The Molecular Composition of Humic Substances Isolated From Yedoma Permafrost and Alas Cores in the Eastern Siberian Arctic as Measured by Ultrahigh Resolution Mass Spectrometry

Abstract

Ongoing climate change is making the large pool of organic matter (OM) stored in Arctic permafrost vulnerable to mobilization; thus, garnering a deeper understanding of molecular transformations within the abundant pool of soil OM, specifically humic substances, is crucial. Here we present the first high-resolution mass-spectrometry examination of molecular compositions of humic acid (HA) and fulvic acid (FA) isolated from organic-rich deep yedoma (Pleistocene age ice-rich permafrost) and alas (thermokarst deposit formed during permafrost thaw) cores. The FA fractions were dominated by oxygen-rich unsaturated compounds, whereas the HA fractions were mostly composed of relatively reduced saturated and aromatic moieties. A substantial increase in contribution of both CHO-only and N-containing aliphatic compounds was observed in the HA fractions of the yedoma OM with depth, whereas the alas HA fractions were depleted in aliphatics but enriched with condensed and hydrolyzable tannins. The observed differences in compositional space of the immobile OM stored in the deep yedoma versus alas deposits were consistent with evolution of OM during thermokarst lake genesis, implying intense microbial degradation of N-rich OM released from the yedoma deposits and accumulation of highly degraded, plant-derived OM. The patterns of molecular transformations of OM were apparent in compositional space of the least degraded HA fractions as compared to much more oxidized FA fractions. This shows great promise of molecular exploration of the alkali-extracted OM, comprising up to 50% of the total organic carbon in deep permafrost both for paleoreconstructions and predictions of climate feedback to released OM due to permafrost thaw.

Bioactivity of Humic Acids Extracted From Shale Ore: Molecular Characterization and Structure-Activity Relationship With Tomato Plant Yield Under Nutritional Stress

“…To date, extended literature has been produced on the application of FT-ICR MS to NOM and its fractions, mostly in relation to dissolved organic matter (DOM) (Brown and Rice, 2000;Kujawinski, 2002;Stenson et al, 2002;Sleighter and Hatcher, 2007;Remucal et al, 2012;Lv et al, 2016). But, when it comes to the terrestrial soil organic matter (SOM) and its fractions, only a few publications arise (Kramer et al, 2004;Ohno et al, 2010;Piccolo et al, 2010;Ohno and Ohno, 2013;Zherebker et al, 2019), whereas investigations on other sources such as ores or compost are rare. A recent innovative approach has been incorporated in the pipeline of the studies on biologically active metabolites, where molecular formulas obtained by FT-ICR MS were sourced from public online databases with valuable results that helped gathering insights into the chemistry of HS (Fedoros et al, 2018;Orlov et al, 2019;Zhernov et al, 2020).…”

Refinement of Compound Aromaticity in Complex Organic Mixtures by Stable Isotope Label Assisted Ultrahigh-Resolution Mass Spectrometry

“…Hence, AI is the most conservative aromatic system approximation. Despite known limitations of these indices (especially AI mod ), they currently serve as major structural parameters in many geochemical studies of NOM/HS. − The use of AI may thus lead to false conclusions about the aromatic character of molecules for structurally constrained samples. For example, we have recently shown that molecules with the same low AI value (e.g., 0.3) may correspond to isomers with and without aromatic rings depending on the geochemical origin …”

Natural complex mixtures unequivocally defined in formulae difference space

“…However, the formulae list detected for coal HA (CHA-h 36 ) was not unequivocally assigned to the CHA sample from the database: based on top-ranked 9000 FDs, SHA-Ctk suggested the lowest FDCEL distance, but CHA would be a second choice. The unconventional result was also obtained for FA samples, which were isolated from the permafrost soil 37 . Supposedly, FA1-Y-15 and FA2-Y-15 are represented by the low-transformed organic compounds well conserved under the ice shield.…”

“…Dataset I includes formulae lists acquired for SRFA with various ionization techniques: ESI (SRFA-r 24 , SRFA-t 11 , SRFA-u 25 ), LDI (SRFA-s 26 ), PSI (SRFA-v 25 ), PSCI (SRFA-w 25 ). Dataset G for geochemical application verification includes various formulae lists: SLNOM-XAD, SLNOM-PPL 27 ; PRNOM, AHF-RPP-10, AHF-RPP-11, AHF-RK5P-10, AHF-RK6P-10, AHF-AOP-10 31 ; SDOM-GF 33 ; PHA-TTL 35 ; coal humic acid CHA-h has been described elsewhere 36 and it has been analyzed via Bruker Daltonics 12 Tesla Apex Qe FTICR-MS, housed at the College of Sciences Major Instrumentation Cluster (COSMIC) at Old Dominion University; FA1-Y-15, FA2-Y-15 37 .…”