Methane and Carbon Dioxide Dynamics in a Northern Hardwood Ecosystem

There is evidence that oxidation of CH 4 to CO 2 by methanotrophic bacteria in forest soil is a major sink for atmospheric CH 4 , even though growth of the bacteria on such low CH 4 concentrations (<1.7 µL L −1 ) is perplexing. Measurements of CH 4 and CO 2 in a northern hardwood ecosystem in the Adirondack Park in the state of New York indicated that: (i) soil CH 4 concentrations were mostly higher than the concentration of CH 4 in forest air, with concentrations as high as 500 µL L −1 at the 0.1‐m depth in the early and late parts of the growing season; (ii) soil CO 2 concentrations ranged from the atmospheric level to as high as 19 000 µL L −1 at the 0.2‐m depth in midsummer; (iii) net consumption of atmospheric CH 4 emission by soil in midsummer averaged only 0.25 mg m −2 d −1 , which is low compared with findings for most forest ecosystems; and (iv) methanogenesis occurred in soil samples throughout the profile when incubated anaerobically as well as aerobically with CH 3 F to inhibit methanotrophs. The prominent activity of methanogenic bacteria producing CH 4 in the spring and autumn could support the growth of methanotrophic bacteria that otherwise consume atmospheric CH 4 when methanogens are not active. Therefore, CH 4 dynamics in this Spodosol represent the balance between CH 4 production and CH 4 oxidation, which is similar to the CH 4 dynamics in many wetland ecosystems.