Soil methane oxidation in both dry and wet temperate eucalypt forests shows a near-identical relationship with soil air-filled porosity

Well-drained, aerated soils are important sinks foratmospheric methane (CH4) via the process of CH4 oxidationby methane-oxidising bacteria (MOB). This terrestrialCH4 sink may contribute towards climate change mitigation,but the impact of changing soil moisture and temperatureregimes on CH4 uptake is not well understood inall ecosystems. Soils in temperate forest ecosystems are thegreatest terrestrial CH4 sink globally. Under predicted climatechange scenarios, temperate eucalypt forests in southeasternAustralia are predicted to experience rapid and extremechanges in rainfall patterns, temperatures and wildfires. To investigate the influence of environmental driverson seasonal and inter-annual variation of soil–atmosphereCH4 exchange, we measured soil–atmosphere CH4 exchangeat high-temporal resolution (−1) and in a wet temperature eucalypt forestin Tasmania (Warra Long-Term Ecological Researchsite, 1700 mm yr−1). Both forest soil systems were continuousCH4 sinks of −1.79 kg CH4 ha−1 yr−1in Victoriaand −3.83 kg CH4 ha−1 yr−1in Tasmania. Soil CH4 uptakeshowed substantial temporal variation and was strongly controlledby soil moisture at both forest sites. Soil CH4 uptakeincreased when soil moisture decreased and this relationshipexplained up to 90 % of the temporal variability. Furthermore,the relationship between soil moisture and soil CH4flux was near-identical at both forest sites when soil moisturewas expressed as soil air-filled porosity (AFP). Soil temperatureonly had a minor influence on soil CH4 uptake. Soil nitrogenconcentrations were generally low and fluctuations innitrogen availability did not influence soil CH4 uptake at eitherforest site. Our data suggest that soil MOB activity in thetwo forests was similar and that differences in soil CH4 exchangebetween the two forests were related to differences insoil moisture and thereby soil gas diffusivity. The differencesbetween forest sites and the variation in soil CH4 exchangeover time could be explained by soil AFP as an indicator ofsoil moisture status