Methane oxidation kinetics differ in European beech and Norway spruce soils

Summary Coniferous forest soils often consume less of the greenhouse gas methane (CH 4 ) than deciduous forest soils. The reasons for this phenomenon have not been resolved. It might be caused by differences in the diffusive flux of CH 4 through the organic layer, pH or different concentrations of potentially inhibitory compounds. Soil samples were investigated from three adjacent European beech ( Fagus sylvatica ) and Norway spruce ( Picea abies ) stands in Germany. Maximal CH 4 oxidation velocities (V max(app) ) and Michaelis Menten constants (K M(app) ), retrieved from intact soil cores at constant CH 4 concentrations, temperature and matric potential, were twice as great in beech as in spruce soils. Also atmospheric CH 4 oxidation rates measured in homogenized soil samples displayed the same trend. Greatest atmospheric CH 4 oxidation rates were detected in the O a horizon or in the upper 5 cm of the mineral soil. In contrast to the beech soils, the O a horizon of the spruce soils consumed no CH 4 . A differential effect due to divergent diffusive flux through the litter layer was not found. pH and ammonium concentration were similar in samples from both forest soil types. Ethylene accumulation in all soils was negligible under oxic conditions. These collective results suggest that the different atmospheric CH 4 uptake by beech and spruce soils is caused by different CH 4 oxidizing capacities of methanotrophic communities in the O a horizon and top mineral soil.