Dynamics of methanogenesis and methanotrophy in tropical paddy soils as influenced by elevated CO2 and temperature interaction

Abstract Response of methanogenesis and methanotrophy to elevated carbon dioxide (CO 2 ) could be affected by changes in soil moisture content and temperature. In soil microcosms contained in glass bottles and incubated under laboratory conditions, we assessed the impact of elevated CO 2 and temperature interactions on methanogenesis and methanotrophy in alluvial and laterite paddy soils of tropical origin. Soil samples were incubated at ambient (370 μmol mol −1 ) and elevated (600 μmol mol −1 ) CO 2 concentrations at 25, 35 and 45 °C under non-flooded and flooded conditions for 60 d. Under flooded condition, elevated CO 2 significantly increased methane (CH 4 ) production while under non-flooded condition, only marginal increase in CH 4 production was observed in both the soils studied and the increase was significantly enhanced by further rise in temperature. Increased methanogenesis as a result of elevated CO 2 and temperature interaction was mostly attributed to decreased soil redox potential, increased readily mineralizable carbon, and also noticeable stimulation of methanogenic bacterial population. In contrast to CH 4 production, CH 4 oxidation was consistently low under elevated CO 2 concentration and the decrease was significant with rise in temperature. The low affinity and high affinity CH 4 oxidation were faster under non-flooded condition as compared to flooded condition. Admittedly, decreased low and high affinity CH 4 oxidation as a result of elevated CO 2 and temperature interaction was related to unfavorable lower redox status of soil and the inhibition of CH 4 -oxidizing bacterial population.