Characterization of Sequentially Extracted Soil Organic Matter by Electrospray Ionization and Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Persistent URL
Author(s)
Wang, Yinghui
Liu, Yina
Chu, Rosalie K.
Bowden, Richard D. (Rich)
Lajtha, Kate
Simpson, Myrna J.
Wang, Junjian
Date Issued
September 15, 2022
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.
Journal
ACS Earth and Space Chemistry
Department
Environmental Science / Studies
Citation
ACS Earth Space Chem. 2022, 6, 9, 2142–2148
Publisher
American Chemical Society
Version of Article
Final manuscript post peer review, without publisher's formatting or copy
editing (postprint)
DOI
10.1021/acsearthspacechem.2c00180
ISSN
2472-3452