The inhibitory effect of difluoromethane on CH4 oxidation in reconstructed peat columns and side-effects on CO2 and N2O emissions at two water levels

Methane emissions from soils are the net result of two processes: methane (CH4) production and CH4 oxidation. In order to understand how both processes respond to environmental changes, it is necessary to distinguish between CH4 production and oxidation. In bacterial cultures and small soil samples, difluoromethane (CH2F2) was found to inhibit CH4 oxidation reversibly, without affecting CH4 production. Hence, CH2F2 allows the study of CH4 production directly and of CH4 oxidation indirectly. To our knowledge, however, the inhibitory effect of CH2F2 within soil columns has not yet been evaluated. We therefore tested which CH2F2 concentration is needed for complete inhibition of CH4 oxidation in reconstructed 28 cm high peat soil columns under different water levels (WL). We found that soil columns require considerably higher headspace CH2F2 concentrations for complete inhibition of CH4 oxidation than small soil samples. Inhibition remained complete until ca. 24 h after CH2F2 exposure. Then, the inhibitory effect diminished. The time needed for the inhibitory effect to disappear depended on WL; at a low WL of −15 cm, the inhibitory effect declined slowly and oxidation rates recovered by 90% only after 12 days. At WL = −5 cm, CH4 oxidation recovered much faster (90% recovery after ca. 3 days). Last, CH2F2 addition significantly decreased the N2O emissions, whereas CO2 emissions remained unaltered.