Fertilizer-induced fluxes dominate annual N 2 O emissions from a nitrogen-rich temperate fen rewetted for paludiculture

Rewetted peatlands are weak to negligible sources of the greenhouse gas nitrous oxide (N 2 O). However, rewetted peatlands in use for paludiculture may require nitrogen (N) fertilization potentially creating hot moments for denitrification and N 2 O emissions. In this study, we measured N 2 O emissions from an N-rich riparian fen for two consecutive years using static chambers. The field experiment included side-by-side plots cultivated with reed canary grass ( Phalaris arundinacea L.) under different degrees of manipulated rewetting. The treatments were defined as control, semi-flooded and flooded conditions corresponding to 2-year weighted mean groundwater table (GWT) depths of 9, 3 and 1 cm below soil surface, respectively. The crop was fertilized and harvested twice a year (160 kg N ha −1 year −1 in two equal splits). Large N 2 O emissions were observed from all treatments after each fertilization event, which contributed to cumulative annual emissions of 3.2–6.0 kg N 2 O–N ha −1 in the first year and 1.8–4.2 kg N 2 O–N ha −1 in the second year. Emissions outside the fertilization periods were negligible. Annual N 2 O emissions were similar ( P > 0.05) among the treatments in the first year whereas control treatments had the lowest emissions in the second year. Nitrogen removal in harvested biomass (197–218 kg N ha −1 year −1 ) exceeded the fertilizer N in all treatments, indicating that the cultivated biomass utilized substantial amounts of mineralized N from the peat soil. Overall, the results indicate that fertilizer-induced N 2 O emissions can be high although background soil emissions are low when high GWT is maintained on N-rich riparian peatland.