan CH4 formed from acetate.
- 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 andBSR-8811902
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 901043
- Report Number(s):
- LBNL-60693; GCBIFE; R&D Project: 468202; BnR: KC0303020; TRN: US200711%%770
- Journal Information:
- Global Change Biology, Vol. 11; Related Information: Journal Publication Date: May 4 2005; ISSN 1354-1013
- Country of Publication:
- United States
- Language:
- English
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