The responses of soil methane (CH4) net fluxes to nitrogen (N) addition in a N-fixing tree species ( Acacia auriculiformis ( AA )) and a non-N-fixing tree species ( Eucalyptus citriodora ( EU )) plantation were studied in southern China. Treatments were conducted at each plantation with three N levels (0, 50, and 100 kg N ha−1 yr−1 for control, medium-N, and high-N treatment, respectively, abbreviated as C, MN, and HN). From August 2010 to July 2011, CH4 flux was measured biweekly using a static chamber and gas chromatography technique.