Regulation of methane production in a Swedish acid mire by pH, temperature and substrate

We analysed the effects of temperature, pH and glucose concentration on methane production from ombrotrophic Sphagnum-dominated hummocks, carpets and minerotrophic sedge fens, all sampled at two depths. The experiments were performed as slurry incubations and three variables, glucose concentration, temperature and pH, were varied according to a central composite design. The samples from the upper layers of sedge fen communities had the highest potential for methane production, samples from the upper layers of S. majus having about 70% and other samples 10–20% of this maximal potential. Methane production from the upper peat layers was substrate-limited in all three plant communities. The rate of methane production increased in samples from the carpet and mesotrophic fen when both substrate concentration and temperature were increased simultaneously. Variation of pH did not affect samples from the sedge fen, but methane production increased in samples from the S. majus carpet, and decreased in samples from the S. fuscum hummock when the pH was raised. Our results imply that the effects of temperature on methane production under field conditions are constrained by substrate limitation. However, the results of changing pH, stress the need to investigate the complex effects of pH on methane production in boreal mires.