Oxygen effects on methane production and oxidation in humid tropical forest soils
We investigated the effects of oxygen (O2) concentration on methane (CH4) production and oxidation in two humid tropical forests that differ in long‐term, time‐averaged soil O2 concentrations. We identified sources and sinks of CH4 through the analysis of soil gas concentrations, surface emissions,...
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Published in | Global change biology Vol. 11; no. 8; pp. 1283 - 1297 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
Blackwell Science Ltd
01.08.2005
Blackwell Publishing Ltd |
Subjects | |
Online Access | Get full text |
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Summary: | We investigated the effects of oxygen (O2) concentration on methane (CH4) production and oxidation in two humid tropical forests that differ in long‐term, time‐averaged soil O2 concentrations. We identified sources and sinks of CH4 through the analysis of soil gas concentrations, surface emissions, and carbon isotope measurements. Isotope mass balance models were used to calculate the fraction of CH4 oxidized in situ. Complementary laboratory experiments were conducted to determine the effects of O2 concentration on gross and net rates of methanogenesis. Field and laboratory experiments indicated that high levels of CH4 production occurred in soils that contained between 9±1.1% and 19±0.2% O2. For example, we observed CH4 concentrations in excess of 3% in soils with 9±1.1% O2. CH4 emissions from the lower O2 sites were high (22–101 nmol CH4 m−2 s−1), and were equal in magnitude to CH4 emissions from natural wetlands. During peak periods of CH4 efflux, carbon dioxide (CO2) emissions became enriched in 13C because of high methanogenic activity. Gross CH4 production was probably greater than flux measurements indicated, as isotope mass balance calculations suggested that 48–78% of the CH4 produced was oxidized prior to atmospheric egress. O2 availability influenced CH4 oxidation more strongly than methanogenesis. Gross CH4 production was relatively insensitive to O2 concentrations in laboratory experiments. In contrast, methanotrophic bacteria oxidized a greater fraction of total CH4 production with increasing O2 concentration, shifting the δ13C composition of CH4 to values that were more positive. Isotopic measurements suggested that CO2 was an important source of carbon for methanogenesis in humid forests. The δ13C value of methanogenesis was between −84‰ and −98‰, which is well within the range of CH4 produced from CO2 reduction, and considerably more depleted in 13C than CH4 formed from acetate. |
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Bibliography: | ArticleID:GCB983 istex:F93421FE3987FE4859B26F821A0079C628647734 ark:/67375/WNG-QNTQPNWG-5 ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 1354-1013 1365-2486 |
DOI: | 10.1111/j.1365-2486.2005.00983.x |