Table 1.
Number weighted (Mean #) and magnitude-weighted mean (Mean w) properties for SOM extracts from a simulated soil warming experiment.
The CHO index was calculated as (2×[O]–[H])/[C].
Fig 1.
van Krevelen diagram of the compound classes associated with the H:C and O:C-coordinate plane and CHO Index plot with N:C coordinate.
(a) The CHO index, , is plotted along the top and right edges of the van Krevelen diagram to illustrate their relationships and associated compound classes of organic matter assigned by Kim et al. [42]. (b) Illustration of a van Krevelen diagram for a water-soluble SOM sample (WSF0) extracted from an Arctic soil. Colored symbols represent different molecular components plotted in (c), which is a CHO index plot with molecular components binned according to N:C ratio: N:C = 0 (gray circles), 0 < N:C ≤ 0.1 (red triangles), 0.1 < N:C ≤ 0.2 (blue squares), 0.2 < N:C (green diamonds); Compounds with similar N:C are localized to distinct regions of the van Krevelen diagram in (b).
Fig 2.
Molecular distribution of extracted SOM compounds from a 40-day soil warming incubation experiment.
(a) Box-and-whisker plots of the mass distribution of SOM compounds, including the base-soluble fraction (BSF) at day 0 (BSF0) and day 40 (BSF40) and the water-soluble fraction (WSF) at day 0 (WSF0) and day 40 (WSF40). (b and c) van Krevelen diagram along with CHO index showing the molecular distribution of WSF SOM compounds before (b) and after (c) incubation. (d) Percentages of molecular formulae identified with CHO index values between -2 and 2 before and after soil incubation and are normalized to the total number of formulae displayed in (b) and (c). Compound classes are labeled above colored bars as follows: (A) lipids, (B) unsaturated hydrocarbons, (C) peptides, (D) aminosugars, (E) carbohydrates, (F) lignin, (G) condensed hydrocarbons, (H) tannins.
Fig 3.
Illustration of the molecular formulae that were either degraded (grey color) or produced (orange color) in the WSF SOM during the 40-day incubation experiment.
(a) van Krevelen diagram along with CHO index showing the molecular formulae that were either degraded (grey color) or produced (orange color) in the WSF SOM after incubation. (b) CHO Index plots of the number of molecular formulae that were either disappeared in the WSF after incubation (normalized to the total of 816 formulae) or (c) produced after incubation (normalized to the total of 212 formulae).
Fig 4.
Heatmaps for CHO index as a function of molecular mass of extracted SOM compounds before and after the soil warming experiment.
The color bar represents the relative abundance of compounds identified in each of the SOM extract: (a) WSF0, (b) WSF40, (c) BSF0, and (d) BSF40. A positive correlation between CHO index and mass can be observed for mass > 600 Da.
Fig 5.
Heatmaps for CHO index as a function of the number of N atoms in extracted SOM compounds identified in (a) WSF0, (b) WSF40, (c) BSF0, and (d) BSF40.
The color bar represents the relative abundance of compounds identified in each of the extract. Note the “island” formations observed for even numbers of N atoms in the BSF samples.