Adsorptive Fractionation of Water-Extractable Organic Matter on Iron (oxy)Hydroxide: A FT-ICR-MS Study.

Soil organic matter (SOM) is involved in many important soil processes such as carbon sequestration and the solubility of plant nutrients and metals. Previously, ultrahigh resolution mass spectrometry was used to show that soil depth exerted a strong effect on the molecular composition of the water-extractable organic matter (WEOM) fraction. Here, laboratory studies investigated the adsorptive fractionation of WEOM onto FeOOH as a potential pathway for the changing SOM chemical composition with soil depth. Ultrahigh resolution FT-ICR mass spectrometry show that aromatic and N-containing aliphatic molecules were preferentially adsorbed onto the FeOOH. Our findings highlight the importance of understanding the chemical composition of SOM and the processes governing SOM production and transformations to fully understand the ecological processes controlling soil C stabilization.