Fertilizer-induced fluxes dominate annual N2O emissions from a nitrogen-rich temperate fen rewetted for paludiculture

Abstract

Rewetted peatlands are weak to negligible sources of the greenhouse gas nitrous oxide (N2O). However, rewetted peatlands in use for paludiculture may require nitrogen (N) fertilization potentially creating hot moments for denitrification and N2O emissions. In this study, we measured N2O 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 N2O emissions were observed from all treatments after each fertilization event, which contributed to cumulative annual emissions of 3.2–6.0 kg N2O–N ha−1 in the first year and 1.8–4.2 kg N2O–N ha−1 in the second year. Emissions outside the fertilization periods were negligible. Annual N2O 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 N2O emissions can be high although background soil emissions are low when high GWT is maintained on N-rich riparian peatland.