Temperature effects on soil methane production: an explanation for observed variability

Methane production in anaerobically incubated soil depends strongly on temperature. Reported values of Q10, which is the relative increase in activity after an increase in temperature of 10°C, are between 1.3 and 28. We attempted to explain this large variation by considering processes underlying methane production, namely anaerobic carbon mineralisation, reduction of alternative electron acceptors and increased methanogenic activity, each having a well accepted Q10 value of about 2. Q10 is hypothesised to vary due to a temperature-dependent lag time with alternative electron reduction before methane production starts (in incubation experiments). Slurried peat samples were incubated at 4, 10, 13.5, 20 and 30°C, and carbon dioxide, CH4 and fatty acids were intensively monitored for 98 d. The temperature dependence of anaerobic C-mineralisation could be described with Q10 values of 1.1 (4–13.5°C) and 1.5 (13.5–30°C). For other biological processes we assumed a common Q10 of 2. The experiment at 13.5°C was used to calibrate a temperature adapted version of a recently developed simulation model. This model was used to study the dynamic interactions of the temperature dependent subprocesses and simulated CH4 production at different temperatures reasonably well. At low temperatures, electron acceptors and methanogenic biomass limit methane production for a longer time leading to low methane production at low temperatures. This explains why the overall Q10 value calculated from both model (Q10 2–23) and experiment (Q10 2.9–3.6) varied in time and was larger than the Q10 values of the individual subprocesses (Q10 1.1–2). Some of the reported high overall Q10 values could be explained in the same way.