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| Titel |
NMR spectroscopic study of the carbon and nitrogen dynamics of grass-derived pyrogenic organic material during 2.3 years of incubation in soil |
| VerfasserIn |
André Hilscher, Heike Knicker |
| 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 |
250044754
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| Zusammenfassung |
| Incomplete combustion of vegetation results in pyrogenic organic material (PyOM) which
occurs ubiquitously in soils and sediments. To understand the C sequestration potential of
PyOM in environmental systems knowledge is required about the respective degradation
and humification mechanisms and the stability of the different chemical PyOM
structures. The present study focuses on the microbial recalcitrance of PyOM on
molecular scale. Therefore, microcosms incubation experiments were performed
using PyOM produced from highly isotopically enriched 13C and 15N rye grass
(Lolium perenne) at 350-C under oxic conditions for one (1M) and four minutes
(4M). Solid-state CPMAS 13C and 15N NMR studies were accomplished to obtain
insights into the involved humification mechanisms at different stages the PyOM
degradation.
In total up to 38% of the bulk PyOM C was mineralised during the 28 months of incubation.
The O/N-alkyl C and alkyl C residues which survived the charring process were effectively
decomposed. At the end of the incubation up to 73% and 57% of the initial O/N-alkyl C and
alkyl C amount were mineralised or converted to other C groups, respectively. The total aryl
C group recovery of the PyOM decreased significantly during the 28 months of incubation (P
-¤ 0.001). After 20 months of incubation between 26% and 40% of the initial aryl C
amount was lost. For this group, relative short half time periods in the range of 3.0
and 3.8 years were obtained. The observed loss of aromatic C structures may be
attributed to two simultaneous processes, the mineralisation to CO2 and the conversion
to other C groups by partial oxidation. The presence of a readily decomposable
co-substrate showed no significant changes in the degradation pattern of the different
PyOM, possibly because decomposable sources were already available in the starting
PyOM.
Most of the organic bound N of the fresh PyOM was assignable to heterocyclic aromatic
compounds such as pyrrole and indole-like structures with contributions of 62% and 72% for
PyOM 1M and PyOM 4M, respectively. The other part of the 15N NMR signal
intensity was assignable to amide-like structures. No major alteration of the amide and
heterocyclic N contribution was detected for the PyOM 1M incubates. For the more
charred PyOM 4M, the relative heterocyclic N contribution decreased. After the
28 months of incubation no significant difference in the chemical N composition
of PyOM 4M related to the PyOM 1M treatments could be observed (P=0.472).
Further, we detect a continuous degrease of the total amounts for the amide and
heterocyclic N compounds. After 20 months, only 49% to 59% of the heterocyclic N
compounds were recovered. The respective amide N recoveries were larger with 59% to
87%.
It can be concluded, that PyOM may not be as highly refractory as it is commonly assumed.
During the efficient degradation not only a considerable PyOM amount is mineralised, but
also the chemical structure of the remaining PyOM is strongly modified. This includes the
formation of O-containing functional groups and the loss of aromatic C and N containing
heterocyclic domains by mineralisation and conversion to other C and N groups. |
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