Elucidating molecular level impact of peat fire on soil organic matter by laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry
In this work, laser desorption ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (LDI–FTICRMS) was used to investigate the molecular composition of a peat fire and laboratory heated soil organic matter (SOM). SOM isolated from soils obtained from unburned and burned sites at Central Kalimantan, Indonesia, were analyzed with LDI–FTICRMS. About 7500 peaks were found and assigned with molecular formulas for each mass spectrum. SOM isolated from fire-affected soil sites are relatively more abundant in low oxygenated classes (e.g., O1–O5) and thermally stable compounds, including condensed hydrocarbon and nitrogen heterocyclic compounds. Abundances of highly condensed hydrocarbon compounds with carbon number > 30 were increased for the fire-affected SOM. In vivo heating experiments were conducted for SOM extracted from unburned sites, and the prepared SOMs were analyzed with LDI–FTICRMS. Overall, the same trend of change at the molecular level was observed from both the laboratory heated and the peat fire-affected SOM samples. In addition, it was observed that heat caused the degradation of SOM, generating lignin and tannin-type molecules. It was hypothesized that they were formed by thermal degradation of high molecular weight SOM. All the information presented in this study was obtained by consuming ~ 5 μg of sample. Therefore, this study shows that LDI–FTICRMS is a sensitive analytical technique that is effective in obtaining molecular level information of SOM.
KeywordsLDI–FTICRMS Molecular transformation Peat fire Soil organic matter
We acknowledge the support for this work from the National Research Foundation of Korea (NRF) grant, funded by the Korea Government (MSIP) grant no. 2017R1A2B3003455, and the National Strategic Project-Fine Particle of the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (MSIT), the Ministry of Environment (ME), and the Ministry of Health and Welfare (MOHW) (2017M3D8A1090658).
The manuscript was written through contributions of all authors.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
For the use of Sebangau National Park soil in this study, permission was received from Sebangau National Park through Palangka Raya University, Hokkaido University, and Indonesian Institute of Sciences (LIPI) in a collaborative research project entitled “Wildfire and Carbon Management in Peat-forest in Indonesia, 2008–2014” funded by JST-JICA.
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