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Explaining the doubling of N 2 O emissions under elevated CO 2 in the Giessen FACE via in-field 15 N tracing.
- Source :
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Global change biology [Glob Chang Biol] 2018 Sep; Vol. 24 (9), pp. 3897-3910. Date of Electronic Publication: 2018 Apr 16. - Publication Year :
- 2018
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Abstract
- Rising atmospheric CO <subscript>2</subscript> concentrations are expected to increase nitrous oxide (N <subscript>2</subscript> O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N <subscript>2</subscript> O emission increases under elevated atmospheric CO <subscript>2</subscript> (eCO <subscript>2</subscript> ), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO <subscript>2</subscript> Enrichment (GiFACE): a permanent grassland that has been exposed to eCO <subscript>2</subscript> , +20% relative to ambient concentrations (aCO <subscript>2</subscript> ), for 15 years. We applied in the field an ammonium-nitrate fertilizer solution, in which either ammonium ( NH 4 + ) or nitrate ( NO 3 - ) was labelled with <superscript>15</superscript> N. The simultaneous gross N transformation rates were analysed with a <superscript>15</superscript> N tracing model and a solver method. The results confirmed that after 15 years of eCO <subscript>2</subscript> the N <subscript>2</subscript> O emissions under eCO <subscript>2</subscript> were still more than twofold higher than under aCO <subscript>2</subscript> . The tracing model results indicated that plant uptake of NH 4 + did not differ between treatments, but uptake of NO 3 - was significantly reduced under eCO <subscript>2</subscript> . However, the NH 4 + and NO 3 - availability increased slightly under eCO <subscript>2</subscript> . The N <subscript>2</subscript> O isotopic signature indicated that under eCO <subscript>2</subscript> the sources of the additional emissions, 8,407 μg N <subscript>2</subscript> O-N/m <superscript>2</superscript> during the first 58 days after labelling, were associated with NO 3 - reduction (+2.0%), NH 4 + oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO <subscript>2</subscript> provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N <subscript>2</subscript> O:N <subscript>2</subscript> emission ratio, explains the doubling of N <subscript>2</subscript> O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change.<br /> (© 2018 John Wiley & Sons Ltd.)
Details
- Language :
- English
- ISSN :
- 1365-2486
- Volume :
- 24
- Issue :
- 9
- Database :
- MEDLINE
- Journal :
- Global change biology
- Publication Type :
- Academic Journal
- Accession number :
- 29569802
- Full Text :
- https://doi.org/10.1111/gcb.14136