title: Effect of ecosystem type and fire on chemistry of WEOM as measured by LDI-TOF-MS and NMR.
abstract: Soil organic matter (SOM) and its water-soluble components play an important role in terrestrial carbon cycling and associated ecosystem functions. Chemically, they are complex mixtures of organic compounds derived from decomposing plant material, microbial residues, as well as root exudates, and soil biota. To test the effect of the ecosystem type (forest and grassland) and fires events on the chemistry of dissolved organic matter (DOM), we applied a combination of laser-desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) and 2D (1H and13C) nuclear magnetic resonance (NMR) spectroscopy to water-extractable organic matter (WEOM) from a range of top soil samples. The aim was to assess the suitability of LDI-TOF-MS for the rapid characterization of WEOM. Therefore, we evaluated the effects of sample (pH and dilution) conditions and use of positive or negative reflector mode to identify the conditions under which LDI-TOF-MS best distinguished between WEOM from different sources. Thirty-six samples were measured with both analytical techniques and their chemical patterns were statistically evaluated to distinguish firstly the effect of the type of ecosystem (forest versus grassland) on WEOM characteristics, and secondly the impact of fire on the chemical composition of WEOM. The nonmetric multidimensional scaling (NMDS) analysis of the most suitable experimental LDI-TOF-MS conditions showed a clear separation between the type of vegetation and fire-induced changes, mostly reflecting the presence of poly(ethylene glycol) in grassland soils. Discrimination among WEOM from different vegetation types was preserved in the fire treated samples. The calculation of the relative abundance of certain functional structures in the WEOM samples revealed a common composition of forest and grassland WEOM, with polysaccharides and proteins making up to 60%. The compositional impact of forest fire on WEOM was more pronounced compared to the one of grassland, leading to a decline in the main components, and an increase in amino-sugars, fatty acids, and sterols. The recorded1H NMR and heteronuclear single quantum coherence (HSQC) spectra showed a decrease of the carbohydrate signal in WEOM from fire-treated samples, which was more pronounced in forest than in grassland soils.
authors.affiliation: Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany; Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany. Electronic address: anna.crecelius@uni-jena.de.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Crecelius
authors.affiliation: Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany; Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Vitz
authors.affiliation: Institute of Geography, Friedrich Schiller University Jena, Löbdergraben 32, 07743 Jena, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Näthe
authors.affiliation: Institute of Geography, Friedrich Schiller University Jena, Löbdergraben 32, 07743 Jena, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Meyer
authors.affiliation: Institute of Geography, Friedrich Schiller University Jena, Löbdergraben 32, 07743 Jena, Germany.
authors.forename: Beate
authors.initials: B
authors.lastname: Michalzik
authors.affiliation: Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany; Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany.
authors.forename: Ulrich S
authors.initials: US
authors.lastname: Schubert
keywords: (1)H nuclear magnetic resonance spectroscopy; (13)C nuclear magnetic resonance spectroscopy; Ecosystem type; Fire disturbance; Laser-desorption/ionization time-of-flight mass spectrometry; Nonmetric multidimensional scaling; Water-extractable organic matter