Compensation occurs when consumption is balanced by simultaneous production. Trace gas consumption generally increases with ambient trace gas concentration. However, trace gas production is normally independent of the product concentration. Therefore, there exists a concentration level for a specific gas at which its production equals consumption, the so called compensation point. Methane production has two pathways: an insignificant H2-supported and a vigorous acetate-dependent methanogenesis. Methane consumption mechanism involves both aerobic and anaerobic oxidation.

To study methane compensation point under different Eh conditions, six soils used for rice production were incubated using an automatic microcosm system that allows controlling soil redox potential (Eh) and monitoring gas concentration and soil pH. In such a closed system, two approaches for measuring CH4 compensation point were implemented. One was to monitor CH4 concentration increasing in the headspace of microcosms until it reached a steady state, and the other was to monitor CH4 concentration decreasing to a steady state.

Under low Eh conditions, a high CH4 compensation point was found due to strong CH4 production and weak CH4 oxidation capacity. The methane compensation point was low under high Eh conditions due to strong methanotrophy activity and weak methanogenesis activity. This analysis was applied to each soil over the entire Eh range studied, and the results showed that the CH4 compensation point decreased exponentially with increasing soil Eh. For all studied soils, the results clearly showed the reverse relationship between the CH4 compensation concentration and soil Eh. The critical Eh where CH4 compensation point equals ambient atmospheric CH4 concentration is important, above which soils start to consume atmospheric CH4. Such critical Eh values varied among different soils studied. Regression analysis indicated that the critical Eh value was +414 mV for all soils combined, above which the soils functioned as a sink of atmospheric CH4.