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Dinitrogen and nitrous oxide formation in beech forest floor and mineral soils
No full textA (15)N tracer study was conducted to determine N(2) and N(2)O fluxes and the processes responsible for the formation of N(2)O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH=3.8) and the overlying acid forest floor (AFF) (pH=3.8) from the Soiling and a less acid mineral soil (LAM) (pH=5.2) from the Gottinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting (15)N. The evolved gases, N(2)O and N(2), and the ammonium and nitrate concentrations in the soils were measured together with the (15)N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N(2) at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N(2)O The N(2)O and N(2) emission calculated on an areal basis decreased from LAM, AFF, to AM. The N(2)O/(N(2)O+N(2)) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N(2)O. On prolonged incubation the N(2)O/(N(2)O+N(2)) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N(2) emissions to he 0.71 and 0.51 kg N ha(-1) yr(-1) for the Gottinger Wald and the Solling, using published annual in situ N(2)O emissions and our N(2)/N(2)O ratios. The in situ N(2)O emissions of the Gottinger Wald and Solling are 0.17 and 3 kg ha(-1) yr(-1) and the N(2) emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha(-1) yr(-1). The approach for estimating in situ N(2) emissions has to be improved in future studies
Dinitrogen and nitrous oxide formation in beech forest floor and mineral soils
No full textA (15)N tracer study was conducted to determine N(2) and N(2)O fluxes and the processes responsible for the formation of N(2)O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH=3.8) and the overlying acid forest floor (AFF) (pH=3.8) from the Soiling and a less acid mineral soil (LAM) (pH=5.2) from the Gottinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting (15)N. The evolved gases, N(2)O and N(2), and the ammonium and nitrate concentrations in the soils were measured together with the (15)N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N(2) at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N(2)O The N(2)O and N(2) emission calculated on an areal basis decreased from LAM, AFF, to AM. The N(2)O/(N(2)O+N(2)) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N(2)O. On prolonged incubation the N(2)O/(N(2)O+N(2)) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N(2) emissions to he 0.71 and 0.51 kg N ha(-1) yr(-1) for the Gottinger Wald and the Solling, using published annual in situ N(2)O emissions and our N(2)/N(2)O ratios. The in situ N(2)O emissions of the Gottinger Wald and Solling are 0.17 and 3 kg ha(-1) yr(-1) and the N(2) emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha(-1) yr(-1). The approach for estimating in situ N(2) emissions has to be improved in future studies
NOx and N2O fluxes in a nitrogen-enriched European spruce forest soil under experimental long-term reduction of nitrogen depositions
No full textEuropean 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. (c) 2012 Elsevier Ltd. All rights reserved.German Research Foundation [BR 1524/6-1
Contribution of nitrification and denitrification sources for seasonal N2O emissions in an acid German forest soil
No full textA N-15 tracer field experiment was carried out in an acid soil of a beech forest gap at the Solling area in Germany to determine the different formation processes of N2O. This site has been classified as a seasonal N2O emission type forest. Small amounts of highly enriched N-15 tracer were supplied separately as labelled NH4+ and NO3- seven times from May to October 1998. The N-15 compounds were injected with syringes into the upper 10 cm of the soil. The N2O emission showed a seasonal pattern with low emission in spring, high emission in summer, and low emission in autumn and followed the soil temperature. N2O was evolved only from the N-15-labelled NO3- pool in summer under field moist conditions, indicating that its formation was due to denitrification. In spring, early summer and autumn trapped NO or heterotrophic nitrification may also have been involved in N2O emission. (C) 2002 Elsevier Science Ltd. All rights reserved
Are Partial Nutrient Balances Suitable to Evaluate Nutrient Sustainability of Land use Systems? Results from a Case Study in Central Sulawesi, Indonesia
No full textThe fate of 15N-labeled nitrogen inputs to pot cultured beech seedlings
No full textThe partitioning of nitrogen deposition among forest soil (including forest floor), leachate and above- and belowground biomass of pot cultured beech seedlings in comparison to non-cultured treatments were investigated by adding 1.92 g·m-2 15N tracer in throughfall for two successive growing seasons at a greenhouse experiment. Ammonium and nitrate depositions were simulated on four treatments (cultured and non-cultured) and each treatment was labeled with either 15N-NH4 + or sN-NO3⎯. Total recovery rates of the applied 15N in the whole system accounted for 74.9% to 67.3% after 15N-NH4 + and 85.3% to 88.1% after 15N-NO3⎯ in cultured and non-cultured treatments, respectively. The main sink for both 15N tracers was the forest soil (including forest floor), where 34.6% to 33.7% of 15N-NH4 + and 13.1% to 9.0% of 15N-NO3⎯ were found in cultured and non-cultured treatments, respectively, suggesting strong immobilization of both N forms by heterotrophic microorganisms. Nitrogen immobilization by microorganisms in the forest soil (including forest floor) was three times higher when 15N-NH4 + was applied compared to 15N-NO3⎯. The preferential heterotrophic use of ammonium resulted in a two times higher retention of deposited 15N-NH4 + in the forest soil as compared to plants. In contrast, nitrate immobilization in the forest soil was lower compared to plants, although statistically it was not significantly different. In total the immobilization of ammonium in the plant-soil system was about 60% higher than nitrate, indicating the importance of the N-forms deposition for retention in forest ecosystems
Nitrous oxide emissions from soil during freezing and thawing periods
No full textIn a laboratory investigation, the processes of N2O emissions during freezing/thawing periods were studied. Four undisturbed soil columns from an agricultural site were subjected to two freeze/thaw cycles. Two periods of higher N2O emissions were detected, a period of elevated N2O emissions during continuous soil freezing and a period of brief peak emissions during thawing. Soil respiration indicated that microorganisms were still active in both periods. We concluded that N2O was produced by microorganisms during continuous soil freezing in an unfrozen water film on the soil matrix. This thin liquid water film was covered by a layer of frozen water. The frozen water in form of an ice layer represents a diffusion barrier which reduces oxygen supply to the microorganisms and partly prevents the release of the N2O. Peak emissions during soil thawing were explained by the physical release of trapped N2O and/or denitrification during thawing. (C) 2001 Elsevier Science Ltd. All rights reserved
Regulation of N2O and NOx emission patterns in six acid temperate beech forest soils by soil gas diffusivity, N turnover, and atmospheric NOx concentrations
Full text linkLow gas diffusivity of the litter layer is held responsible for high seasonal nitrous oxide (N2O) and low nitric oxide (NO) emissions from acid beech forest soils with moder type humus. The objectives were (i) to evaluate whether these beech forest soils generally exhibit high seasonal N2O emissions and (ii) to assess the influence of gas diffusivity and nitrogen (N) mineralisation on N oxide fluxes. We measured N2O and NOx (NO + NO2) fluxes in six German beech stands and determined net N turnover rates and gas diffusivity of soil samples taken at each chamber. High N2O emissions (up to 113 mu g N m(-2) h(-1)) were only observed at one beech stand. Net nitrification of the organic layer and soil gas diffusivity explained 77 % of the variation in N2O fluxes (P = 0.001). Fluxes of NOx were low (-6.3 to 12.3 mu g N m(-2) h(-1)) and appeared to be controlled by NOx concentrations in the forest air. Low soil gas diffusivity and high N turnover rates promoted high N2O losses in times of high soil respiration but were not necessarily associated with moder type humus. High seasonal emissions are probably less common in German beech forests than previously assumed.German Research Foundation [BR 1524/6
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