Application of pyrolysis‐field ionization mass spectrometry (Py‐FIMS) and synchrotron‐based X‐ray absorption spectroscopy (C‐ und N‐XANES) to determine heat effects on soil organic matter

Autor: Kiersch, Kristian; Zimmermann, Ralf; Kruse, Jens; Leinweber, Peter;
In:

Transfers and Transformations: Our Evolving Biosphere

Autor: Joint Conference of the Canadian Society of Soil Science & Canadian Society of Agronomy
Seite: 112 - 112
Jahr: 2010

Einordung:
Institut: Professur Bodenkunde

Abstract:
The organic carbon (C) and nitrogen (N) in soil form large pools of C and N on Earth’s surface and control soil fertility, plant productivity, biodiversity, C sequestration, and many other ecosystem services. Global warming caused more frequent and severe vegetation fires in parts of the world, and effects on bulk soil organic matter (SOM) were studied occasionally. Analytical methods with molecular resolution and quantification of such changes are unsatisfactory because of methodological limitations in the flash pyrolysis-gas chromatography coupled to mass spectrometry (MS), nuclear magnetic resonance spectroscopy, and thermal and chemical oxidation applied to this topic so far. Therefore, new methods are required to gain deeper insights into molecular-structural SOM changes arising from vegetation fire heat impact. The general objective of the research is to test and optimize methods for the determination of pyrolyzed organic matter (PyOM) in soils. As a first step we compared various MS and XANES methods to characterize SOM in samples from a long term field experiment in Germany, in which plots were periodically burned, mulched or left to natural succession. Results showed a larger sensitivity of temperature-resolved pyrolysis - field ionization MS (Py-FIMS) than for other MS and XANES methods in the detection of molecular differences among treatments. A principal component analysis of the Py-FIMS data separated the burned variants at two different locations from the others. The direct comparison of the variants showed a larger relative amount of m/z > 150 and a shift of thermal release of compounds to higher temperatures for the burned plots. Relative enrichments of heterocyclic N compounds in the N-XANES spectra of the burned plots can be explained by their heat-induced synthesis. Moreover, in a controlled burning experiment in the laboratory, the C- and N-XANES also showed characteristic formations of cyclic and heterocyclic molecules in SOM.

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