Nitrogen (N) deposition has been increasingly severe in global change, which had an important impact on various processes of forest ecosystems. Evaluating the effects of N addition on the output of soil carbon (C) in forest ecosystems was important for estimating the soil C sequestration to global change. A two-year N addition experiment was conducted with four different N addition levels, including the control (CK, 0 kg N hm^-2 a^-1), low N addition (LN, 50 kg N hm^-2 a^-1), medium N addition (MN, 100 kg N hm^-2 a^-1) and high N addition (HN, 150 kg N hm^-2 a^-1) levels, in four forests with different tree species compositions (i.e., Betula platyphylla, Fraxinus mandschurica, Pinus koraiensis, and Larix olgensis) in Maoershan Experimental Station of Heilongjiang Province. Root biomass density, soil microbial biomass C concentration, soil respiration rate, temperature and humidity sensitivity were measured to evaluate the responses of the soil respiration to N addition. (1) The soil respiration rate in P. koraiensis and L. olgensis stands increased significantly under LN treatment, while that were not affected in B. platyphylla and F. mandschurica stands. Compared with LN and MN treatments, the soil respiration rate under HN treatment were decreased significantly in F. mandschurica stand. The soil respiration rate under HN treatment was significantly lower than that of LN treatment in other stands. (2) The soil respiration rate was significantly positive correlation with root biomass density under N addition treatments. The Pearson's correlation coefficient was 0.81. (3) Compared with the CK treatment, the soil temperature sensitivity coefficients (Q10) in the depth of 5 cm and 10 cm were increased by 2.65% and 3.12% under LN treatment, but that were decreased by 6.29% and 5.46% under HN treatment, respectively. But the soil respiration was not significantly correlated with the soil humidity after N addition. Thus the responses of the soil respiration of broad-leaved and coniferous forests were different after N addition. The root biomass density was the main factor affecting the responses of the soil respiration in different forests after short-term N addition. The soil temperature sensitivity coefficient was changed significantly by N addition treatments.