HR: 14:10h
AN: B53D-02    [Abstracts]
TI: Dynamics of Biopolymer Turnover in Soil Physical Fractions Following Land-Cover yChange in a Subtropical Savanna
AU: * Filley, T R
EM: filley@purdue.edu
AF: Department of Earth and Atmospheric Sciences Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47906 United States
AU: Gamblin, D
EM: gamblind@purdue.edu
AF: Department of Earth and Atmospheric Sciences Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47906 United States
AU: Wang, Y
EM: wang119@purdue.edu
AF: Department of Earth and Atmospheric Sciences Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47906 United States
AU: Liao, J
EM: jade@neo.tamu.edu
AF: Department of Rangeland Ecology and Management Texas A&M University, 2126 TAMU, College Station, TX 77843 United States
AU: Boutton, T
EM: boutton@neo.tamu.edu
AF: Department of Rangeland Ecology and Management Texas A&M University, 2126 TAMU, College Station, TX 77843 United States
AU: Jastrow, J
EM: jdjastrow@anl.gov
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AB: Changes in the apportionment of organic carbon and nitrogen among soil physical yfractions following land-cover shifts are of critical importance to the debate surrounding ythe capacity of terrestrial ecosystems to store or release greenhouse gases. For example, ythe difference between the mean residence times (MRTs) of light particulate organic ymatter (POM) vs. silts and clays is typically quite large, with silt and clay associated yorganic matter having the longest MRTs and the greatest likelihood to contribute to long yterm carbon storage. A few studies in agricultural and forest systems have demonstrated ythat biopolymer chemistry also varies along physical, as well as density, fractionation ygradients. We quantified changes in biopolymer (lignin, suberin and cutin, and yhydrolysable amino acids) chemistry of size and density fractionated soil from the Rio yGrande Plains of Texas where C4 grasslands (d13C = -14 %) have undergone succession yto subtropical thorn woodland dominated by C3 trees/shrubs (d13C = -27 %) over the ypast 150 years. This natural isotopic distinction was used to determine MRTs of free ylight organic matter (density less than 1.0 g/cc), macroaggregate (greater than 250 um), ymicroaggregate (53-250 um) and silt+clay (less than 53 um) fractions (see Liao et al., ythis session) which were then related to their specific biopolymer chemistries. Our yresults illustrate that lignin and aliphatic biopolymers (as measured by hydroxyl fatty yacids) are apportioned differently among size/density fractions and along the successional ychronosequence. Lignin is incorporated into all soil fractions soon after woody yencroachment, whereas aliphatic components are slow to be incorporated in the silt and yclay fractions. The lignin components that do become associated with silts and clays are, yin general, highly oxidized. Differences in foliar chemistry among the plant sources yindicate selective movement of leaf cutins into POM, macro- and microaggregate yfractions, but not into free or intra-aggregate silts and clays. Selected analyses of silt and yclay fractions for hydrolysable amino acids showed differences along the ychronosequence, with total hydrolysable amino acids comprising 30-45% of total ynitrogen. It is possible that amino and phenolic compounds are tightly bound to the silts yand clays (the fractions with the longest MRT) and repel the more hydrophobic and less ywater soluble cutin and suberin monomers, thereby restricting turnover. These results yprovide new insights regarding the interactions between soil structure, chemistry, yturnover, and preservation of soil organic matter. y
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting