Huang2008OG

Distributionofaliphaticdes-A-triterpenoidsintheDajiuhupeatdeposit,southernChinaXianyuHuanga,*,ShuchengXieb,ChuanlunL.Zhangc,DanJiaoa,JunhuaHuangb,JianxinYua,FangJina,YanshengGuaaKeyLaboratoryofBiogeologyandEnvironmentalGeologyofMinistryofEducation,ChinaUniversityofGeosciences,Wuhan,Hubei430074,ChinabStateKeyLaboratoryofGPMR,ChinaUniversityofGeosciences,Wuhan430074,ChinacDepartmentofMarineSciences,TheUniversityofGeorgia,Athens,GA30602,USAarticleinfoArticlehistory:Received13March2008Receivedinrevisedform18July2008Accepted11August2008AvailableonlinexxxxabstractAliphaticdes-A-triterpenoidshavebeententativelyassignedinsamplestakenfroma260cmthickpeatsequencefromtheDajiuhuBasinofsouthernChinausinggaschroma-tography–massspectrometry(GC–MS).Thecompounds,possessingthecarbonskeletonsofoleanane,ursaneorlupane,aregenerallyconsideredasthemicrobialdegradationprod-uctsofplanttriterpenoidsunderanoxicconditions.Abundantaliphaticdes-A-triterpenoidswereobservedonlyinpeatsamplesduringthetransitionalperiodfromthelastglaciationtotheearlyHolocene(9.5–11.6cal14CkaBP).Amongthese,des-A-lupaneistheonlysat-uratedringA-degradedcompound,whilstmono-anddi-unsaturateddes-A-triterpenesaredominatedbyoleananeandursanederivatives.Themono-anddi-unsaturateddes-A-triterpenesshowastrongcorrelation(R20.94)inabundance,indicatingthattheymaybederivedfromthesamesourceorprocess.Des-A-lupaneshowsnocorrelationinabun-dancewiththemono-ordi-unsaturateddes-A-triterpenes(R20.25)andmaybederivedfromadifferentsourceorprocessinthecatchment.Theperiodwithabundantaliphaticdes-A-triterpenoidscorrespondstotheintervalwithrelativelyhighsedimentationrate(0.3mmperyear).Thesedataindicatethattheabundanceofaliphaticdes-A-triterpe-noidsintheDajiuhupeatdepositintheearlyHolocenemayresultfromtheprevailingreducingconditionsinthewatertableorsurficialsedimentand/orrapidpreservationoftheearlydiageneticproducts.Ourstudyhighlightsthepotentialapplicationofdes-A-triter-penesinthereconstructionofpalaeoenvironmentsbasedonpeatsequences.2008ElsevierLtd.Allrightsreserved.1.IntroductionTheexcellentpreservationpotentialofpeatdepositsmakesthemuniqueinretaininglipidcompounds.Recentstudiesofpeatlipidsshowthatmoreandmorelipidbio-markersandassociatedproxiescanbeexploredtoreflectpalaeoenvironmentalchangesinpeatlands(Fickenetal.,1998;Baasetal.,2000;Nottetal.,2000;Pancostetal.,2000,2002,2003;Xieetal.,2000,2004;Avsejsetal.,2002;Zhouetal.,2005;Nicholsetal.,2006;NicholsandHuang,2007;Zhengetal.,2007).Asanexample,themediumchainlengthn-C23alkaneisspecificforthewaxcoatingofleavesofSphagnumspp.,themostcommonplantinpeatbogs(Nottetal.,2000,2006;Pancostetal.,2002)anditsdistribution,andcarbonandhydrogeniso-topescanserveasindicatorsofclimatechange(Xieetal.,2000;Pancostetal.,2002;Nicholsetal.,2006).Inaddition,someothercompoundssuchaslongchainn-alkanes,n-alcoholsandfattyacidshavebeenemployedtorecordchangesintheAsianpalaeo-monsooninChina(Zhouetal.,2005;Zhengetal.,2007).Des-A-triterpenespotentiallypreserveinformationaboutdiageneticprocessesandcanserveasindicatorsofenvironmentalchange.Variousaliphaticdes-A-triterpe-noidshavebeenfoundinpeatdeposits(delRioetal.,0146-6380/$-seefrontmatter2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.orggeochem.2008.08.002*Correspondingauthor.Fax:[phone].E-mailaddress:[e-mail](X.Huang).OrganicGeochemistryxxx(2008)xxx–xxxContentslistsavailableatScienceDirectOrganicGeochemistryjournalhomepage::Huang,X.etal.,Distributionofaliphaticdes-A-triterpenoidsintheDajiuhupeat...,Org.Geochem.(2008),doi:10.1016/j.orggeochem.2008.08.0021992;Dehmer,1995;DuanandMa,2001),lakesediments(Jafféetal.,1996;PrartonoandWolff,1998;Ottoetal.,2005;Bechteletal.,2007;Jacobetal.,2007)andancientsediments(LoganandEglinton,1994;Dellwigetal.,1998;Milleetal.,2006;vanDongenetal.,2006).Com-poundswitholeanane,ursaneandlupanecarbonskeletonsdominateinthesesediments.Theyaregenerallyconsid-eredasdiagenetictransformationproductsofterrestrialtriterpenoids,principallymediatedbymicrobialactivity(e.g.Corbetetal.,1980;Trendeletal.,1989;Milleetal.,2006;Jacobetal.,2007).InaninvestigationofthelipidsofaBrazilianfreshwaterlake,forexample,thedistributionpatternsofaliphaticandaromaticdes-A-triterpenoidsandtriterpenoidsweresuccessfullyappliedtoreconstructthepalaeovegetationandpalaeoenvironmentchangesoverthepast18ka(Jacobetal.,2007).Inarecentstudy,weobservedauniquedistributionofaliphaticdes-A-triterpenoidsintheDajiuhupeatdeposit,ahighabundanceofthesecompoundsonlyhappeningbe-foretheearlyHolocenehorizons.Here,wetrytofindoutpossiblemechanismsresponsibleforsuchaspecificdistributionpattern,whichmaypromotethepotentialapplicationofdes-A-triterpenoidsinpalaeoenvironmentalreconstruction.2.Materialsandmethods2.1.SamplingThesampleswerecollectedfromtheDajiuhuBasin(N312805000,E1100000900)intheShennongjiaforestryre-gion,Hubeiprovince,southernChina.Thissub-alpineba-sinhasanaltitudeof1757mabovesealevel.Thepeatdepositextendsoveranareaofabout16km2andhasathicknessof260c