Effect of soil types and ammonia concentrations on the contribution of ammonia-oxidizing bacteria to CH oxidation.

Irrigation of stabilized landfill leachate to landfill cover soil is a cost-effective operation for leachate treatment. The contribution of ammonia-oxidizing bacteria (AOB) in the cover soil to CH oxidation, however, is unclear, because AOB and methane-oxidizing bacteria (MOB) can co-oxidize CH and NH-N. Thus, the contribution of AOB and the inhibitory effect of NH-N to CH oxidation were determined by using an acetylene pretreatment discrimination method. The results showed that the contributions of AOB to CH oxidation varied with the soil type and the concentration of NH-N addition. The relative contribution of AOB to CH oxidation for compost without NH-N addition was the highest (65.0%), and was 2.5 and 3.4 times higher than the corresponding values for aged refuse and landfill cover soil, respectively. The inhibitory effect of NH-N was enhanced by increasing the concentration of NH-N addition for all the soil samples. At equal NH-N addition concentrations, the inhibitory effect was always the lowest for the compost sample. The abundances of particulate methane monooxygenase () and ammonia monooxygenase () genes were key factors influencing the CH oxidation rate and contribution of AOB to CH oxidation. The higher abundance of and lower abundance of in landfill cover soil could explain the higher CH oxidation rate and lower contribution of AOB to CH oxidation in this soil type. Meanwhile, the higher contribution of AOB to CH oxidation for compost could be attributed to the higher abundance of the gene and lower abundance of .