Effects of CO2 Fumigation and Nitrogen Addition on Soil Respiration in a Wetland Ecosystem: Experimental Approach with Top Open Chambers

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.