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1、www.ylongedu.com新托福TPO22阅读原文(一)：SpartinaTPO22-1：Spartina Spartinaalterniflora,knownascordgrass,isadeciduous,perennialfloweringplantnativetotheAtlanticcoastandtheGulfCoastoftheUnitedStates.Itisthedominantnativespeciesofthelowersaltmarshesalongthesecoast
2、s,whereitgrowsintheintertidalzone(theareacoveredbywatersomepartsofthedayandexposedothers). Thesenaturalsaltmarshesareamongthemostproductivehabitatsinthemarineenvironment.Nutrient-richwaterisbroughttothewetlandsduringeachhightide,makingahighrateoffoodpr
3、oductionpossible.Astheseaweedandmarshgrassleavesdie,bacteriabreakdowntheplantmaterial,andinsects,smallshrimplikeorganisms,fiddlercrabs,andmarshsnailseatthedecayingplanttissue,digestit,andexcretewasteshighinnutrients.Numerousinsectsoccupythemarsh,feeding
4、onlivingordeadcordgrasstissue,andredwingblackbirds,sparrows,rodents,rabbits,anddeerfeeddirectlyonthecordgrass.Eachtidalcyclecarriesplantmaterialintotheoffshorewatertobeusedbythesubtidalorganisms. Spartinaisanexceedinglycompetitiveplant.Itspreadsprimari
5、lybyundergroundstems;coloniesformwhenpiecesoftherootsystemorwholeplantsfloatintoanareaandtakerootorwhenseedsfloatintoasuitableareaandgerminate.Spartinaestablishesitselfonsubstratesrangingfromsandandsilttogravelandcobbleandistolerantofsalinitiesrangingfr
6、omthatofnearfreshwater(0.05percent)tothatofsaltwater(3.5percent).Becausetheylackoxygen,marshsedimentsarehighinsulfidesthataretoxictomostplants.Spartinahastheabilitytotakeupsulfidesandconvertthemtosulfate,aformofsulfurthattheplantcanuse;thisabilitymakesi
7、teasierforthegrasstocolonizemarshenvironments.AnotheradaptiveadvantageisSpartina’sabilitytousecarbondioxidemoreefficientlythanmostotherplants. ThesecharacteristicsmakeSpartinaavaluablecomponentoftheestuarieswhereitoccursnaturally.Theplantfunctionsasast
8、abilizerandasedimenttrapandasawww.ylongedu.comnurseryareaforestuarinefishandshellfish.Onceestablished,astandofSpartinabeginstotrapsediment,changingthesubstrateelevation,andeventuallythestandevolvesintoahighmarshsystemwhereSpartin
