Soil respiration plays a crucial role in global carbon cycling of terrestrial ecosystems. Changes in atmospheric CO₂ and nitrogen (N) addition across the globe are likely to affect soil respiration. However, the effects of elevated CO₂, and N addition on soil respiration are not fully understood especially in wetland ecosystems. To evaluate the effects of atmospheric CO₂ and N availability on soil respiration, a paired, nested manipulative in situ experiment was performed, using CO₂ fumigation within Open-Top Chambers as the primary factor, and N (as NH₄NO₃) as the secondary factor in a temperate wetland in northeastern China in 2010 and 2011. CO₂ fumigation significantly enhanced soil respiration, according to repeated-measures ANOVA, and the stimulatory effect of CO₂ fumigation on soil respiration was sustained during the whole experimental period regardless of N addition. However, the positive soil respiration effect of N addition alone weakened over time. Moreover, there was a significant interaction between CO₂ fumigation and N addition. Soil temperature explained 50–66% of the variation in soil respiration. Moreover, soil respiration was positively correlated with the root N content and litter decomposition rate. The results suggested that elevated CO₂ concentrations will accelerate soil respiration and ecosystem carbon cycling, thus, limiting soil carbon sequestration, especially when coupled with increasing N deposition.