Extraction method shapes soil water-soluble organic matter composition as revealed by absorbance, fluorescence, and...

Area of Science:

• Soil Science
• Biogeochemistry
• Environmental Chemistry

Background:

• Organic matter (OM) is crucial for soil and aquatic biogeochemical cycles.
• Water-soluble organic matter (WSOM) is a mobile fraction of soil OM, often analyzed using extraction methods.
• Extraction method significantly influences the characterization of WSOM's chemical composition.

Purpose of the Study:

• To compare the effectiveness of two WSOM extraction protocols: distilled water and 0.5 M K2SO4.
• To analyze dissolved organic carbon (DOC) concentration and composition in soil extracts.
• To understand how extraction chemistry affects the interpretation of soil organic matter dynamics.

Main Methods:

• Collected 217 soil samples from 83 depth profiles across four central European regions.
• Utilized distilled water and 0.5 M K2SO4 for WSOM extraction.
• Employed absorbance and fluorescence spectroscopy with PARAFAC modeling to characterize DOC.

Main Results:

• K2SO4 extracts showed higher DOC concentrations, dominated by humic-like fluorescence, indicating more stable OM pools.
• Water extracts exhibited greater variability and stronger protein-like signals, reflecting labile, microbially-derived DOM.
• DOC concentrations generally decreased with soil depth, with water extracts showing clearer depth-related trends.

Conclusions:

• Extraction chemistry critically influences the characterization of soil WSOM and its lability.
• Water extraction highlights reactive, microbially-produced WSOM relevant to aquatic systems.
• Salt-based extraction emphasizes less bio-available, long-term terrestrial OM reservoirs.