Methane oxidation in a temperate coniferous forest soil: effects of inorganic N

Abstract

Methane oxidation rates were measured in soils obtained from a coniferous forest in northern England. The effects of depth and added K + (K 2SO 4), NH 4 + ((NH 4) 2SO 4) and NO 3 − (KNO 3) on potential CH 4 oxidation were investigated in a series of laboratory incubations. The humus (H) layer soil showed much greater CH 4 oxidation rates than the other soil layers, with maximal rates of 53 and 226 ng CH 4 gdw −1 h −1 when incubated with initial 10 and 1000 μl CH 4 l −1, respectively. Additions of the solutes K +, NH 4 + and NO 3 − showed differing degrees of inhibition on CH 4 oxidation, which varied with the initial CH 4 concentration, the ion added, and the ion concentration. In general, inhibition by the ions was slightly greater for incubations with an initial concentration of 1000 μl CH 4 l −1 than for 10 μl CH 4 l −1 under otherwise identical conditions. For K + and NH 4 + treatments, inhibitory rates were usually less than 15%, but at high K + and NH 4 + concentrations inhibition could reach 50%, the inhibitory effects of NH 4 + were consistently slightly greater than those of K + at the same concentration. In marked contrast to NH 4 +, NO 3 − showed a very strong inhibitory effect. Added NO 3 − and NO 2 − produced via added NO 3 − reduction in anaerobic ‘microsites’ are probably toxic to CH 4-oxidizing bacteria. These results, together with those from other reports, suggest that NO 3 − may have a greater importance in the inhibition of CH 4 oxidation in forest soils than that attributed to NH 4 + and needs to be investigated in a wide range of soil types from various forests.