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1、22SaltallocationduringleafdevelopmentandleaffallinmangrovesW.JohnCram*())PeterG.Torr*DerekA.Rose+*DepartmentofBiologicalandNutritionalSciences,UniversityofNewcastle,NewcastleuponTyne,NE17RU,UK.+DepartmentofAgriculturalandEnvironmentalSciences,UniversityofNewcastle,NewcastleuponTy
2、ne,NE17RU,UKw.j.cram@ncl.ac.ukFax:+441912228684Phone:+441912227886PresentedattheInternationalSymposiumonMangroves:Evolution,PhysiologyandConservation.TheUniversityofTokyo,Tokyo,Japan10-12July2001.AbstractBytakingsamplesalongindividualbranchesandmeasuringleafsize,thicknessandNa+an
3、dK+concentrations,wehaveshowninBruguieracylindrica,AvicenniarumphianaandAvicenniamarinathattherearetwophasesofsaltaccumulationbyleaves.Thisisconfirmedbyre-analysisofpublisheddataforotherspecies.Thefirstphaseisarapidincreaseinleafcontentasitgrowsfrombudtomaturity,thesecondisaslowe
4、rbutcontinuouschangeinquantityintheleaf,viachangesinionconcentrationand/orinleafthickening.Leafthickeningmostnotbeoverlookedin22estimatingchangesinleafcontentswithage.Generally,leafNa+contentincreasessignificantly,andK+contentfallsslightly.MangroveleavesthuscontinueassinksforNa+t
5、hroughouttheirlifetime.Attheendofaleaf’slife,justbeforeabscission,noburstofsaltaccumulationhasbeenfound.Yellow,senescentleavesdonothavehigherNa+thanoldgreenones.Wepointoutthatleafdropinvolveslosingbothsaltandbiomass,notjustsalt,andhencedoesnotreducethesaltconcentrationintheplant.
6、Weconcludethatleafdropisnotasaltexcretionmechanism,butissimplythepointintimeatwhichtheleafceasestoaccumulatesalt.Usingasimplemodel,thecontributiontosaltaccumulationofslowlyaccumulatedNa+bymatureleaveshasbeencalculated.ForBruguieracylindrica,themostextensivelystudiedspecies,60%oft
7、hesaltintheleafisaccumulatedslowlyinthematurephase,thusmorethanduringtheinitialphaseofrapidexpansiongrowth.Thelimiteddatasuggestthatgland-bearingspeciesshowsmallerchangesinmatureleafNa+contentthandogland-lessspecies.Keywords.mangrovematureleafsalinitytolerancesaltdisposalleafdrop
8、22INTRODUCTIONWhenmangrovesgrowinseawate
