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| Titel |
Denitrification kinetics support high nitrous oxide emissions in West Siberian cryoturbated tundra |
| VerfasserIn |
Hanna Silvennoinen, Annelene Pengerud, Christina Biasi, Peter Dörsch |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051616
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| Zusammenfassung |
| High N2O emissions have been reported from West Siberian cryoturbated tundra soil, so
called peat circles (Repo et al. 2009). However, the processes behind the high N2O
emissions are not known. We studied denitrification kinetics, N2O production rates
and carbon mineralization in soil from both the cryoturbated peat circle without
vegetation and the surrounding non-turbated peat with vegetation (0-5 and 15-20 cm
depth, 3 field replicates each). Peat circle soil was visually more decomposed, had
higher nitrate contents but similar low pH (3.1) as compared with non-turbated
peat.
When incubated anaerobically as loose soil, the cryoturbated peat produced much higher
amounts of N2O than the non-turbated peat. In addition, the N2O product ratio for
denitrification (as inferred from incubation with and without 10 vol% acetylene) was much
higher in cryoturbated than in non-turbated peat, suggesting that instantaneous nitrous
oxide reductase (N2OR) activity in cryoturbated soil is absent or low. Significant
N2 production in cryo-turbated soil occurred only after all nitrate was consumed,
illustrating that the peat circle denitrifier community can express N2OR. Albeit at
much lower rates, the non-turbated soils showed a more balanced denitrification
upon oxic-anoxic transition characterized by instantaneous N2 production with
little N2O accumulation. Unbalanced denitrification in peat circle soil was also
indicated by μmolar NO accumulation whereas no measurable NO production was
found in the non-turbated soil. Contrasts in denitrification performance persisted
when incubating the soils as anoxic soil slurries and adding nitrate and glucose to
the non-turbated soil to equalize substrate concentrations. Together, our findings
suggest that the active denitrifying communities in the two soils represent distinct
denitrification phenotypes; active denitrifiers in the N-abundant cryoturbated soil
appear to be more sloppy in regulating electron flow resulting in higher N loss
in form of NO and N2O. The non-turbated denitrifying community, in contrast,
tightly regulates electron flow to N-oxides, which probably reflects the scarcity
of N-oxides in tundra soil. Molecular studies are on its way to clarify taxonomic
denitrifier composition in cryoturbated and non-turbated tundra soil (Palmer, K. et
al.).
To test the hypothesis that higher denitrification rates in cryoturbated peat are due to
accelerated in situ mineralization, we also studied CO2 production in a long-term incubation
experiment with fresh loose soil (90d, 15 Ë C). The cryoturbated soil exhibited much lower C
mineralization rates than the top soil of the non-turbated tundra, most probably reflecting the
absence of fresh organic carbon in this vegetation-free soil. Nevertheless, the low CO2
production in the peat circles is in contrast to the high denitrification rates and illustrates a
decoupling of C and N cycling in long-term turbated arctic soil. Apparently, the
gradual decline of the C/N ratio in cryo-turbated soil (Repo et al. 2009) has fostered a
viable denitrifier community through increasing net release of mineral nitrogen.
Carbon limitation together with abundant N-oxide availability, in turn, may be one
reason for the observed low instantaneous N2O reductase activity in the peat circle
soil.
References: Repo M, Susiluoto S, Lind SE, Jokinen S, Elsakov V, Biasi C, Virtanen T,
Martikainen PJ. 2009. Large N2O emissions from cryoturbated peat soil in tundra. Nature
Geoscience 2: 189-192. |
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