title: Molecular composition and biodegradability of soil organic matter: a case study comparing two new England forest types.
abstract: Soil organic matter (SOM) is involved in many important soil processes such as carbon sequestration and the solubility of plant nutrients and metals. Ultrahigh resolution mass spectrometry was used to determine the influence of forest vegetation type and soil depth on the molecular composition of the water-extractable organic matter (WEOM) fraction. Contrasting the upper 0-5 cm with the 25-50 cm B horizon depth increment, the relative abundance of lipids and carbohydrates significantly increased, whereas condensed aromatics and tannins significantly decreased for the deciduous stand WEOM. No significant abundance changes were found for the coniferous stand DOM. Kendrick mass defect analysis showed that the WEOM of the 25-50 cm B horizon was depleted in oxygen-rich and higher mass components as compared to the 0-5 cm B horizon WEOM, suggesting that higher mass WEOM components with oxygen-containing functionality show greater reactivity in abiotic and/or biotic reactions. Furthermore, using an inoculated 14-day laboratory incubation study and multivariate ordination methods, we identified the WEOM components with H:C > 1.2 and O:C > 0.5 as being correlated most strongly with biodegradability. Our findings highlight the importance of understanding soil depth differences for various forest types in the chemical composition of SOM and the processes governing SOM production and transformations to fully understand the ecological implications of changes in forest composition and function in a changing climate.
authors.affiliation: School of Food and Agriculture, University of Maine , Orono, Maine 04469-5722, United States.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Ohno
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Parr
authors.forename: Marie Cécile I
authors.initials: MC
authors.lastname: Gruselle
authors.forename: Ivan J
authors.initials: IJ
authors.lastname: Fernandez
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Sleighter
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hatcher
mesh_terms: D001673:Biodegradation, Environmental; D002244:Carbon / Q000032:analysis; D017357:Cyclotrons; D005583:Fourier Analysis; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D008970:Molecular Weight; D009511:New England; D009584:Nitrogen / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis*; D010126:Ozone / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012995:Solubility; D014197:Trees / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D009930:Organic Chemicals; D012987:Soil; D014867:Water; D010126:Ozone; D002244:Carbon; D009584:Nitrogen