Peat respiration at low temperatures

The peatlands of northern latitudes represent an enormous store of organic carbon. The decomposition of peat and the release of carbon dioxide is expected to increase with temperature as a result of climate change. CO2 emission and O2 uptake were measured during laboratory incubations of homogenised peat samples from 15 sites in Scotland. These were made either at fixed temperatures or in experiments where the temperature was steadily raised and lowered in 2°C steps, enabling Arrhenius plots to be made and the temperature response to be quantified as an activation energy or as a Q10. The respiratory quotient varied with temperature and this led to higher Q10 values for O2 uptake than for CO2 emission. Peats varied widely in their response to temperature; Q10 values were between 2.2 and 19 with a mean of 4.8. For most peats the response was approximately constant over the range of temperature tested but a third of the peats showed a marked deviation over the range 1–5°C where Q10 values increased considerably. Several published models describing the change in temperature response with temperature were applied to the data. A function in which the log of the soil respiration rate is a quadratic in temperature gave the best overall fit. Based on the observed laboratory Q10 values, a rise in mean annual temperature of 5°C could potentially increase CO2 emissions by a factor of 2- to 4-fold. For some peats at low temperatures (0–5°C) small changes in temperature could have a much more marked effect. This may be significant for the peatlands in Scotland and similar latitudes where soil temperatures are commonly within this range and where predicted temperature increases over the next 50 years may bring about a significant increase in peat decomposition rates.