HR: 1340h
AN: B43A-0236    [Abstracts]
TI: Changes to Lignin Phenol and Hydroxy Alkanoic Acid yStable Carbon Isotope Composition and Concentration in ySoil Fractions from a Grassland/Woodland Conversion in ya Subtropical Savannay
AU: * Filley, T
EM: filley@purdue.edu
AF: Department of EAS, Purdue University, 550 Stadium Mall Dr, West Lafayette, IN 47907 United States
AU: Gamblin, D
EM: gamblind@purdue.edu
AF: Department of EAS, Purdue University, 550 Stadium Mall Dr, West Lafayette, IN 47907 United States
AU: Boutton, T
EM: boutton@acs.tamu.edu
AF: Department of Rangeland Ecology and Management Texas A&M University , 2126 TAMU, College Station, TX 77843-2126 United States
AU: Liao, J
EM: redjade_liao@yahoo.com
AF: Department of Rangeland Ecology and Management Texas A&M University , 2126 TAMU, College Station, TX 77843-2126 United States
AU: Jastrow, J
EM: jdjastrow@anl.gov
AF: Environmental Research Division Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AB: The response of soil organic carbon (SOC) pools to changes in land cover during woody yplant encroachment is an issue of great importance to soil carbon modeling as grassland ysoils represent a major Earth C stock. Bulk assessments of carbon turn over in soils can ybe obtained in systems where C4 plants are being replaced by C3 trees using stable yisotope modeling along a chronosequence. Few SOC studies, however, approach the yquestion of carbon storage and turn over at the compound specific level even though ybiopolymers turnover at vastly different rates and have selective affinities for long term ypreservation. Defining what compound classes represent relatively recalcitrant or labile ypools can be made in such systems where intrinsic differences in stable isotope ycomposition and molecular chemistry are very large. We quantified changes in lignin yphenol and hydroxyl alkanoic acid chemistry and stable carbon isotope composition of ysize and density fractionated soil from the Rio Grande Plains of Texas where C4 ygrasslands (δ13C = -14%) have undergone succession to subtropical thorn woodland ydominated by C3 trees/shrubs (δ13C = -27%) over an 80 year chronosequence. yComparison of the extant of conversion of the grassland SOM to C3 carbon by bulk SOC yisotope modeling to that obtained using compound specific isotope analysis of lignin yphenols in the microaggreagate (53-250 microns), macroaggregates (>250 microns), and ythe microaggregated particulate organic matter (<1.8 g/cc) demonstrates faster turn over yfor the average bulk pool than for lignin. Additionally, p-hyroxy lignin converts to C3 at yabout twice the rate as does vanillyl and syringyl lignin phenol pools reflecting both ydifferences in input rate and ease by which the different pools can be degraded by ymicrobes. The relative extent of turn over between the physical fractions remained the ysame in the two analyses with macroaggrgates>microaggregated pom>microaggregates. yThis work adds to a growing body of the importance of compound specific isotope yanalyses to record ecosystem shifts in soils in compounds that have the potential for long yterm storage.y
DE: 0330 Geochemical cycles (1030)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1610 Atmosphere (0315, 0325)
SC: Biogeosciences [B]
MN: Fall Meeting 2005