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| Titel |
Quantification of transformation rates of soil amino sugars and amino acids by a novel isotope pool dilution approach via liquid chromatography/high resolution mass spectrometry (LC/HRMS) |
| VerfasserIn |
Yuntao Hu, Qing Zheng, Lisa Noll, Shasha Zhang, Wolfgang Wanek |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143879
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| Publikation (Nr.) |
 EGU/EGU2017-7643.pdf |
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| Zusammenfassung |
| Organic nitrogen transformation processes are the key driver of soil nitrogen availability,
strongly affecting the nitrogen turnover and carbon cycling of terrestrial ecosystems.
Low molecular weight organic nitrogen compounds (e.g. amino acids and amino
sugars) that can be directly utilized by plants or microorganisms are released by the
extracellular cleavage of high molecular weight organic nitrogen compounds (e.g. proteins,
peptidoglycan, and chitin) by hydrolytic enzymes. This decomposition process is believed to
be the rate-limiting step in the soil N cycle. Direct measurements of the in situ
transformation rates of these small N compounds is highly challenging but can
be realized by applying the isotope pool dilution (IPD) technique, in which the
target compound pool is labeled with isotopic tracers and subsequently the dilution
of the tracers is measured. We have recently pioneered the development of IPD
assays to investigate the in situ flux of proteinaceous amino acids and glucose due to
decomposition of organic matter and microbial utilization, but the roles of fluxes of amino
sugars and amino acid enantiomers in soil nitrogen transformation processes are still
unknown due to the lack of feasible extraction, purification, separation and detection
methods.
Here we developed a 15N IPD assay by utilizing a novel LC/HRMS (Orbitrap) platform,
with the aim to measure transformation rates of amino sugars and amino acid enantiomers.
After the tracer experiments soil extracts were purified by solid phase extraction prior to
the analysis by MS. The utilization of Orbitrap-HRMS allowed us to resolve the
mass signals of unlabeled analytes, and their 15N labeled (tracers) and 13C labeled
(internal standards) analogues. The commercially unavailable 15N and 13C labeled
amino sugars and amino acid enantiomers were produced from bacterial cell walls
after batch culture in labeled growth media. This workflow was validated with soils
from two sampling sites, allowing us to successfully investigate the production and
consumption of 2 amino sugars, 18 amino acids, and 4 amino acid enantiomers in
soils.
We further applied this method to soils from 6 sampling sites differing in geology
and land management, after short-term (1-day) temperature (5˚ C, 15˚ C, 25˚ C)
pre-incubations. We found that the release of amino sugars (free glucosamine) during the
decomposition of peptidoglycan and chitin accounted for approximately 5% to 15% of the
total influx into the dissolved organic nitrogen pool (amino acids plus amino sugars).
Muramic acid exhibited significantly longer residence times in soils, indicating that
free muramic acid was not an important decomposition product of peptidoglycan
in soil. We will present further results on potential controls of soil amino sugar
fluxes, such as soil temperature, geology and land management, as well as soil
peptidoglycan and chitin content, hydrolytic enzyme activity, and microbial community
structure. These findings and further ongoing work will greatly advance our knowledge
of the transformation processes of soil organic nitrogen and its major controls. |
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