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| Titel |
Two-dimensional NMR spectroscopy as a tool to link soil organic matter composition to ecosystem processes |
| VerfasserIn |
Laure Soucemarianadin, Björn Erhagen, Mats Öquist, Mats Nilsson, Jurgen Schleucher |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097197
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| Publikation (Nr.) |
 EGU/EGU2014-12749.pdf |
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| Zusammenfassung |
| Environmental factors (e.g. temperature and moisture) and the size and composition of soil
microbial populations are often considered the main drivers of soil organic matter (SOM)
mineralization. Less consideration is given to the role of SOM as a substrate for microbial
metabolism and the importance of the organo-chemical composition of SOM on
decomposition. In addition, a fraction of the SOM is often considered as recalcitrant to
mineralization leading to accumulation of SOM. However, recently the concept of
intrinsic recalcitrance of SOM to mineralization has been questioned. The challenge in
investigating the role of SOM composition on its mineralization to a large extent stems
from the difficulties in obtaining high resolution characterization of a very complex
matrix.
13C nuclear magnetic resonance (NMR) spectroscopy is a widely used tool to
characterize SOM. However, SOM is a very complex mixture and in the resulting 13C
NMR spectra, the identified functional groups may represent different molecular
fragments that appear in the same spectral region leading to broad peaks. These overlaps
defy attempts to identify molecular moieties, and this makes it impossible to derive
information at a resolution needed for evaluating e.g. recalcitrance of SOM. Here we
applied a method, developed in wood science for the pulp paper industry, to achieve a
better characterization of SOM. We directly dissolved finely ground organic layers
of boreal forest floors—litters, fibric and humic horizons of both coniferous and
broadleaved stands—in dimethyl sulfoxide and analyzed the resulting solution with a
two-dimensional (2D) 1H-13C NMR experiment. We will discuss methodological
aspects related to the ability to identify and quantify individual molecular moieties in
SOM. We will demonstrate how the spectra resolve signals of CH groups in a 2D
plane determined by the 13C and 1H chemical shifts, thereby vastly increasing
the resolving power and information content of NMR spectra. The obtained 2D
spectra resolve overlaps observed in 1D 13C spectra, so that hundreds of distinct
CH moieties can be observed and many individual molecular fragments can be
identified. For instance, in the aromatic spectral region, signals originating from
various lignin monomers and unsaturated compounds can be resolved. This yields a
detailed chemical fingerprint of the SOM samples, and valuable insights on molecular
structures.
We observed differences in the respective aromatic region of the 2D spectra of
the litter layers and the fibric and humic horizons, in relation with humification
processes. We were also able to relate the cross-peak complexity and abundance
patterns of identifiable molecular moieties to variability in the temperature response of
organic matter degradation, as assessed by Q10. To conclude, solution-state 2D NMR
spectroscopy is a highly promising new tool to characterize SOM composition at the
molecular level, which opens completely new possibilities to link SOM molecular
composition to ecosystem processes, and their responses to environmental changes. |
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