Characteristics of methane oxidation in a flooded rice soil profile

Laboratory experiments were conducted to study the variation of CH4 oxidation patterns in flooded rice soil profiles. The results indicated that surface soil presented the strongest CH4 oxidation activities as shown by the highest values of the two kinetic parameters of CH4 oxidation, V-max and K-m in the ecosystem without rice plants. V-max and K-m decreased significantly from top to bottom in the paddy rice soil profile, ranging from 12.5 to 1.2 mu g h(-1) g(-1) and 165 to 4.1 mu g g(-1), respectively. In addition, we studied the effect of headspace N-2, O-2 and their ratio on CH4 emission and oxidation to provide information on the sensitivity of methanogens and methanotrophs to soil redox change resulted from gas transportation through arenchyma. Methane emission rate increased, however, CH4 oxidation rate decreased with a decrease of O-2 concentration in the headspace. Headspace H-2 increased CH4 emission rate substantially. In addition to H-2 being a substrate for CH4 formation, the change of soil redox potential to a considerably low level H-2 should also contribute to the increase in CH4 emission.