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| Titel |
Does nitrogen deposition affect plant-derived and microbial organic matter compounds differently? |
| VerfasserIn |
Alexander Heim, Frank Hagedorn, Michael W. I. Schmidt |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040056
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| Zusammenfassung |
| The IPCC report 2007 assesses soil nitrogen availability as a key factor in predicting future
carbon sequestration by terrestrial ecosystems. However, various studies reported contrasting
N effects on SOM dynamics, but the reasons for this are not well understood. One potential
explanation is that decomposition processes of individual organic molecules respond
differently to nitrogen. Compound-specific stable isotope analysis (CSIA) of C
(and N) can be used to trace isotopically labeled molecules in soil. While such an
isotopic label can be relatively easily obtained in arable soils via crop changes
from C3 to C4 plants, this option does not exist for forests. Therefore, no data on
molecular dynamics of forest soils and their response to changes in environmental
conditions (increase in atmospheric CO2 concentrations and in N deposition) exist so
far.
Nonetheless, labeling of forest ecosystems is possible by fumigation with labeled CO2,
although only very few of these experiments are available worldwide.
In a new project, we will use archived soil samples from a CO2 enrichment experiment in
large open-top chambers. This experiment had been conducted in a factorial design to study
interactions between CO2 fumigation and N deposition on model forest ecosystems growing
on two contrasting soils. The analysis of 13C signatures in SOM fractions indicated a retarded
mineralization of old SOM in fine particle size fractions. In this study, we will apply
compound-specific isotope analysis to trace added CO2 into plant and microbial biomarkers
in soils. Thus, we will obtain systematic data on molecular dynamics in forest soils based on
a 13C labeling approach. In particular, we will test the hypothesis that decomposition of
N-containing compounds (such as microbial amino sugars) does not respond to N additions,
in contrast to decomposition of N-free compounds, such as lignin. The experimental
design also enables us to address potential interactive effects of CO2, N and soil
type on concentrations both of plant biomarkers and of microbial biomarkers. A
significant shift in the ratio between these biomarkers would be indicative of major
changes in the carbon fluxes within the soil system. Localization of the labeled
biomarkers in specific soil fractions will identify the soil compartments where important
changes occur. This information may be used to test current hypotheses on organic
matter stabilization mechanisms in soil. The project plan and first results will be
presented. |
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