Effects of Elevated CO(2) and Nitrogen Deposition on Ecosystem Carbon Fluxes on the Sanjiang Plain Wetland in Northeast China

BACKGROUND: Increasing atmospheric CO(2) and nitrogen (N) deposition across the globe may affect ecosystem CO(2) exchanges and ecosystem carbon cycles. Additionally, it remains unknown how increased N deposition and N addition will alter the effects of elevated CO(2) on wetland ecosystem carbon fluxes. METHODOLOGY/PRINCIPAL FINDINGS: Beginning in 2010, a paired, nested manipulative experimental design was used in a temperate wetland of northeastern China. The primary factor was elevated CO(2), accomplished using Open Top Chambers, and N supplied as NH(4)NO(3) was the secondary factor. Gross primary productivity (GPP) was higher than ecosystem respiration (ER), leading to net carbon uptake (measured by net ecosystem CO(2) exchange, or NEE) in all four treatments over the growing season. However, their magnitude had interannual variations, which coincided with air temperature in the early growing season, with the soil temperature and with the vegetation cover. Elevated CO(2) significantly enhanced GPP and ER but overall reduced NEE because the stimulation caused by the elevated CO(2) had a greater impact on ER than on GPP. The addition of N stimulated ecosystem C fluxes in both years and ameliorated the negative impact of elevated CO(2) on NEE. CONCLUSION/SIGNIFICANCE: In this ecosystem, future elevated CO(2) may favor carbon sequestration when coupled with increasing nitrogen deposition.