Potential aerobic methane oxidation in a Sphagnum-dominated peatland—Controlling factors and relation to methane emission

Abstract

The potential aerobic methane oxidation (an estimate of the viable biomass of methane-oxidizing microorganisms) was assessed in various plant communities of a boreal, Sphagnum-dominated, mixed mire in Sweden. The relationships between potential oxidation and probable controlling environmental factors, such as water table depth, soil temperature and pore-water methane concentrations were also examined. Finally, the relationship between potential methane oxidation and the rate of net methane emission was evaluated. Potential methane oxidation ranged between 0.0 and 4.7 μg CH 4 g −1 wet peat h −1, and the areal estimates for the 0–40 cm depth interval ranged between 0.04 and 16 g CH 4 m −2 d −1. The depth of maximal potential oxidation was correlated with the depth of the water table ( r 2 = 0.64). Most communities showed a positive relationship between average rate of potential methane oxidation and water table depth ( r 2 = 0.66), i.e. the greater the vertical extension of aerated surface peat, the higher the methane oxidation capacity. In non-waterlogged communities (water table more than 5 cm below the vegetation surface), a positive correlation was found between the potential oxidation and methane concentration in peat pore-water ( r 2 = 0.44). These results suggest that the supplies of methane and oxygen largely control the biomass of methanotrophs across plant communities. Overall, net methane emission rates were negatively, but only weakly, correlated with the potential oxidation, suggesting that aerobic oxidation often controls emission rates from comparatively dry communities of Sphagnum peatlands, but that other factors also influence the emission.