HR: 10:50h
AN: B52A-02    [Abstracts]
TI: Molecular Investigation of the Short-term Sequestration of Natural Abundance $^{13}$C\$\-$labelled Cow Dung in the Surface Horizons of a Temperate Grassland Soil
AU: * Dungait, J
AF: University of Bristol, Organic Geochemistry Unit Biogeochemistry Research Centre School of Chemistry Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Bol, R
EM: roland.bol@bbsrc.ac.uk
AF: Institute of Grassland and Environmental Research, Soils Science and Environmental Quality Team North Wyke, Okehampton, EX20 2SB United Kingdom
AU: Evershed, R P
EM: r.p.evershed@bristol.ac.uk
AF: University of Bristol, Organic Geochemistry Unit Biogeochemistry Research Centre School of Chemistry Cantock's Close, Bristol, BS8 1TS United Kingdom
AB: An adequate understanding of the carbon (C) sequestration potential of grasslands requires that the quantity and residence times of C inputs be measured. Herbivore dung is largely comprised of plant cell wall material, a significant source of stable C in intensively grazed temperate grassland ecosystems that contributes to the soil carbon budget. Our work uses compound-specific isotope analysis to identify the pattern of input of dung-derived compounds from natural abundance $^{13}$C$/-$labelled cow dung into the surface horizons of a temperate grassland soil over one year. C4 dung ($\delta$$^{13}$C $\-$12.6 $\permil$) from maize fed cows was applied to a temperate grassland surface ($\delta$$^{13}$C $\-$29.95 $\permil$) at IGER-North Wyke (Devon, UK), and dung remains and soil cores beneath the treatments collected at {\t} = 7, 14, 28, 56, 112, 224 and 372 days. Bulk dung carbon present in the 0$\-$1 cm and 1$\-$5 cm surface horizons of a grassland soil over one year was estimated using $\Delta$$^{13}$C between C$_{4}$ dung and C$_{3}$ dung, after Bol {\et al.} (2000). The major biochemical components of dung were quantified using proximate forage fibre analyses, after Goering and Van Soest (1970) and identified using `wet' chemical and GC-MS methods. Plant cell wall polysaccharides and lignin were found to account for up to 67 {%} of dung dry matter. Hydrolysed polysaccharides were prepared as alditol acetates for analyses (after Docherty {\et al.}, 2001), and a novel application of an off-line pyrolysis method applied to measure lignin-derived phenolic compounds (after Poole & van Bergen, 2002). This paper focuses on major events in the incorporation of dung carbon, estimated using natural abundance $^{13}$C{\-}labelling technique. This revealed a major bulk input of dung carbon after a period of significant rainfall with a consequent decline in bulk soil $\delta$$^{13}$C values until the end of the experiment (Dungait {\et al.}, submitted). Findings will be presented revealing contribution of plant cell wall polysaccharides and lignin to these bulk $\delta$$^{13}$C values, and their potential for sequestration considered. References: Bol, R., Amelung, W., Friedrich, C. Ostle, N. (2000). Tracing dung-derived carbon in temperate grassland using $^{13}$C natural abundance measurements. Soil Biology and Biochemistry, 32, 1337-1343. Goering and Van Soest (1970). Forage fibre analysis (apparatus, reagents, procedures and some applications). In: USDA-ARS Agricultural Handbook, 379. U. S. Government Printing Office, Washington D.C. Docherty, G., Jones, V. and Evershed, R.P. (2001). Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry $\delta$$^{13}$C analysis of small polyfunctional compounds. Rapid Communications in Mass Spectrometry, 15, 730-738. Poole, I. & van Bergen, P. F. (2002). Carbon isotope ratio analysis of organic moieties from fossil mummified wood: establishing optimum conditions for off-line pyrolysis extraction using gas chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry, 16, 1976-1981. Dungait, J. A. J., Bol, R. and Evershed, R.P. (submitted). The Fate of Dung Carbon in Temperate Grassland Soil: 1. Preliminary Findings Based on Bulk Stable Carbon Isotope Determinations. Isotopes in Health and Environmental Studies
UR: http://www.chm.bris.ac.uk/org/evershed/
DE: 1040 Isotopic composition/chemistry
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting