Methane oxidation in temperate soils: effects of inorganic N

Additions of inorganic nitrogen (N) to an oak soil with significant potential for methane (CH4) oxidation resulted in differential reduction in CH4 oxidation capacity depending on N species added. Nitrate, rather than nitrite or ammonium, proved to be the strongest inhibitor of CH4 oxidation in oak soil. Both high (CH4 at 10 μl l−1) and low (CH4 at 5 ml l−1) affinity CH4 oxidation in oak soil was completely inhibited at a nitrate concentration similar to that present in an alder soil from the same experimental site. The alder soil showed no capacity for low affinity CH4 oxidation. A ‘low nitrate’ forest soil (oak) showed high affinity, low capacity CH4 oxidation upto around 1 ml l−1 CH4, above which both high and low affinity CH4 oxidation became apparent following a lag phase, indicating either an induced high affinity uptake mechanism or the existence of distinct low affinity and high affinity methanotroph populations. High affinity CH4 oxidation became saturated at CH4 concentrations >500 μl l−1, while low affinity CH4 oxidation became saturated at ∼30 ml l−1 CH4. In a ‘high nitrate’ forest soil (alder), CH4 oxidation appeared to be due to high affinity CH4 oxidation only and became undetectable at CH4 concentrations >5 ml l−1.