Kombinierte Anwendung der natürlichen Häufigkeit stabiler Isotope und der 15N- Markierungstechnik für die Quantifizierung der Denitrifikation in landwirtschaftlichen Böden in Feldstudien
Zusammenfassung der Projektergebnisse
Quantifying denitrification in arable soils is crucial in predicting the microbial consumption of nitrogen fertilizers and the associated nitrous oxide (N2O) emissions, but still challenging due to difficulties in direct measurements of dinitrogen (N2) emissions and due to possible co-existence of numerous soil microbial N-transformations. In this project I developed the method for quantification of N2O reduction based on the isotopomer analyses of emitted N2O (δ15N, δ18O and SP = Site Preference of 15N within the linear N2O molecule). It was tested how well this method is able to distinguish N2O production pathways and to quantify N2O reduction to N2. Particularly, it was investigated: (i) how to determine the isotopic fractionation factors in laboratory experiments, (ii) how to transfer the laboratory results into field conditions, (iii) how to validate these results with independent analytical methods. This project combined laboratory and field studies to obtain information on the possible transferability of the methods developed under laboratory conditions to the field scale. A method for in situ quantification of the entire denitrification process in agricultural soils has been proposed, validated and applied in practical field studies. The developed method is solely based on the natural abundance stable isotope approach, i.e., combined isotopomer analyses of N2O and isotopic analyses of soil N-compounds. To precisely determine the isotopic fractionation factors associated with denitrification and possible accompanying processes valid for field conditions, detailed microcosm experiments under controlled conditions and accompanied by 15N tracing as a reference method were conducted. The fractionation factors associated with N2O reduction were validated for field conditions through direct determination of the product ratio of denitrification (N2O/(N2+N2O)) from 15N tracing results obtained parallel to N2O isotopomer analyses. Additionally, the analysis of natural abundance isotopic signatures of soil nitrite were conducted for the first time in order to better assess the process dynamics of this crucial compound in N-cycling. A practical result of this project is: (i) development of N2O isotope model based simultaneously on three N2O isotopic signatures (δ15N, δ18O and SP) which allows for differentiation of N2O production pathways and quantification of N2O reduction, and (ii) development of soil nitrite isotope model allowing for tracing soil N-transformations and estimation of their rates.
Projektbezogene Publikationen (Auswahl)
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Oxygen isotope fractionation during N2O production by soil denitrification. Biogeosciences 13, 1129-1144
Lewicka-Szczebak, D., Dyckmanns, J., Kaiser, J., Marca, A., Augustin, J. and Well, R.
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Quantifying N2O reduction to N2 based on N2O isotopocules - validation with independent methods (helium incubation and 15N gas flux method). Biogeosciences, 14, 711-732, 2017
Lewicka-Szczebak, D., Augustin, J., Giesemann, A., and Well, R.
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The nitrogen cycle: A review of isotope effects and isotope modeling approaches, Soil Biology and Biochemistry, 105, 121-137, 2017
Denk, T. R. A., Mohn, J., Decock, C., Lewicka-Szczebak, D., Harris, E., Butterbach-Bahl, K., Kiese, R., and Wolf, B.
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Estimating N2O processes during grassland renewal and grassland conversion to maize cropping using N2O isotopocules, Rapid Commun Mass Sp, 32 (13), 1053-1067, 2018
Buchen, C., Lewicka‐Szczebak, D., Flessa, H., and Well, R.
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N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction – validation with 15N gas-flux method in laboratory and field studies, Biogeosciences 17, 5513-5537, 2020
Lewicka-Szczebak, D., Lewicki, M. P., and Well, R.
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The 15N gas-flux method to determine N2 flux : a comparison of different tracer addition approaches, SOIL, 6, 145-152, 2020
Lewicka-Szczebak, D. and Well, R.
