种子休眠专业外语Presentation

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1、SeedDormancySeeddormancyisaconditionofplantseedsthatpreventsgerminatingunderoptimalenvironmentalconditions.Living,nondormantseedsgerminatewhensoiltemperaturesandmoistureconditionsaresuitedforcellularprocessesanddivision;dormantseedsdonot.Oneimportant

2、functionofmostseedsisdelayedgermination,whichallowstimefordispersalandpreventsgerminationofalltheseedsatsametime.Thestaggeringofgerminationsafeguardssomeseedsandseedlingsfromsufferingdamageordeathfromshortperiodsofbadweatherorfromtransientherbivores;

3、italsoallowssomeseedstogerminatewhencompetitionfromotherplantsforlightandwatermightbelessintense.Anotherformofdelayedseedgerminationisseedquiescence,whichisdifferentthantrueseeddormancyandoccurswhenaseedfailstogerminatebecausetheexternalenvironmental

4、conditionsaretoodryorwarmorcoldforgermination.Manyspeciesofplantshaveseedsthatdelaygerminationformanymonthsoryears,andsomeseedscanremaininthesoilseedbankformorethan50yearsbeforegermination.Someseedshaveaverylongviabilityperiod,andtheoldestdocumentedg

5、erminatingseedwasnearly2000yearsoldbasedonradiocarbondating.OverviewTruedormancyorinnatedormancyiscausedbyconditionswithintheseedthatpreventgerminationundernormallyidealconditions.Oftenseeddormancyisdividedintotwomajorcategoriesbasedonwhatpartofthese

6、edproducesdormancy:exogenousandendogenous.Therearethreetypesofdormancybasedontheirmodeofaction:physical,physiologicalandmorphological.Therehavebeenanumberofclassificationschemesdevelopedtogroupdifferentdormantseeds,butnonehavegaineduniversalusage.Dor

7、mancyoccursbecauseofawiderangeofreasonsthatoftenoverlap,producingconditionsinwhichdefinitivecategorizationisnotclear.Compoundingthisproblemisthatthesameseedthatisdormantforonereasonatagivenpointmaybedormantbecauseofanotherreasonatalaterpoint.Someseed

8、sfluctuatefromperiodsofdormancytonondormancy,anddespitethefactthatadormantseedappearstobestaticorinert,inrealitytheyarestillreceivingandrespondingtoenvironmentalcues.ExogenousdormancyExogenousdormancyiscausedbyconditionsoutsidetheembryoandisoftenbrok