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

Forest soils are an important sink for atmospheric CH(4) but the contribution of CH(4) oxidation, production and transport to the overall CH(4) flux is difficult to quantify. It is important to understand the role these processes play in CH(4) dynamics of forest soils, to enable prediction of how the size of this sink will respond to future environmental change. Methane oxidation, production and transport were investigated for a temperate forest soil, previously shown to be a net CH(4) consumer, to determine the extent to which physical and biological processes contributed to the not flux. The sum of oxidation 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 immediate inhibition Of CH(4) uptake on waterlogging soils, the findings suggested that soil CH(4) diffusion was an important regulator of CH(4) uptake. In support of this, a subsurface maximum for CH(4) oxidation was observed, but the exact depth of the maximum differed when rates were calculated on a mass or on an areal basis. Markedly varying potential CH(4) uptake activities between soil cores were masked in intact core rates. Potential CH(4) oxidation conformed well to Michaelis-Menten kinetics but V(max) K(t) and a(A)(O) values varied with depth, suggesting different functional methanotrophic communities 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 CH(4) mixing ratios atmospheric, as challenging soils with 20% CH(4) in air did not induce low-affinity oxidation kinetics. Atmospheric CH4 oxidation potentiaks exceeded production potentials by 10-220 times. The results show that the forest soil CH(4) flux was dominated by CH(4) oxidation and transport, methanogenesis played only a minor role. (C) 2001 Elsevier Science Ltd. All rights reserved.