Methane uptake by cultivated Canadian prairie and forest soils

Abstract Global methane (CH 4 ) budgets depend on both CH 4 sources and sinks. We investigated CH 4 sink strength of cultivated Canadian prairie and forest soils using undisturbed soil columns and an incubation technique in the laboratory. The sink strength was estimated by determining the rate of CH 4 uptake by soils with variations in volume of air-filled soil voids, temperature and CH 4 concentration. CH 4 uptake was attributed to biologically mediated oxidation reactions since there was no significant CH 4 uptake by autoclaved soils. At field capacity moisture content and 24°C, CH 4 uptake under ambient atmosphere (2.4 μl CH 4 l −1 air) followed first-order kinetics, though this was not the case at a lower temperature (4°C). The rate constant (h −1 ) of first-order reaction of CH 4 uptake at 24°C was 0.1987 (Orthic Black Chernozemic), 0.0803 (Gray Luvisol, high C), 0.0210 (Gray Luvisol, low C), and 0.0091 (Saline Black Chernozemic). Relative to the reaction at 24°C, the percent reduction in amounts of CH 4 uptake at 4°C ranged from 49% (Orthic Black Chernozemic) to 80% (Saline Black Chernozemic). Increasing the volume of air-filled soil voids increased the rate of CH 4 uptake in the Orthic Black Chernozemic and the Gray Luvisol (high C) whereas it had little effect on the two other soils. The rate of the reaction was reduced by 30% (Saline Black Chernozemic) to 75% (Gray Luvisol, high C) when the reaction was initiated with higher CH 4 concentrations (12 and 30 μl l −1 ). Under these experiment conditions, a two-step process of CH 4 uptake also was observed, in which the first step was characterized by a fast CH 4 diffusion. These results contribute to the knowledge of relative importance of Canadian prairie and forest soils as a CH 4 sink and to the significance of local environmental factors in affecting the CH 4 sink strength.