Several studies have shown that increasing nitrogen deposition affects methane uptake in the forest ecosystems; however, the microbial mechanisms underlying this phenomenon remain unclear. In the present study, the seasonal variation in methanotroph abundance and community structure in a temperate forest receiving long-term differential nitrogenous compound addition treatments (45 kg N hm^-2 a^-1 using (NH₄)₂SO₄, NH₄Cl, and KNO₃) in Changbai mountains, were investigated by using real-time PCR, cloning, and sequencing. Methanotroph pmoA gene abundances were similar among all fertilized and control plots in summer (1.54×10⁶-3.20×10⁶ copies g^-1 dry soil); however, in fall, it was significantly lower in the (NH₄)₂SO₄ treatment (4.61×10⁵±2.61×10⁵ copies g^-1 dry soil) than that in the control plots (4.03×10⁶±1.2×10⁶ copies g^-1 dry soil). In both summer and fall, the methanotroph community was dominated by Type I methanotrophs, consisting of Methylobacter-group (Type I) and Methylococcus-group (Type I), with the relative abundance varying from 70.6%-85.4%. The dominant clade of Type I methanotroph, Methylobacter-group (Type I) showed no significant variance among all treatments in summer, but were present in significantly lower proportions in the (NH₄)₂SO₄ (52.7%±6.5%) and NH₄Cl (56.1%±8.9%) treatments than in the control in fall. In contrast, Methylococcus-group (Type I) showed an increasing trend in the (NH₄)₂SO₄ and NH₄Cl treatments compared to that in the control plots in fall. Overall, these results suggested that the addition of NH₄⁺-N fertilizers could inhibit the growth of methane oxidizing bacteria, and change their community composition. The inhibition effect became more obvious in fall than in summer, owing to the interactive effects of soil moisture and temperature in summer, whereas NO₃^--N addition showed no significant effect on the abundance and community composition of methanotrophs. These results were consistent with the previous observation that ammonium-based fertilizer addition reduced methane uptake from temperate forest soil in fall rather than in summer, and provided insights into the microbial mechanisms driving methane uptake in temperate forests under long-term nitrogen addition treatments.