Vegetation composition regulates the interaction of warming and nitrogen deposition on net carbon dioxide uptake in a boreal peatland

Abstract Peatlands are carbon sinks and have the potential to mitigate global warming. However, it is unclear whether peatlands will remain carbon sinks or switch to carbon sources under global changes, such as climate warming, elevated nitrogen (N) deposition and vegetation composition change. In this study, these global changes were mimicked in a boreal peatland for 7 years to explore the interactions of climate warming, elevated N deposition and vegetation composition on the carbon sink function of peatlands. The results showed that warming has a limited effect on net ecosystem production (NEP), while N addition decreased NEP by 65% owing to the detrimental effect on Sphagnum mosses. The negative impact of N addition on NEP could be mitigated by warming under intact vegetation. Under the treatment of graminoid removal, warming and elevated N addition (WN) decreased NEP by 80%–106%. Under the treatment of shrub removal, 7 years of WN treatment did not affect NEP. These results highlight the importance of vegetation composition in regulating net CO 2 flux in peatlands. If peatlands shift to shrub‐dominated ecosystems, the net CO 2 uptake in peatlands would be decreased under climate warming and elevated N deposition. If peatlands shift to graminoid‐dominated ecosystems, the net CO 2 uptake in peatlands would be unaltered under climate warming and elevated N deposition. This study sheds new light on the interactions of climate warming, elevated N deposition, and vegetation composition change on the CO 2 uptake of peatlands; and could help accurately evaluate the carbon sink function of peatlands under future global change. Read the free Plain Language Summary for this article on the Journal blog.