Nitrogen addition (NH4NO3) mitigates the positive effect of warming on methane fluxes in a coastal bog.

• Warming significantly increased CH 4 emission by 52%. • N addition reduced the positive effect of warming on CH 4 flux. • Warming and N addition together did not significantly change CH 4 flux. • CH 4 flux positively correlated with GPP. • Soil T, soil moisture, DOC and TN were the main controls for CH 4 flux. Methane (CH 4) fluxes in boreal peatlands could be impacted by global warming and N deposition. However, the interaction of these factors remains poorly understood and has not been considered in coupled climate-carbon models. In this study, manipulated warming and N deposition (ammonium nitrate) were conducted for five years in a coastal bog in western Newfoundland, Canada. Consistent with previous studies, warming significantly increased CH 4 emission by 52%, which might be due to the increase of microbial activity and vegetation growth. Although N addition alone did not alter CH 4 emissions, it significantly reduced the positive effect of warming on CH 4 fluxes. We attributed this finding to three possible reasons: (1) N addition caused a shift in root allocation from deep to shallow roots, which decreased labile substrates for CH 4 production under warming; (2) warming promoted vegetation uptake of ammonium (NH 4 +), which alleviated the inhibition of NH 4 + to methanotrophs and subsequently increased CH 4 oxidation under N addition; and (3) the combination of warming and N addition increased maintenance respiration of vascular plants compared with warming alone, thus reducing net primary production and root exudates for CH 4 production. In addition, we found that soil temperature, soil moisture, DOC and TN were the main controls on CH 4 fluxes. Our results indicate that the combined effect of N deposition and warming should not be ignored. Otherwise, the emission of CH 4 in bogs will be overestimated under future scenarios of climate warming and N deposition increase. Our study can be further applied as empirical evidence for the parameterization of temperature-dependence and nutrient-dependence of CH 4 fluxes in biogeochemical models of boreal peatlands. [ABSTRACT FROM AUTHOR]