Evolution of the chemical composition of Ginkgo biloba external and internal leaf lipids through senescence and litter formation Thanh Thuy Nguyen Tu a,b, *, Sylvie Derenne b , Claude Largeau b , Andre Mariotti a , Herve Bocherens a a Laboratoire de Bioge Âochimie Isotopique, Universite  Paris VI, INRA-CNRS UMR 7618, Case courrier 120, 4 Place Jussieu, 75 252 Paris Cedex 05, France b Laboratoire de Chimie Bioorganique et Organique Physique, Ecole Nationale Supe Ârieure de Chimie de Paris, CNRS UMR 7573, 11 Rue Pierre et Marie Curie, 75 231 Paris Cedex 05, France Received 7 June 1999; accepted 18 October 2000 (returned to author for revision 3 May 2000) Abstract External and internal lipids were analysed in fresh, senescent and litter leaves of Ginkgo biloba to derive qualitative and quantitative information on the changes that occur during the very early stages of diagenesis, and to identify potential biomarkers of the only living Ginkgoale. Analysis of fresh leaves led to the identi®cation of additional com- pounds, including several series of phenolic constituents, and showed dierences between the external and internal lipids (absence/presence of some components, relative abundances and distributions of some series). Pronounced dif- ferences concerned with the evolution of content (as wt.% of whole leaves) were observed between the internal lipids (regular decrease from fresh to senescent and to litter leaves) and the external lipids (no signi®cant changes in content). Molecular studies showed variations in the relative abundances and distributions of most constituents of G. biloba leaf lipids which re¯ect dierent degrees of stability during the ®rst stages of diagenesis. It also appeared that (i) the phe- nolic components and the co-occurrence of a-tocopherol and nonacosan-10-ol could be useful biomarkers of G. biloba, and (ii) most of the internal lipids continue to be exported to the leaf surface where they are further degraded during senescence and litter formation. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Ginkgo biloba; Leaf lipids; Early degradation; Litter leaves; Senescent leaves 1. Introduction Higher plant detritus constitutes a large and con- tinually renewed pool of reactive organic matter in estuarine and coastal marine environments, and higher plants are a major contributor of organic matter to sediments (Tissot and Welte, 1984). The nature and distributions of lipid components is often used to dierentiate higher plant organic matter from bacterial or algal organic matter, in marine environments (e.g. Goutx et al., 1990; Harada et al., 1995; Zegouagh et al., 1996), ¯uvial environments (e.g. Jae et al., 1995) or lacustrine environments (e.g. Cranwell, 1984; Rieley et al., 1991). Nevertheless, while the lipid composition of modern organisms has been extensively investigated, in order to identify molecular biomarkers, the very early stages of their diagenesis has only been studied recently (e.g. de Leeuw et al., 1995; Jae et al., 1996). The pre- sent study focuses on the examination of changes in leaf lipids of Ginkgo biloba through the early stages of degradation (fresh, senescent and litter leaves) in order 0146-6380/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(00)00152-2 Organic Geochemistry 32 (2001) 45±55 www.elsevier.nl/locate/orggeochem * Corresponding author at Laboratoire de PaleÂobotanique et Pale oe cologie, Universite Paris VI, 12 Rue Curier, 75 005 Paris, France. Fax: +33-1-44-276513. E-mail address: thanh-thuy.nguyen- tu@snv.jussieu.fr (T.T. Nguyen Tu).