徐托福tpo1-33閱讀原文05翻譯

Researchhasshownthatcertainmineralsarerequiredbyntsfornormalgrowthanddevelopment.Thesoilisthesourceoftheseminerals,whichareabsorbedbythentwiththewaterfromthesoil.Evennitrogen,whichisagasinitselementalstate,isnormallyabsorbedfromthesoilasnitrateions.Somesoilsarenotoriouslydeficientinmicronutrientsandarethereforeunabletosupportmostntlife.So-calledserpentinesoils,forexample,aredeficientincalcium,andonlyntsabletotoleratelowlevelsofthismineralcansurvive.Inmodernagriculture,mineraldepletionofsoilsisamajorconcern,sinceharvestingcropsinterruptstherecyclingofnutrientsbacktothesoil.Mineraldeficienciescanoftenbedetectedbyspecificsymptomssuchaschlorosis(lossofchlorophyllresultinginyelloworwhiteleaftissue),necrosis(isolateddeadpatches),anthocyaninformation(developmentofdeepredpigmentationofleavesorstem),stuntedgrowth,anddevelopmentofwoodytissueinanherbaceousnt.Soilsaremostcommonlydeficientinnitrogenandphosphorus.Nitrogen-deficientntsexhibitmanyofthesyptosjustdescribed.Leavesdevelopchlorosis;stesareshortandslender,andanthocyanindiscolorationoccursonstems,petioles,andlowerleafsurfaces.Phosphorus-deficientntsareoftenstunted,withleavesturningacharacteristicdarkgreen,oftenwiththeaccumulationofanthocyanin.Typically,olderleavesareaffectedfirstasthephosphorusismobilizedtoyounggrowingtissue.IrondeficiencyischaracterizedbychlorosisbetweenveinsinyoungMuchoftheresearchonnutrientdeficienciesisbasedongrowingntshydroponically,thatis,insoillessliquidnutrientsolutions.Thistechniqueallowsresearcherstocreatesolutionsthatselectivelyomitcertainnutrientsandthenobservetheresultingeffectsonthents.Hydroponicshasapplicationsbeyondbasicresearch,sinceitfacilitatesthegrowingofgreenhousevegetablesduringwinter.Aeroponics,atechniqueinwhichntsaresuspendedandtherootsmistedwithanutrientsolution,isanothermethodforgrowingntswithoutsoil.Whilemineraldeficienciescanlimitthegrowthofnts,anoverabundanceofcertainmineralscanbetoxicandcanalsolimitgrowth.Salinesoils,whichhavehighconcentrationsofsodiumchlorideandothersalts,limitntgrowth,andresearchcontinuestofocusondevelosalt-tolerantvarietiesofagriculturalcrops.Researchhasfocusedonthetoxiceffectsofheavymetalssuchaslead,cadmium,mercury,andaluminum;however,evencopperandzinc,whichareessentialelements,can etoxicinhighconcentrations.Althoughmostntscannotsurviveinthesesoils,certainntshavetheabilitytotoleratehighlevelsoftheseScientistshaveknownforsometimethatcertainnts,calledhyperaccumulators,canconcentratemineralsatlevelsahundredfoldorgreaterthannormal.Asurveyofknownhyperaccumulatorsidentifiedthat75percentofthemamassednickel,cobalt,copper,zinc,manganese,lead,andcadmiumareothermineralsofchoice.Hyperaccumulatorsruntheentirerangeofthentworld.Theymaybeherbs,shrubs,ortrees.Manymembersofthemustardfamily,spurgefamily,legumefamily,andgrassfamilyaretophyperaccumulators.Manyarefoundintropicalandsubtropicalareasoftheworld,whereaccumulationofhighconcentrationsofmetalsmayaffordsomeprotectionagainstnt-eatinginsectsandmicrobialpathogens.Onlyrecentlyhaveinvestigatorsconsideredusingthesentstocleanupsoilandwastesitesthathavebeencontaminatedbytoxiclevelsofheavymetals–anenvironmentallyfriendlyapproachknownasphytoremediation.Thisscenariobeginswiththentingofhyperaccumulatingspeciesinthetargetarea,suchasanabandonedmineoranirrigationpondcontaminatedbyrunoff.Toxicmineralswouldfirstbeabsorbedbyrootsbutlaterrelocatedtothestemandleaves.Aharvestoftheshootswouldremovethetoxiccompoundsoffsitetobeburnedorcompostedtorecoverthemetalforindustrialuses.Afterseveralyearsofcultivationandharvest,thesitewouldberestoredatacostmuchlowerthanthepriceofexcavationandreburial,thestandardpracticeforremediationofcontaminatedsoils.Forexamples,infieldtrials,thentalpinepennycressremovedzincandcadmiumfromsoilsnearazincsmelter,andnmustard,nativetoPakistanand,hasbeeneffectiveinreducinglevelsofseleniumsaltsby50percentincontaminatedsoils.

