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| Titel |
High N2O emission in an N-saturated subtropical forest, southwest China |
| VerfasserIn |
P. Dörsch, J. Zhu, J. Mulder |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068204
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| Zusammenfassung |
| Nitrogen (N)-saturated forests in subtropical China are significant N sinks, despite low forest
growth rates. In a forested headwater catchment at Tieshanping, Chongqing, SW China, with
4 g N m-2a-1 atmogenic deposition (60% of which as NH4+-N) and leaching of only 0.6 g
N m-2 a-1 (NO3--N dominated), we applied state-of-the-art field and laboratory
methodologies to investigate the nature of the N sinks. The study included the determination
of spatiotemporal patterns of N2O emission, a 15N labeling experiment and laboratory
incubations to determine nitrification and denitrification characteristics and their gaseous
product stoichiometries.
Emission of N2O occurred predominantly during the wet season (summer), driven by rain
episodes. N2O emission rates were particularly high along a hill slope (HS) with a thin
organic surface layer overlaying an argic B horizon causing transient interflow during
storm flow conditions. Lower N2O emission rates were observed at the foot slope in
a colluvium-derived groundwater discharge zone (GDZ). Laboratory incubation
experiments suggested that the difference in N2O emission rate is primarily due to
higher N2O/N2 product ratios of denitrification in the HS topsoil being exposed
to frequent drying-rewetting. Lower N2O/N2 product ratios in soils of the GDZ,
in turn, could be attributed to more stable anoxia, lower NO3- availability and
higher pH as compared with the hillslope, all of which favor the expression of N2O
reductase.
Estimated annual N2O emission for the relatively dry hydrological year 2009-2010 was
0.4 g N m-2, which is equivalent to approximately 10% of the annual input of reactive N.
Measurements during summer 2009 indicated that N2O emissions can be even higher during
wet years. A 15NO3- labeling experiment conducted on HS soils during summer revealed
that between 75 and 86% of the N2O emission derived from denitrification during the first 6
days after label addition, accounting for 8-15% of the applied NO3--N. Our study indicates
that N-saturated subtropical forests in south China, receiving large inputs of agriculturally
derived atmogenic NH4+, may be significant secondary sources of N2O, which should be
taken into account when estimating the CO2 footprint of subtropical agriculture. |
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