Microbial Carbon Mineralisation in an Acid Surface Peat: Effects of Environmental Factors in Laboratory Incubations

The regulation of terminal carbon mineralisation in an acid surface peat dominated by Sphagnum majus, from a boreal mire was studied in laboratory incubations. A factorial design at two levels were used, with the factors and settings in two different experiments as follows: temperature (7°C, 17°C; 15°C, 25°C), pH (4.3, 6.2; 4.3, 6.8), substrate (none, starch, glucose; none, glucose). Using 13C NMR spectroscopy we found that both aerobic and anaerobic degradation of 13C-U-glucose were restricted by the low native pH (4.3) compared with experimentally increased pH (6.8) in the S. majus peat. The factors included in the statistical models of the rates of CH4 production for experiment I and II explained 98% and 74% of the variation, and the predictive ability of these models was 95% and 63%, respectively. The statistical models for the rate of CO2 production for series I and II explained 78% and 81% of the variation, and the predictive ability was 64% and 60%, respectively. In both experiments an increase in temperature from either 7 to 17°C or from 15 or 25°C increased the rates of CH4 production with approximately 60 nmol g−1 dw h−1. This temperature effect was approximately 3-fold larger than the effect of adding 10 mM glucose in experiment I, but equal to the addition of glucose in experiment II. Addition of starch, in amounts equal to 10 mM glucose-C, increased the rates of CH4 production with 12 nmol g−1 dw h−1, suggesting that the anaerobic degradation of polymers per se is not restricted in the surface peat studied. The rates of CH4 production decreased with approximately 20 nmol g−1 dw h−1, when the pH increased from 4.3 to 6.2 or 6.8, probably due to the accumulation of toxic, undissociated volatile fatty acids. Increased temperature had a weaker effect on the rates of CO2 production than on CH4 production from the surface peat. Carbon dioxide production rates from the S. majus surface peat were higher under aerobic than under anaerobic conditions, with the average aerobic: anaerobic quotient being 4.3 (S.D.=3.1).