礦物質(zhì)和植物多的礦物質(zhì)。一項(xiàng)對已知富集植物的表明，它們中75%積聚了鎳，而鈷、銅、 基斯坦和的芥菜可以將染土壤中硒的水平有效地降低50%。TheOriginofthePacificIslandThegreaterPacificregion,traditionallycalledOceania,consistsofthreeculturalareas:Melanesia,Micronesia,andPolynesia.Melanesia,inthesouthwestPacific,containsthelargeislandsofNewGuinea,theSolomons,Vanuatu,andNewCaledonia.Micronesia,theareanorthofMelanesia,consistsprimarilyofsmallscatteredislands.PolynesiaisthecentralPacificareainthegreattriangledefinedbyHawaii,EasterIsland,andNewZealand.BeforethearrivalofEuropeans,theislandsinthetwolargestculturalareas,PolynesiaandMicronesia,togethercontainedapopulationestimatedat700,000.SpeculationontheoriginofthesePacificislandersbeganassoonasoutsidersencounteredthem,intheabsenceofsolidlinguistic,archaeological,andbiologicaldata,manyfancifulandmutuallyexclusivetheoriesweredevised.PacificarevariouslythoughttohavecomefromNorthAmerica,SouthAmerica,Egypt,Israel,and,aswellasSoutheastAsia.ManyoldertheoriesimplicitlydeprecatedthenavigationalabilitiesandoverallculturalcreativityofthePacificislanders.Forexample,BritishanthropologistsG.ElliotSmithandW.J.PerryassumedthatonlyEgyptianswouldhavebeenskilledenoughtonavigateandcolonizethePacific.TheyinferredthattheEgyptiansevencrossedthePacifictofoundthegreatcivilizationsoftheNewWorld(NorthandSouthAmerica).In1947NorwegianadventurerThorHeyerdahldriftedonabalsa-lograftwestwardwiththewindsandcurrentsacrossthePacificfromSouthAmericatoprovehistheorythatPacificislanderswereNativeAmericans(alsocalledAmericanns).LaterHeyerdahlsuggestedthatthePacificwaspeopledbythreemigrations:byNativeAmericansfromthePacificNorthwestofNorthAmericadriftingtoHawaii,byPeruviansdriftingtoEasterIsland,andbyMelanesians.In1969hecrossedtheAtlanticinanEgyptian-stylereedboattoproveEgyptianinfluencesintheAmericas.Contrarytothesetheorists,theoverwhelmingevidenceofphysicalanthropology,linguistics,andarchaeologyshowsthatthePacificislanderscamefromSoutheastAsiaandwereskilledenoughasnavigatorstosailagainsttheprevailingwindsandcurrents.ThebasicculturalrequirementsforthesuccessfulcolonizationofthePacificislandsincludetheappropriateboat-building,sailing,andnavigationskillstogettotheislandsinthefirstce,domesticatedntsandgardeningskillssuitedtooftenmarginalconditions,andavariedinventoryoffishingimplementsandtechniques.ItisnowgenerallybelievedthattheseprerequisitesoriginatedwithpeoplesspeakingAustronesianlanguages(agroupofseveralhundredrelatedlanguages)andbegantoemergeinSoutheastAsiabyabout5000B.C.E.Thecultureofthattime,basedonarchaeologyandlinguisticreconstruction,isassumedtohavehadabroadinventoryofcultivatedntsincludingtaro,yarns,banana,sugarcane,breadfruit,coconut,sago,andrice.Justasimportant,theculturealsopossessedthebasicfoundationforaneffectivemaritimeadaptation,includingoutriggercanoesandavarietyoffishingtechniquesthatcouldbeeffectiveforoverseasvoyaging.ContrarytotheargumentsofsomethatmuchofthepacificwassettledbyPolynesiansaccidentallymaroonedafterbeinglostandadrift,itseemsreasonablethatthisfeatwas