Strong inhibitory effect of nitrate on atmospheric methane oxidation in forest soils

We investigated inhibitory effects of ammonium and nitrate on soil methane oxidation in two forests. Mineral soils in a forest with low nitrogen-deposition had much higher methane oxidation rates than those observed in nitrogen-saturated forest soils with higher nitrogen-deposition. Nitrate addition to soils from a low nitrogen-deposition site exhibited a stronger inhibitory effect on methane oxidation than either ammonium or potassium. The decrease in soil pH accompanied by the addition of nitrate was not responsible for this repression. Our results indicate that even a level of nitrate observed in N-saturated forests (dozens of μg N g soil−1) exerts a strong inhibitory effect on the oxidation of atmospheric methane, although the mechanism remains unresolved.