HR: 0830h
AN: B31D-0332    [PDF]
TI: Woody Plant Invasion of Grassland: Lignin and Aliphatic Biopolymer Chemistry and Carbon Isotope Composition in Physical Fractions
AU: Gamblin, D
EM: gamblind@purdue.edu
AF: Department of Earth and Atmospheric Sciences Purdue University, 1397 Civil Engineering Bld, West Lafayette, IN 47907 United States
AU: Boutton, T
EM: boutton@neo.tamu.edu
AF: Department of Rangeland Ecology & Management, Texas A&M University, College Station, TX 77843 United States
AU: Liao, J
EM: jade@neo.tamu.edu
AF: Department of Rangeland Ecology & Management, Texas A&M University, College Station, TX 77843 United States
AU: Jastrow, J
EM: jdjastrow@anl.gov
AF: Argonne National Laboratory, Environmental Research Division,, Argonne, IL 60439 United States
AU: * Filley, T
EM: filley@purdue.edu
AF: Department of Earth and Atmospheric Sciences Purdue University, 1397 Civil Engineering Bld, West Lafayette, IN 47907 United States
AB: Significant changes in the apportionment of organic carbon in grassland and savanna soils have been document as a result of woody plant encroachment. In the Rio Grande Plains of Texas, C4 grasslands (d13C = -14 0/00) have undergone succession to trees and shrubs of a subtropical thorn woodland (d13C = -27 0/00) over the past 150 y which has resulted in increased soil organic carbon storage. Large differences in the turnover times of physical fractions in this system indicate selective preservation mechanisms which may include physical protection or inherent biochemical recalcitrance. To elucidate mechanisms of SOC sequestration during woody plant succession in this system, we are investigating the chemistry and compound-specific stable carbon isotope composition of lignin and aliphatic biopolymers in specific physical (size, density) soil fractions within a chronosequence that includes remnant grasslands (Time 0) and woody plant stands ranging in age from 10-130 y. The soil fraction data is being compared to biopolymer and isotope chemistry of the root, stem and/or leaf tissue of 20 of the dominant genus of plants in the system. Lignin phenols and suberin and cutin-derived hydroxyfatty acids are being isolated using alkaline CuO oxidation and tetramethylammonium hydroxide thermochemolysis. A comparison of the macroaggregate (greater than 250 um), microaggregate (53-250 um), and free silt and clay fractions in the oldest stand indicates that lignin is the most concentrated (organic carbon normalized values) in macroaggregates and is significantly less degraded, as determined by relative yields of oxidized and reduced lignin phenols. Additionally, the intra-aggregate silt and clay fraction from the macroaggregates contains less than half of the organic carbon normalized lignin phenols and is relatively more oxidized than what is found in the total macroaggregate pool. From these preliminary results it appears that the bulk macroaggregate pool contains the least degraded/freshest lignin of the physical fractions. This is consistent with the relatively shorter residence times determined for this fraction in this system. Continuing work includes compound specific isotope analysis of isolated lignin and hydroxyl fatty acids to elucidate biopolymer-specific turnover times which will provide important clues into the mechanisms of SOM storage and biopolymer recalcitrance.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4815 Ecosystems, structure and dynamics
SC: Biogeosciences [B]
MN: 2003 Fall Meeting