Wednesday, November 15, 2006 - 1:30 PM

Molecular Markers for Studying Soil Organic Matter Sources and Biogeochemistry.

Steven Salisbury, Wilbur-Ellis Co., PO Box 51, Shedd, OR 97377 and Angelika Otto, Department of Physical and Environmental Sciences, 1265 Military Trail, University of Toronto, Toronto, ON M1C1A4, Canada.

Assessing soil organic matter sources in the biogeosphere is important for understanding soil organic matter turnover, carbon fluxes, and decomposition patterns.  Molecular markers or biomarkers are useful indicators for the study of organic matter dynamics because they provide insight into organic matter sources, degradation pathways, and fluxes.  Some molecular markers are organism or species specific and thus can be used to identify and quantify soil biogeochemical processes and reconstruction of past events such as past climates or disturbances such as forest fire.  This presentation will focus on molecular marker measurements by gas chromatography/mass spectrometry (GC/MS) and how this data can be used to evaluate the origin and dynamics of soil organic matter.  A case study on biomass burning (black carbon) biomarkers will be highlighted to demonstrate how molecular markers can be used to assess the quantity and distribution of thermal alteration products at a recent forest fire in Northern Alberta, Canada.  In this study, we found that terpenoid and steroid biomolecules were in part altered during incomplete combustion to aromatic, unsaturated and polar derivatives that still retained the characteristic skeleton of their precursors which facilitated source apportionment of these molecular markers.  Proposed ratios of biological precursors to aromatic (diterpenoids) or unsaturated products (steroids) indicated that the cyclic lipids in the pine wood and the soil surface horizon were highly altered.  The information from solvent extractable lipids and carbohydrates in charred soils provides valuable, source specific molecular markers for the burning of plant biomass and for tracing the biogeochemistry of charred residues in soils.  In addition, the complementarity of molecular marker methods with nuclear magnetic resonance (NMR) techniques will also be highlighted.