To test the dose effect of ammonium (NH(4) (+)) fertilization on soil methane (CH(4)) oxidation by methanotrophic communities, batch incubations were conducted at a wide scale of NH(4) (+) amendments: 0, 100, 250, 500, and 1,000 mg N kg(dry soil) (-1). Denaturing gradient gel electrophoresis and real-time quantitative PCR analysis were conducted to investigate the correlation between the CH(4) oxidation capacity and methanotrophic communities. Immediately after the addition of NH(4) (+), temporal inhibition of CH(4) oxidation occurred, and this might have been due to the non-specific salt effect (osmotic stress). After a lag phase, the CH(4) oxidation rates of the soils with NH(4) (+) fertilization were promoted to levels higher than those of the controls. More than 100 mg N kg(dry soil) (-1) of NH(4) (+) addition resulted in the reduction of type II/type I MOB ratios and an obvious evolution of type II MOB communities, while less than 100 mg N kg(dry soil) (-1) of NH(4) (+) addition induced nearly no change of methanotrophic community compositions. The NH(4) (+)-derived stimulation after the lag phase was attributed to the improvement of N availability for type I MOB. Compared with the controls, 100 mg N kg(dry soil) (-1) of NH(4) (+) addition doubled the CH(4) oxidation peak value to more than 20 mg CH(4) kg(dry soil) (-1) h(-1). Therefore, an appropriate amount of leachate irrigation on the landfill cover layer might efficiently mitigate the CH(4) emissions.