Kinetic model for methane oxidation by paddy soil as affected by temperature, moisture and N addition

The process of CH4 oxidation by a paddy soil incubated under an initial CH4 concentration of approximately 900 μl l−1 was simulated by a kinetic model, which assumed that the CH4 oxidation activity of soil, a product of the specific activity of the individual and the number of methanotropic bacteria, was dependent on the CH4 concentration during the incubation. The results showed that the model could very well simulate the process of CH4 oxidation by the paddy soil in a closed system. The simulated results implied that CH4 oxidation activity of the soil was induced at the beginning of the incubation, suggesting the growth of the methanotrophic bacterial community, then declined after reaching a peaked value. Additions of both NH4Cl and KCl not only significantly inhibited the initial special activity of the individual, but suppressed population growth as well. There was no significant difference of NH4Cl and KCl addition to inhibit the initial specific activity of the individual bacteria at the same added concentration, while NH4+ was more effective to suppress population growth than K+. The optimum temperature for CH4 oxidation by the paddy soil was about 35°C and the initial apparent activation energies varied from 59.7 to 159.1 kJ mol−1. The growth of methanotrophic bacteria almost ceased at temperatures above 40°C or below 12.5°C. The optimum water content for the soil to oxidize CH4 was 280 g kg−1, at which point, the specific activity of the individual bacteria was the highest and the increase in the oxidation activity was the fastest. The response of the CH4 oxidation activity to drying below the optimum was more sensitive than to wetting above the optimum. The prompt response of CH4 oxidation activity to elevated CH4 concentration and the decrease in sensitivity to wetting above the optimum moisture would be important for paddy soils to mitigate the emission of CH4 produced endogenously.