Indexing Permafrost Soil Organic Matter Degradation Using High-Resolution Mass Spectrometry

Abstract

Microbial degradation of soil organic matter (SOM) is a key process for terrestrial carbon cycling, although the molecular details of these transformations remain unclear. This study reports the application of ultrahigh resolution mass spectrometry to profile the molecular composition of SOM and its degradation during a simulated warming experiment. A soil sample, collected near Barrow, Alaska, USA, was subjected to a 40-day incubation under anoxic conditions and analyzed before and after the incubation to determine changes of SOM composition. A CHO index based on molecular C, H, and O data was utilized to codify SOM components according to their observed degradation potentials. Compounds with a CHO index score between –1 and 0 in a water-soluble fraction (WSF) demonstrated high degradation potential, with a highest shift of CHO index occurred in the N-containing group of compounds, while similar stoichiometries in a base-soluble fraction (BSF) did not. Additionally, compared with the classical H:C vs O:C van Krevelen diagram, CHO index allowed for direct visualization of the distribution of heteroatoms such as N in the identified SOM compounds. We demonstrate that CHO index is useful not only in characterizing arctic SOM at the molecular level but also enabling quantitative description of SOM degradation, thereby facilitating incorporation of the high resolution MS datasets to future mechanistic models of SOM degradation and prediction of greenhouse gas emissions.

Chemical composition of dissolved organic matter draining permafrost soils

“…Consistently, oxygen-poor, aliphatic compounds comprising the DOM pool in Siberian Arctic permafrost melt streams exhibited higher lability to biological degradation compared to less saturated, aromatic compounds within the permafrost DOM pool (Spencer et al, 2015). Thus, the abundance of relatively more labile oxygen-poor, aliphatic compounds may account for the observed increased bacterial growth efficiency or respiration of permafrost DOM once thawed and exported to surface waters (Mann et al, 2014;Abbott et al, 2014;Spencer et al, 2015;Mann et al, 2015; this study).…”

Valorization of Waste Wood as a Solid Fuel by Torrefaction

“…Thus, from Figures 3 and 4, the optimal torrefaction temperature for waste wood is 300 • C, with elevated GCV (MJ/kg), nominal mass loss, and less Ac (%). To describe the oxidation state of organic compound present in organic materials, Mann et al [24] suggested the use of the CHO index, defined as: Figure 5a shows the CHO index values of waste wood (current study) and for different lignocellulosic biomass obtained from [25], and Figure 5b denotes the CHO index obtained in this study with respect to torrefaction temperature. The higher the CHO index, the greater the number of oxygenated compounds.…”

Review of physicochemical properties and analytical characterization of lignocellulosic biomass

“…The equilibrium moisture contents have been determined for various biomass feedstocks, such as Miscanthus [72], switchgrass [73], switchgrass pellets [74], corn stover [75,76], energy sorghum [77], aspen [78] and energy cane [79]. The results showed that the adsorption process of biomass can be divided into two ranges: rapid adsorption and slow adsorption processes and EMC mainly depends on biomass type and environmental humidity.…”

“…In general, the elemental composition results can be illustrated by van Krevelen diagramsorternary graphs, which cross-plot the hydrogen:carbon atomic ratios as a function of the oxygen:carbon atomic ratios of organic materials [103]. Mann et al [79] proposed a CHO index to describe the oxidation state of organic carbon in organic materials:…”