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1、www.ylongedu.com新托福TPO5阅读原文(一):MineralsandPlantsTPO-5-1：MineralsandPlants Researchhasshownthatcertainmineralsarerequiredbyplantsfornormalgrowthanddevelopment.Thesoilisthesourceoftheseminerals,whichareabsorbedbytheplantwiththewaterfromthesoil.Evennitrogen,whichisagasinitselementalstate,i
2、snormallyabsorbedfromthesoilasnitrateions.Somesoilsarenotoriouslydeficientinmicronutrientsandarethereforeunabletosupportmostplantlife.So-calledserpentinesoils,forexample,aredeficientincalcium,andonlyplantsabletotoleratelowlevelsofthismineralcansurvive.Inmodernagriculture,mineraldepletion
3、ofsoilsisamajorconcern,sinceharvestingcropsinterruptstherecyclingofnutrientsbacktothesoil. Mineraldeficienciescanoftenbedetectedbyspecificsymptomssuchaschlorosis(lossofchlorophyllresultinginyelloworwhiteleaftissue),necrosis(isolateddeadpatches),anthocyaninformation(developmentofdeepredp
4、igmentationofleavesorstem),stuntedgrowth,anddevelopmentofwoodytissueinanherbaceousplant.Soilsaremostcommonlydeficientinnitrogenandphosphorus.Nitrogen-deficientplantsexhibitmanyofthesymptomsjustdescribed.Leavesdevelopchlorosis;stemsareshortandslender,andanthocyanindiscolorationoccursonste
5、ms,petioles,andlowerleafsurfaces.Phosphorus-deficientplantsareoftenstunted,withleavesturningacharacteristicdarkgreen,oftenwiththeaccumulationofanthocyanin.Typically,olderleavesareaffectedfirstasthephosphorusismobilizedtoyounggrowingtissue.Irondeficiencyischaracterizedbychlorosisbetweenve
6、insinyoungleaves. Muchoftheresearchonnutrientdeficienciesisbasedongrowingplantshydroponically,thatis,insoillessliquidnutrientsolutions.Thistechniqueallowsresearcherstocreatesolutionsthatselectivelyomitcertainnutrientsandthenobservetheresultingeffectsontheplants.Hydroponicshasapplication
7、sbeyondbasicresearch,sinceitfacilitatesthegrowingofgreenhousevegetablesduringwinter.Aeroponics,atechniqueinwhichplantsaresuspendedandtherootsmistedwithanutrientsolution,isanothermethodforgrowingplantswithoutsoil. Whilemineraldeficienciescanlimitthegrowthofplants,anoverab
