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| Titel |
Two-dimensional NMR spectroscopy links structural moieties of soil organic matter to the temperature sensitivity of its decomposition |
| VerfasserIn |
Laure Soucemarianadin, Björn Erhagen, Mats Öquist, Mats Nilsson, Jurgen Schleucher |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103955
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| Publikation (Nr.) |
 EGU/EGU2015-3379.pdf |
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| Zusammenfassung |
| Soil organic matter (SOM) represents a huge carbon pool, specifically in boreal ecosystems.
Warming-induced release of large amounts of CO2 from the soil carbon pool might become a
significant exacerbating feedback to global warming, if decomposition rates of boreal soils
were more sensitive to increased temperatures. Despite a large number of studies dedicated to
the topic, it has proven difficult to elucidate how the organo-chemical composition
of SOM influences its decomposition, or its quality as a substrate for microbial
metabolism. A great part of this challenge results from our inability to achieve a detailed
characterization of the complex composition of SOM on the level of molecular structural
moieties.
13C nuclear magnetic resonance (NMR) spectroscopy is a common tool to characterize
SOM. However, SOM is a very complex mixture and the chemical shift regions distinguished
in the 13C NMR spectra often represent many different molecular fragments. For example, in
the carbohydrates region, signals of all monosaccharides present in many different polymers
overlap. This overlap thwarts attempts to identify molecular moieties, resulting in insufficient
information to characterize SOM composition.
We applied two-dimensional (2D) NMR to characterize SOM with highly increased
resolution. We directly dissolved finely ground litters and forest floors—fibric and humic
horizons—of both coniferous and deciduous boreal forests in dimethyl sulfoxide and
analyzed the resulting solution with a 2D 1H-13C NMR experiment. In the 2D planes of these
spectra, signals of CH groups can be resolved based on their 13C and 1H chemical shifts,
hence the resolving power and information content of these NMR spectra is hugely
increased. The 2D spectra indeed resolved overlaps observed in 1D 13C spectra,
so that hundreds of distinct CH groups could be observed and many molecular
fragments could be identified. For instance, in the aromatics region, signals from
individual lignin units could be recognized. It was hence possible to follow the
fate of specific structural moieties in soils. We observed differences between litter
and soil samples, and were able to relate them to the decomposition of identifiable
moieties.
Using multivariate data analysis, we aimed at linking the detailed chemical fingerprints of
SOM to turnover rates in a soil incubation experiment. With the multivariate models, we were
able to relate signal patterns in the 2D spectra and intensities of identifiable molecular
moieties to variability in the temperature response of organic matter decomposition, as
assessed by Q10.
In conclusion, the characterization of SOM composition at the molecular level by
solution-state 2D NMR spectroscopy is highly promising; it offers unprecedented
possibilities to link SOM molecular composition to ecosystem processes, and their responses
to environmental changes. |
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