Effect of tree species on methane and ammonium oxidation capacity in forest soils

High and low affinity methane oxidation potentials were measured for soils under five fully replicated land-use treatments over an entire calendar year. Simultaneous measurements of soil nitrification potential in replicate soil samples were also made. Both high and low affinity CH4 oxidation were significantly reduced in the nitrate-rich soils under alder, compared to the other four vegetation treatments (oak, Norway spruce, Scots pine and grass). However, the effect of land-use was less for high affinity methanotrophy than for low affinity CH4 oxidation. Nitrification rates were highest in alder soils, with the greatest potential for NH4+ oxidation occurring in the top 5 cm of the soil. No significant relationship between potential nitrification rate and low affinity CH4 oxidation was seen. However, a significant negative relationship between nitrification and high affinity CH4 oxidation was identified. We found vegetation type to be a key determinant of soil-mediated CH4 and NH4+ oxidation, but found no evidence for significant CH4 oxidation by nitrifying bacteria.