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| Titel |
Estimating N2O processes during grassland renewal and grassland conversion to maize cropping using N2O isotopocules |
| VerfasserIn |
Caroline Buchen, Reinhard Well, Heinz Flessa, Roland Fuß, Mirjam Helfrich, Dominika Lewicka-Szczebak |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141307
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| Publikation (Nr.) |
 EGU/EGU2017-4805.pdf |
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| Zusammenfassung |
| Grassland break-up due to grassland renewal and grassland conversion to cropland can lead to
a flush of mineral nitrogen from decomposition of the old grass sward and the decomposition
of soil organic matter. Moreover, increased carbon and nitrogen mineralisation can result in
enhanced nitrous oxide (N2O) emissions. As N2O is known to be an important greenhouse
gas and a major precursor for ozone depletion, its emissions need to be mitigated by adjusting
agricultural management practices. Therefore, it is necessary to understand the N2O
processes involved, as well as the contribution of N2O reduction to N2. Apart from the widely
used 15N gas flux method, natural abundance isotopic analysis of the four most abundant
isotopocules of N2O species is a promising alternative to assess N2O production
pathways.
We used stable isotope analyses of soil-emitted N2O (δ18ON2O, δ15NN2Obulk and
δ15NN2OSP= intramolecular distribution of 15N within the linear N2O molecule) with an
isotopocule mapping approach to simultaneously estimate the magnitude of N2O
reduction to N2 and the fraction of N2O originating from the bacterial denitrification
pathway or fungal denitrification and/or nitrification. This approach is based on
endmember areas of isotopic values for the N2O produced from different sources
reported in the literature. For this purpose, we calculated two main scenarios with
different assumptions for N2O produced: N2O is reduced to N2 before residual N2O is
mixed with N2O of various sources (Scenario a) and vice versa (Scenario b). Based
on this, we applied seven different scenario variations, where we evaluated the
range of possible values for the potential N2O production pathways (heterotrophic
bacterial denitrification and/or nitrifier denitrification and fungal denitrification and/or
nitrification). This was done by using a range of isotopic endmember values and assuming
different fractionation factors of N2O reduction in order to find the most reliable
scenario. Investigations were carried out over a study period of one year following
grassland renewal and grassland conversion to maize cropping on two different
soil sites (Plaggic Anthrosol and Histic Gleysol) near Oldenburg, Lower Saxony
Germany.
Our observations indicate heterotrophic bacterial denitrification and/or nitrifier
denitrification as the main source of N2O production, with a significant contribution of N2O
reduction to N2 rather than nitrification (i.e. hydroxylamine oxidation) and fungal
denitrification throughout the entire study period. A tendency to a higher contribution of N2O
reduction to N2 was observed for the often water-saturated Histic Gleysol, while lower N2O
reduction was found for the Plaggic Anthrosol. For two samples, we attempt to validate our
results from the isotopocule mapping approach with a parallel 15N labelling study at the field
scale (Buchen et al., 2016), as conditions of soil moisture, nitrate availability and N2O flux
were similar.
References:
Buchen, C., Lewicka-Szczebak, D., Fuß, R., Helfrich, M., Flessa, H., Well, R., 2016.
Fluxes of N2 and N2O and contributing processes in summer after grassland renewal and
grassland conversion to maize cropping on a Plaggic Anthrosol and a Histic Gleysol. Soil
Biology and Biochemistry 101, 6-19. |
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