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1、新托福TPO5阅读原文(一):MineralsandPlantsTPO-5-1：MineralsandPlantsResearchhasshownthatcertainmineralsarerequiredbyplantsfornormalgrowthanddevelopment.Thesoilisthesourceoftheseminerals,whichareabsorbedbytheplantwiththewaterfromthesoil.Evennitrogen,whichisagasinitselementalstate,isno
2、rmallyabsorbedfromthesoilasnitrateions.Somesoilsarenotoriouslydeficientinmicronutrientsandarethereforeunabletosupportmostplantlife.So-calledserpentinesoils,forexample,aredeficientincalcium,andonlyplantsabletotoleratelowlevelsofthismineralcansurvive.Inmodernagriculture,mine
3、raldepletionofsoilsisamajorconcern,sinceharvestingcropsinterruptstherecyclingofnutrientsbacktothesoil.Mineraldeficienciescanoftenbedetectedbyspecificsymptomssuchaschlorosis(lossofchlorophyllresultinginyelloworwhiteleaftissue),necrosis(isolateddeadpatches),anthocyaninformat
4、ion(developmentofdeepredpigmentationofleavesorstem),stuntedgrowth,anddevelopmentofwoodytissueinanherbaceousplant.Soilsaremostcommonlydeficientinnitrogenandphosphorus.Nitrogen-deficientplantsexhibitmanyofthesymptomsjustdescribed.Leavesdevelopchlorosis;stemsareshortandslende
5、r,andanthocyanindiscolorationoccursonstems,petioles,andlowerleafsurfaces.Phosphorus-deficientplantsareoftenstunted,withleavesturningacharacteristicdarkgreen,oftenwiththeaccumulationofanthocyanin.Typically,olderleavesareaffectedfirstasthephosphorusismobilizedtoyounggrowingt
6、issue.Irondeficiencyischaracterizedbychlorosisbetweenveinsinyoungleaves.Muchoftheresearchonnutrientdeficienciesisbasedongrowingplantshydroponically,thatis,insoillessliquidnutrientsolutions.Thistechniqueallowsresearcherstocreatesolutionsthatselectivelyomitcertainnutrientsan
7、dthenobservetheresultingeffectsontheplants.Hydroponicshasapplicationsbeyondbasicresearch,sinceitfacilitatesthegrowingofgreenhousevegetablesduringwinter.Aeroponics,atechniqueinwhichplantsaresuspendedandtherootsmistedwithanutrientsolution,isanothermethodforgrowingplantswitho
8、utsoil.Whilemineraldeficienciescanlimitthegrowthofplants,anoverabundanceofcertainminerals
