Temperature sensitivity of anaerobic methane oxidation versus methanogenesis in paddy soil: Implications for the CH<sub>4</sub> balance under global warming
Lichao Fan, Michaela A. Dippold, Volker Thiel, Tida Ge, Jinshui Wu, Yakov Kuzyakov, Maxim Dorodnikov
Abstract
Abstract The global methane (CH 4 ) budget is based on a sensitive balance between methanogenesis and CH 4 oxidation (aerobic and anaerobic). The response of these processes to climate warming, however, is not quantified. This largely reflects our lack of knowledge about the temperature sensitivity ( Q 10 ) of the anaerobic oxidation of CH 4 (AOM)—a ubiquitous process in soils. Based on a 13 CH 4 labeling experiment, we determined the rate, Q 10 and activation energy of AOM and of methanogenesis in a paddy soil at three temperatures (5, 20, 35°C). The rates of AOM and of methanogenesis increased exponentially with temperature, whereby the AOM rate was significantly lower than methanogenesis. Both the activation energy and Q 10 of AOM dropped significantly from 5–20 to 20–35°C, indicating that AOM is a highly temperature‐dependent microbial process. Nonetheless, the Q 10 of AOM and of methanogenesis were similar at 5–35°C, implying a comparable temperature dependence of AOM and methanogenesis in paddy soil. The continuous increase of AOM Q 10 over the 28‐day experiment reflects the successive utilization of electron acceptors according to their thermodynamic efficiency. The basic constant for Q 10 of AOM was calculated to be 0.1 units for each 3.2 kJ mol −1 increase of activation energy. We estimate the AOM in paddy soils to consume 2.2~5.5 Tg CH 4 per year on a global scale. Considering these results in conjunction with literature data, the terrestrial AOM in total consumes ~30% of overall CH 4 production. Our data corroborate a similar Q 10 of AOM and methanogenesis. As the rate of AOM in paddy soils is lower than methanogenesis, however, it will not fully compensate for an increased methane production under climate warming.