HR: 0800h
AN: B11A-1020    [Abstracts]
TI: Characterization of Soil Organic Carbon Using Pyrolysis-GC/MS Along a Hawaiian Precipitation Gradient.
AU: * Kelleher, J A
EM: jkelleher@stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences Braun Hall, Bldg. 320, Stanford, CA 94305 United States
AU: Schuur, E A
EM: tschuur@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall PO Box 118526, Gainsville, FL 32611-8526 United States
AB: The net gain or loss of soil organic carbon (SOC) from large belowground stores in many ecosystems can dramatically influence the global carbon cycle. A more detailed understanding of the link between SOC-cycling mechanisms and ecosystem scale observations is necessary to place soils into the framework of greater environmental change. This study examines carbon cycling as a function of precipitation using pyrolysis-GC/MS measurements and paired ¹³C and ¹⁵N isotopic analyses. Paired with comprehensive isotopic data, this pyrolysis-GC/MS study provides an opportunity to study the mechanisms of decomposition and carbon cycling both intra- and intersites. Sites from a natural precipitation gradient in Hawaii (MAP range from 2200 to >5000mm/yr) show a general increase in C storage linked to decreased net primary productivity and decomposition as a function of increasing rainfall. Soils were separated using standard density fractionation procedures into four fractions: roots, organics (<1.7g/cc), amorphous soil minerals (1.7g/cc<sample<2g/cc), and other soil minerals (>2g/cc). The root fraction was enriched in ¹³C and depleted in ¹⁵N, while the other mineral fractions were more enriched in ¹⁵N, characteristic of a higher degree of decomposition. The chemical composition of organic matter in these fractions was further analyzed with pyrolysis-GC/MS, where the pyrograms are clearly distinguishable between fractions. Preliminary results from root spectra show consistent, and relatively large, amounts of acetic acid, furfural and vinylguaiacol. Both the organic and amorphous mineral fractions show a wide range of dominant compounds, however, the amorphous fractions trend toward preservation of increasing amounts of aliphatic compounds with increasing precipitation. The other mineral fraction showed characteristic high concentrations of cellulose derivatives including compounds like furfural and furan, with a consistent absence of other more common lignin derivatives except benzaldehyde. This work suggests a partitioning of root-derived carbon, with root lignin components cycling rapidly and more recalcitrant, cellulosic signature translating to the mineral fraction. This study ultimately helps characterize the preferential accumulation of particular compounds that may drive observed increases in C storage along this rainfall gradient in Hawaii.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005