A Novel Method for Analyzing Dissolved Organic Matter in Soils

Soils and sediments hold the most carbon in land ecosystems, primarily as mineral-bound or solid matter. Within these, dissolved organic matter (DOM) is a minor but highly active substance aiding in soil cohesion, carbon storage, and the global carbon cycle. Essential for microbial energy and plant nutrition, DOM also transports pollutants and signals environmental changes. We developed a novel method for analyzing dissolved organic matter (DOM) in the intricate matrices of soil environments. This novel approach represents a significant advancement in the quantification and characterization of soil organic matter (SOM), establishing essential methodological foundations for delving into the carbon cycle within soils. By incorporating Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with induction-based nano-spray Ionization, we were able to dissect the composition of DOM within interstitial waters meticulously. The level of detail achieved uncovered nearly 10,000 distinct DOM species from less than 1 µL of sample, which is only 0.01% of the sample size required by the conventional method. These insights reveal that current models may vastly underestimate the heterogeneity of DOM. Soil DOM was not dominated by lignin-like or CRAM compounds, as determined using the conventional method. The novel method revealed more peptide/carbohydrate-like compounds, highly condensed aromatics, and more than double the number of CHNO compounds. A more complete understanding of DOM will allow us to elucidate the biogeochemical processes of nutrient and DOM. The implications of this research expand our comprehension of DOM diversity and contribute a theoretical basis for subsequent exploration of carbon cycling within soil and sedimentary contexts.