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Fractionation of hydrogen isotopes between source water, leaf water and miliacin in Panicum miliaceum grown under controlled conditions.

Abstract : D analyses of organic compounds preserved in sedimentary archives affords new perspectives in tracking past climates. The rationale is that the D of these fossil molecules records the climatic conditions in which they were produced by plants and is stable when transported and archived in sediments. Numerous studies focus on n-alkyl lipids (n-alkanes and n-acids) that have the advantage of being ubiquitous in sediments. Conversely, the large range of organisms being able to produce these compounds, living in distinct environments and with potentially different fractionations of hydrogen isotopes during biosynthesis, limits the interpretation that can be achieved from these data. Studies presently suggest that several shifts in compound-specific D values in the sedimentary record could either be attributed to vegetation or climatic changes. We recently detected in the sediments of lake Le Bourget miliacin (olean-18-en-3ol ME), which could be related to a single species: broomcorn millet (Panicum miliaceum; Jacob et al., 2008). Due to the species specificity of miliacin, its D values are thought to solely record climatic changes and would not be affected by mixing between compounds produced by distinct biological sources. Our overarching objective is to reconstruct the hydrological variability that affected the French Alps during the Bronze age by determining the D of sedimentary miliacin and relating this value to environmental parameters. Our first step has been to quantify the fractionations of hydrogen isotopes from source waters to miliacin synthesis. For this purpose, we cultivated P. miliaceum plants under controlled conditions in climatic chambers with 4 different source water D (five replicates for each condition). Miliacin was extracted and purified from leaves, stems and seeds, and then quantified by GC-MS. Miliacin D values were determined on a TraceGC chromatograph coupled to a DeltaV Advantage irMS through an Isolink interface and a Conflo IV system by co-injecting a series of n-alkanes of known D values (Arndt Schimmelmann, Indiana University). Leaf water D and 18O were determined after cryogenic distillation for 18O on an IRMS (Isoprime) coupled to an aquaprep and for D an IRMS PyrOH (Isoprime) coupled to an elemental analyser EuroVector. The results allowed us to establish the net hydrogen isotopic fractionation between environmental waters and miliacin and the fractionation attributable to the biosynthetic pathways. References Jacob, J., Disnar, J.R., Arnaud, F., Chapron, E., Debret, M., Lallier-Vergès, E., Desmet, M., Revel-Rolland, M. 2008. Journal of Archaeological Science 35, 814-820. Sachse D., Radke J., Gleixner G. 2004. Geochimica et Cosmochimica Acta 68, 23: 4877-4889.
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Submitted on : Tuesday, September 24, 2013 - 11:13:18 AM
Last modification on : Saturday, September 19, 2020 - 4:44:59 AM

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  • HAL Id : insu-00865271, version 1

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Nicolas Bossard, Jérémy Jacob, Valery T. Terwilliger, Thierry Bariac, Claude Le Milbeau, et al.. Fractionation of hydrogen isotopes between source water, leaf water and miliacin in Panicum miliaceum grown under controlled conditions.. Studium Conference : "Hydrogen Isotopes as Environmental Recorders, Sep 2011, Orléans, France. ⟨insu-00865271⟩

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