科研之友
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摘要
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 Soiling 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.
- 出版日期2012-12
