Unraveling the structural components of soil humin by use of solution-state nuclear magnetic resonance spectroscopy.
Humin is the most recalcitrant and least understood fraction of soil organic matter. By definition, humin is that fraction not extracted by traditional aqueous alkaline soil extractants. Here we show that > or = 70% of the traditional humin fraction is solubilized when 0.1 M NaOH + 6 M urea and dimethyl sulfoxide (DMSO) + 6% H2SO4 are used in series after conventional extraction. Multidimensional solution-state NMR is applied in this study to gain an understanding of the major constituents present in these "solubilized humin fractions". The spectra indicated strong contributions from five main categories of components, namely, peptides, aliphatic species, carbohydrates, peptidoglycan, and lignin. Diffusion edited spectroscopy indicated that all species are present as macromolecules (or stable aggregate species). Although the distribution of the components is generally similar, peptidoglycan is present at significant levels supporting a higher microbial contribution to humin than to humic and fulvic fractions. The abundance of plant- and microbial-derived materials found does not exclude "humic" materials (e.g., oxidized lignin) or the presence of novel compounds at lower concentrations but suggests that a large proportion of humin is formed from classes of known compounds and parent biopolymers.
Simpson
Andre J
AJ
Department of Chemistry, University of Toronto, Scarborough Campus, Toronto, Ontario, MIC 1A4 Canada. andre.simpson@utoronto.ca
Song
Guixue
G
Smith
Emma
E
Lam
Buuan
B
Novotny
Etelvino H
EH
Hayes
Michael H B
MH
D001578:Benzopyrans / Q000032:analysis; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004784:Environmental Monitoring; D006812:Humic Substances / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D012972:Sodium Hydroxide / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D012995:Solubility; D012996:Solutions / Q000737:chemistry*; D013464:Sulfuric Acids / Q000737:chemistry; D014508:Urea / Q000737:chemistry
D001578:Benzopyrans; D006812:Humic Substances; D012989:Soil Pollutants; D012996:Solutions; D013464:Sulfuric Acids; C001861:humin; D012972:Sodium Hydroxide; D014508:Urea; C033158:sulfuric acid; C005023:fulvic acid; D004121:Dimethyl Sulfoxide