Characterization of Sequentially Extracted Soil Organic Matter by Electrospray Ionization and Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Project Author
Issue Date
2022-09-15
Authors
Wang, Yinghui
Liu, Yina
Chu, Rosalie K.
Bowden, Richard D. (Rich)
Lajtha, Kate
Simpson, Myrna J.
Wang, Junjian
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Keywords
Fourier transform ion cyclotron resonance mass spectrometry , Ionization selectivity , Soil organic carbon , Nitrogen deposition , Sequential extraction
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Abstract
Soil organic matter (SOM) is a complex mixture of small molecules and biopolymers that are active in various biogeochemical processes. However, the chemical diversity of biopolymer-derived SOM remains poorly explored. Identifying this diversity is important because global environmental changes may well alter SOM chemistry, as field experiments are beginning to show. Here, organic solvent-extractable (DcM(e)-SOM), base-hydrolyzable (KOHHy-SOM), and CuO-oxidizable (CuOOx-SOM) SOM fractions from a forest with a long-term nitrogen addition experiment were sequentially extracted and characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with negative-ion electrospray ionization (ESI) or atmospheric pressure photoionization (APPI). From DcMe-SOM to CuOOx-SOM, the total number of assigned formulas, average O/C ratio, aromaticity, and unsaturation degree of SOM continuously increased, while the average m/z and H/C ratio decreased. Moreover, the dominant chemical category shifted from lipid-like components to phytochemical-and protein-like components. Complementary to ESI, APPI effectively facilitated detection of additional compounds with low polarity. With long-term nitrogen addition, the average m/z, unsaturation degree, aromaticity, and oxidation state of SOM increased, and more aromatic nitrogen-containing formulas were detected in CuOOx-SOM. Our study demonstrates that chronic nitrogen deposition in forests alters both the small molecules and biopolymers of SOM fundamentally.
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Major
Department
Environmental Science / Studies
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Citation
ACS Earth Space Chem. 2022, 6, 9, 2142–2148
Version
Final manuscript post peer review, without publisher's formatting or copy
editing (postprint)
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Publisher
American Chemical Society