Advanced Solvent Based Methods for Molecular Characterization of Soil
Organic Matter by High-Resolution Mass Spectrometry
- Publication date
- Publisher
Abstract
Soil organic matter (SOM), a complex,
heterogeneous mixture of
above and belowground plant litter and animal and microbial residues
at various degrees of decomposition, is a key reservoir for carbon
(C) and nutrient biogeochemical cycling in soil based ecosystems.
A limited understanding of the molecular composition of SOM limits
the ability to routinely decipher chemical processes within soil and
accurately predict how terrestrial carbon fluxes will respond to changing
climatic conditions and land use. To elucidate the molecular-level
structure of SOM, we selectively extracted a broad range of intact
SOM compounds by a combination of different organic solvents from
soils with a wide range of C content. Our use of electrospray ionization
(ESI) coupled with Fourier transform ion cyclotron resonance mass
spectrometry (FTICR MS) and a suite of solvents with varying polarity
significantly expands the inventory of the types of organic molecules
present in soils. Specifically, we found that hexane is selective
for lipid-like compounds with very low O/C ratios (<0.1); water
(H<sub>2</sub>O) was selective for carbohydrates with high O/C ratios;
acetonitrile (ACN) preferentially extracts lignin, condensed structures,
and tannin polyphenolic compounds with O/C > 0.5; methanol (MeOH)
has higher selectivity toward compounds characterized with low O/C
< 0.5; and hexane, MeOH, ACN, and H<sub>2</sub>O solvents increase
the number and types of organic molecules extracted from soil for
a broader range of chemically diverse soil types. Our study of SOM
molecules by ESI FTICR MS revealed new insight into the molecular-level
complexity of organics contained in soils. We present the first comparative
study of the molecular composition of SOM from different ecosystems
using ultra high-resolution mass spectrometry