Response of methanotrophs and methane oxidation on ammonium application in landfill soils

To test the dose effect of ammonium (NH4 (+)) fertilization on soil methane (CH4) oxidation by methanotrophic communities, batch incubations were conducted at a wide scale of NH4 (+) 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 CH4 oxidation capacity and methanotrophic communities. Immediately after the addition of NH4 (+), temporal inhibition of CH4 oxidation occurred, and this might have been due to the non-specific salt effect (osmotic stress). After a lag phase, the CH4 oxidation rates of the soils with NH4 (+) fertilization were promoted to levels higher than those of the controls. More than 100 mg N kg(dry soil) (-1) of NH4 (+) 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 NH4 (+) addition induced nearly no change of methanotrophic community compositions. The NH4 (+)-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 NH4 (+) addition doubled the CH4 oxidation peak value to more than 20 mg CH4 kg(dry soil) (-1) h(-1). Therefore, an appropriate amount of leachate irrigation on the landfill cover layer might efficiently mitigate the CH4 emissions.