Interactive effects of nitrate and oxygen on methane oxidation in three different soils

The ability of soil to uptake methane is regulated by several factors affecting soil microbial activity. The soil oxygen concentration is usually lower than the concentration of atmospheric air, and nitrogen fertilization contributes to a significant increase in nitrate-N in soil. Therefore, we selected three agricultural soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol) to investigate interactive effects of oxygen and nitrate (KNO3) on CH4 oxidation including different gradients of O-2 (20%, 10%, 5%, 2%) and nitrate (0, 100, 200 mg N kg(-1)). The soils varied in their response to O-2 and nitrate treatments. In the absence of nitrate, all soils completely oxidized added CH4 (1%) under the oxygen concentrations used (except 2%O-2); however, low oxygen (5%; 10%O-2) was optimal. Both nitrate doses strongly stimulated methane oxidation at 2%O-2 in Podzol and Gleysol, but generally inhibited CH4 uptake in Cambisol.