HR: 1340h
AN: B13C-0254    [Abstracts]
TI: Relating Pyrolysis GC-MS to Traditional Soil Organic Matter Characterization: a Comparative Study Across a Landscape.
AU: * Kelleher, J A
EM: kelleher@colorado.edu
AF: University of Colorado, Department of Geosciences CB 399 2200 Colorado Ave. , Boulder, CO 80309 United States
AU: Carrasco, J J
EM: carrasco@colorado.edu
AF: University of Colorado, Department of Geosciences CB 399 2200 Colorado Ave. , Boulder, CO 80309 United States
AU: Neff, J C
EM: neffjc@colorado.edu
AF: University of Colorado, Department of Geosciences CB 399 2200 Colorado Ave. , Boulder, CO 80309 United States
AB: Ecosystem scale soil organic matter studies commonly involve measurements such as physical or chemical separations to bulk soil elemental estimates, however, these measurements provide limited information about SOM structure and how it varies across landscapes. To bridge the gap between molecular-scale and pool-based understanding of SOM dynamics, we compared soil density fractionation and chemical digestion techniques to more detailed pyrolysis GC-MS measurements. Composite soil samples from 0-10 cm were collected from four sites with observably different soil characteristics along the Front Range in Colorado: aspen grove, spruce-fir forest, and alpine dry and wet meadows. Samples were separated into heavy, light, and water fractions (slow, intermediate, and fast SOM turnover pools, respectively) using a 1.8 g/mL density fractionation. Non-polar extractives, polar extractives, cellulose, and lignin abundances were determined using a standard method for organic matter digestion. Significant differences were absent between sites for all density derived components as well as the non-polar and polar extractives. The spruce-fir SOM, however, showed higher % lignin and lower % cellulose compared to all other sites. We measured lignin, polysaccharide, and long-chain aliphatic derivatives using pyrolysis GC-MS and then compared relative abundances using principal component analysis. Spruce-fir SOM was distinguished by the high relative abundance of lignin derivatives that parallels observed higher % lignin by digestion. The dry and wet meadow SOM was distinguished by the relative abundance of long-chain aliphatic compounds. While the density and chemical fractionations were unable to fully distinguish these soils apart, pyrolysis GC-MS provided more detailed information about the chemical composition of SOM across different ecosystems.
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting