Journal article
Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils
Ecosystems, Biosystems Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark1
Biosystems Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark2
Risø National Laboratory for Sustainable Energy, Technical University of Denmark3
Natural N-15 abundance measurements of ecosystem nitrogen (N) pools and N-15 pool dilution assays of gross N transformation rates were applied to investigate the potential of delta N-15 signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria.
Soil delta N-15 values of both forest sites increased with depth to 50 cm, but then decreased below this zone. delta N-15 values of microbial biomass (mixed stand: 4.7 +/- 0.8 parts per thousand, spruce stand: 5.9 +/- 0.9 parts per thousand) and of dissolved organic N (DON; mixed stand: 5.3 +/- 1.7 parts per thousand, spruce stand: 2.6 +/- 3.3 parts per thousand) were not significantly different; these pools were most enriched in N-15 of all soil N pools.
Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant N-15 enrichment of its substrate NO3- (3.6 +/- 4.5 parts per thousand) compared to NH4+ (-4.6 +/- 2.6 parts per thousand) and its product N2O (-11.8 +/- 3.2 parts per thousand). In a N-15-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification.
Moreover, in natural abundance measurements the NH4- pool was slightly N-15-enriched (-0.4 +/- 2.0 parts per thousand) compared to NO3- (-3.0 +/- 0.6 parts per thousand) and N2O (-2.1 +/- 1.1 parts per thousand) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O.
The more positive delta N-15 values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural N-15 abundance and N-15 tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.
Language: | English |
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Publisher: | Kluwer Academic Publishers |
Year: | 2007 |
Pages: | 79-94 |
Journal subtitle: | An International Journal on Plant-soil Relationships |
ISSN: | 15735036 and 0032079x |
Types: | Journal article |
DOI: | 10.1007/s11104-007-9264-y |