Role of CH4 oxidation, production and transport in forest soil CH4 flux

Forest soils are an important sink for atmospheric CH4 but the contribution of CH4 oxidation, production and transport to the overall CH4 flux is diff icult to quantify. It is important to understand the role these processes p lay in CH4 dynamics of forest soils, to enable prediction of how the size o f this sink will respond to future environmental change. Methane oxidation, production and transport were investigated for a temperate forest soil, pr eviously shown to be a net CH4 consumer, to determine the extent to which p hysical and biological processes contributed to the not flux. The sum of ox idation rates for soil layers were significantly greater (P<0.05) than for the intact soil cores from which the layers were taken. Combined with the i mmediate inhibition Of CH4 uptake on waterlogging soils, the findings sugge sted that soil CH4 diffusion was an important regulator of CH4 uptake. In s upport of this, a subsurface maximum for CH4 oxidation was observed, but th e exact depth of the maximum differed when rates were calculated on a mass or on an areal basis. Markedly varying potential CH4 uptake activities betw een soil cores were masked in intact core rates. Potential CH4 oxidation co nformed well to Michaelis-Menten kinetics but V-max K-t and a(A)(O) values varied with depth, suggesting different functional methanotrophic communiti es were active in the profile, The presence of monophasic kinetics in fresh soil could not be used to infer that the soil was exposed only to CH4 mixi ng ratios atmospheric, as challenging soils with 20% CH4 in air did not ind uce low-affinity oxidation kinetics. Atmospheric CH4 oxidation potentiaks e xceeded production potentials by 10-220 times. The results show that the fo rest soil CH4 flux was dominated by CH4 oxidation and transport, methanogen esis played only a minor role. (C) 2001 Elsevier Science Ltd. All rights re served.