NOₓ and N₂O fluxes in a nitrogen-enriched European spruce forest soil under experimental long-term reduction of nitrogen depositions
2012
Eickenscheidt, Nadine | Brumme, Rainer
European temperate forest soils have been exposed to elevated nitrogen (N) and acid depositions for decades. High nitrous oxide (N₂O) and nitric oxide (NO) emissions have been reported from these forests. Since the 1980s, a decline in atmospheric deposition rates has been occurring. Our study addressed the question as to how N oxide fluxes and N turnover processes have changed in response to the declining N depositions in a N-enriched spruce stand (Picea abies (L.) Karst.). Studies were conducted at the Solling roof site under a control-roof with ambient depositions and under a reduced-N-input-roof where N and acid depositions have been reduced to a pre-industrial level for 16–17 years. Open dynamic and closed chamber methods were used to determine NOₓ and N₂O fluxes, respectively, and in situ incubation studies were conducted to measure net N mineralisation. Under the reduced deposition roof, net nitrification and nitrate in soil solution were reduced to undetectable levels causing the soil to change from a net source for NOₓ (0.62 ± 0.24 kg N ha⁻¹ yr⁻¹) into a net sink (−0.33 ± 0.01 kg N ha⁻¹ yr⁻¹). The uptake of NOₓ was exclusively controlled by the NOₓ concentrations of the forest air. Reversal of N enrichment did not affect annual N₂O fluxes (0.08 kg N ha⁻¹ yr⁻¹) due to restricted denitrification in the well-aerated organic layer, but the origin of nitrate for denitrification changed from mainly soil-borne N to exclusively deposited N. It was demonstrated that less than two decades of reduced N and acid depositions are sufficient to reduce the surplus N and NOₓ emissions of this soil.
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