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| Titel |
Dynamics of nitrate limitation on gaseous nitrogen exchanges from pristine peatlands |
| VerfasserIn |
D. Roobroeck, N. Brüggemann, K. Butterbach-Bahl, P. Boeckx |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030097
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| Zusammenfassung |
| The cycling of gaseous nitrogen species in peatland ecosystems and the functioning of
driving forces on microbial denitrification rates are poorly accounted. Physico-chemical soil
conditions and biotic interactions1 control the availability of nitrate for respiratory
denitrification resulting in high spatial variability of gaseous nitrogen exchange rates in
nutrient poor peat soils and complicating impact assessment of eutrophication. The responses
of nitrous oxide (N2O) and dinitrogen (N2) fluxes to nitrate addition were compared between
distinct contrasts in plant growth at a pristine, hummocky peatland. Allowing to determine
the dynamics of nitrate limitation on gaseous nitrogen exchanges in accordance to covariance
in soil anaerobiosis and resource competition.
Two quantification techniques were applied parallel to soil core incubations in order to
determine N2O and N2 fluxes. Helium atmosphere incubation was used for direct
quantification of net N2O and N2 fluxes. Reducing the background N2 concentration in the
soil atmosphere to approx. 20 ppm enabled highly sensitive measurement of N2 fluxes. On
the other hand a 15N-N2O tracer technique was explored as a tool to demonstrate and
quantify gross consumption rates of atmospheric N2O to N2 and recycling of gaseous
N-losses by microbial fixation. The headspace N2O pool was increased with 0.03 ppm
15-15N-N2O rendering an enrichment of ± 9.8 atom% 15-15N-N2O. Triplicate soil core
samples were taken from two contrasting soil habitat in a hummocky, Carex dominated fen
located in the Biebrza National Park, NE Poland (53-07-²N; 23-10-²E). The hummocks had a
gravimetric soil water content of 76.6 ± 2.2% and high root abundance, dissimilar to
83.4 ± 1.0% and little root prevalence in the hollows. Singular nitrate addition,
comparable to the atmospheric NOY -deposition, was applied two days in advance of flux
measurement.
Actual net gaseous nitrogen fluxes and responses to nitrate addition were apparently different
for both soil habitat. Hummock soil cores showed to be net sources of N2O sinks (-3.04 ±
0.12 μg N2O-N h-1 m-2). Net N2 fluxes measured consistently higher from the hollows than
the hummocks (resp. 2622.3 ± 106.3 and 1065.3 ± 139.2 μg N2-N h-1 m-2). Nitrate
addition to the hummock habitat resulted in a small, non-significant increase of the net N2O
flux, while the hollow soil cores showed a drastic shift towards a net N2O source upon nitrate
addition (16.27 ± 2.87 μg N2O-N h-1 m-2). The N2:N2O ratios and net N2O fluxes clearly
illustrated that relatively more bio-available nitrogen is converted to N2O by respiratory
denitrification at higher soil nitrate availability. The 15-15N-N2O tracer technique
demonstrated consumptive reduction of atmospheric N2O to N2. With NO3–addition the
atom percent excess of 15N in N2 decreased for both soil habitat indicating that less
atmospheric N2O is reduced to inert N2 when more nitrate is available for microbial
denitrification. N2O consumption rates will be discussed on the presentation. Indirect
fumigation of soil samples proved that CHCl3-labile nitrogen was significantly
enriched in 15N when 15N-N2O was applied in the headspace. Demonstrating that
nitrogen lost during respiratory denitrification is recycled to microbial biomass, most
likely a result of N2-fixation by soil micro-organisms in this mineral N-depleted
ecosystem.
Higher root abundance associated with lower soil anaerobiosis and higher resource
competition caused net N2O fluxes to be positive, but mitigated the effect of nitrate addition.
Lower root abundance associated with higher soil anaerobiosis, caused natural peat soil to be
net N2O sinks, but lower resource competition however attributed to higher eutrophication
susceptibility. Variance in physico-chemical soil conditions and biotic interactions showed to
interfere with the effect of nitrate availability on consumptive reduction of atmospheric N2O
to N2. Inverse covariance of soil anaerobiosis and resource competition as a result of variance
in plant growth indicated to be a major regulatory dynamic of gaseous nitrogen
exchanges from natural peatland, by which the susceptibility to nitrate eutrophication is
determined.
References
1 Silvan, N., Tuittila, E., Kitunnen, V., Vasander, H., Laine, J., 2005. Nitrate uptake by
Eriophorum vaginatum controls N2O production in a restored peatland, Soil Biology &
Biochemistry, 37:1519-1526. |
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