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Thermodynamic controls on soil trace gas (CH4, CO2, N2O) fluxes from the Maui rainfall gradient.
Vile, Melanie*,1, Matson, Pamela2, Hedin, Lars1, 1 Department of Ecology and Evolutionary Biology, Princeton, NJ, USA2 Department of Geological and Environmental Sciences, Stanford, CA, USA
ABSTRACT- Predictions of ecosystem-scale emissions of trace gases are mired in large temporal and spatial variability. Much of this variability is likely caused by thermodynamic factors operating at the microsite scale. We wanted to determine if a thermodynamic perspective can enhance our mechanistic understanding and predictive capability of trace gas emissions at sites on the Maui rainfall gradient, where all state factors are constant but rainfall varies between 2200 mm, and 4050 mm. In laboratory incubations, we manipulated water and carbon (C) in soil cores from both sites to test the importance of these two thermodynamic factors in constraining trace gas fluxes. Both water, and water plus C additions increased CH4 production significantly at the drier site, and caused a shift from net CH4 consumption to net CH4 production. At the wet site, both addition treatments caused significant increases in CH4 production, with net production of CH4 measured in all cores, including controls. Nitrous oxide production showed the same responses as CH4 to water and water plus C additions with a much larger increase in production measured at the drier site. Soils from the drier site always showed net CH4 production while water and water plus C treatments provoked a shift from net NO2 consumption to production at the wet site. Production of CO2 decreased significantly in both water and water plus C-amended cores relative to controls at both sites. Production of NO2, CH4 and CO2in water and water plus C treatments were statistically indistinguishable at both sites. These results suggest that water has a greater thermodynamic control than labile C over trace gas emissions from soils along the Maui rainfall gradient.
Key words: nitrous-oxide, rainforest, methane, carbon-dioxide