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| Titel |
Microhabitat Effects on N2O Emissions from Floodplain Soils under Controlled Conditions |
| VerfasserIn |
Martin Ley, Moritz F. Lehmann, Pascal A. Niklaus, Thomas Kühn, Jörg Luster |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132814
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| Publikation (Nr.) |
 EGU/EGU2016-13355.pdf |
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| Zusammenfassung |
| Semi-terrestrial soils such as floodplain soils are considered to be potential hotspots of nitrous
oxide (N2O) emissions. The quantitative assessment of N2O release from these hotspots
under field conditions, and of the microbial pathways that underlie net N2O production
(ammonium oxidation, nitrifier-denitrification, and denitrification) is challenging because of
their high spatial and temporal variability. The production and consumption of N2O
appears to be linked to the presence or absence of micro-niches, providing specific
conditions that may be favorable to either of the relevant microbial pathways. Flood
events have been shown to trigger moments of enhanced N2O emission through a
close coupling of niches with high and low oxygen availabilities. This coupling
might be modulated by microhabitat effects related to soil aggregate formation, root
soil interactions and the degradation of organic matter accumulations. In order to
assess how these factors can modulate N2O production and consumption under
simulated flooding/drying conditions, we have set up a mesocosm experiment with
N-rich floodplain soils comprising different combinations of soil aggregate size
classes and inert matrix material. These model soils were either planted with basket
willow (Salix viminalis L.), mixed with leaf litter, or left untreated. Throughout a
simulated flood event, we repeatedly measured the net N2O production rate. In addition,
soil water content, redox potential, as well as C and N substrate availability were
monitored. In order to gain insight into the sources of, and biogeochemical controls
on N2O production, we also measured the bulk δ15N signature of the produced
N2O, as well as its intramolecular 15N site preference (SP). In this presentation
we focus on a period of enhanced N2O emission during the drying phase after 48
hrs of flooding. We will discuss the observed emission patterns in the context of
possible treatment effects. Soils with large aggregates showed a tendency to emit
more N2O than small-aggregate soils. Salix viminalis strongly suppressed the N2O
emissions, fully compensating for any aggregate effects. Litter accumulation on
the other hand enhanced N2O emission from well-aggregated soils, but showed
only a small effect in combination with small aggregates. In moments of highest
emission rates, the measured δ15Nbulk of headspace N2O was considerably lower
relative to atmospheric N2O (δ15N between -20 ‰ and -25 ‰ ) in the amended
treatments, suggesting N2O production by denitrification or by nitrifier-denitrification.
Untreated mesocosms produced an even lower δ15Nbulk (-40‰ ). Similarly, aggregate
formation/size seemed to affect the N2O δ15Nbulk values, suggesting different net
N2O production dynamics under different microhabitat conditions, which will be
elucidated further, using 15N site preference SP data. Combining stable isotope
techniques with quantitative flux data from a mesoscale laboratory experiment, our
data highlight the importance of microhabitat effects in modulating N2O emission
from floodplain soils. It also underscores their influence on the N2O production
pathways involved in the occurrence of N2O emission hot spots and moments. |
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