plishedbydeliberatecolonizationexpeditionsthatsetoutfullystockedwithfoodanddomesticatedntsandanimals.DetailedstudiesofthewindsandcurrentsusingcomputersimulationssuggestthatdriftingcanoeswouldhavebeenamostunlikelymeansofcolonizingthePacific.Theseexpeditionswerelikelydrivenbypopulationgrowthandpoliticaldynamicsonthehomeislands,aswellasthechallengeandexcitementofexploringunknownwaters.BecauseallPolynesians,Micronesians,andmanyMelanesiansspeakAustronesianlanguagesandgrowcropsderivedfromSoutheastAsia,allthesepeoplesmostcertainlyderivedfromthatregionandnottheNewWorldorelsewhere.Theundisputedpre-ColumbianpresenceinOceaniaofthesweetpotato,whichisaNewWorlddomesticate,hassometimesbeenusedtosupportHeyerdahl’s“AmericannsinthePacific”theories.However,thisisonentoutofalonglistofSoutheastAsiandomesticates.AsPatrickKirch,anAmericananthropologist,pointsout,ratherthanbeingbroughtbyraftingSouthAmericans,sweetpotatoesmightjusthaveeasilybeenbroughtbackbyreturningPolynesiannavigatorswhocouldhavereachedthewestcoastofSouthAmerica.

太平洋群島居民的尼西亞和密克羅尼西亞島嶼群一共有差不多70萬人口。對于太平洋群島居民的思索開始于外來者和島民們的接觸，由于缺乏可靠GElliotSmithWJ.Perry認(rèn)為只有埃及人才能熟練地進(jìn)行航海和還有美拉尼西亞人。1969年，他駕駛一條埃及樣式的蘆葦船穿過，證明的語系）5000年前就出現(xiàn)在東南亞。通過考古學(xué)和有時(shí)候被用來證明Heyerdahl的印第安人在太平洋的理論。然而，這是一種在東南亞馴化植物的長之外的植物。正如人類學(xué)家PatrickKirch所TheCambrianThegeologictimescaleismarkedbysignificantgeologicandbiologicalevents,includingtheoriginofEarthabout4.6billionyearsago,theoriginoflifeabout3.5billionyearsago,theoriginofeukaryoticlife-forms(livingthingsthathavecellswithtruenuclei)about1.5billionyearsago,andtheoriginofanimalsabout0.6billionyearsago.ThelasteventmarksthebeginningoftheCambrianperiod.AnimalsoriginatedrelativelylateinthehistoryofEarth—inonlythelast10percentofEarth’shistory.Duringageologicallybrief100-million-yearperiod,allmodernanimalgroups(alongwithotheranimalsthatarenowextinct)evolved.Thisrapidoriginanddiversificationofanimalsisoftenreferredtoas“theCambrianScientistshaveaskedimportantquestionsaboutthisexplosionformorethanacentury.WhydiditoccursolateinthehistoryofEarth?Theoriginofmulticellularformsoflifeseemsarelativelysimplestepcomparedtotheoriginoflifeitself.Whydoesthefossilrecordnottheseriesofevolutionarychangesduringtheevolutionofanimals?Whydidanimallifeevolvesoquickly?Paleontologistscontinuetosearchthefossilrecordforanswerstothesequestions.Oneinterpretationregardingtheabsenceoffossilsduringthis100-million-yearperiodisthatearlyanimalsweresoftbodiedandsimplydidnotfossilize.Fossilizationofsoft-bodiedanimalsislesslikelythanfossilizationofhard-bodiedanimals,butitdoesoccur.Conditionsthatpromotefossilizationofsoft-bodiedanimalsincludeveryrapidcoveringbysedimentsthatcreateanenvironmentthatdiscourages position.Infact,fossilbedscontainingsoft-bodiedanimalshavebeenknownformanyTheEdiacarafossilformation,whichcontainstheoldestknownanimalfossils,consistsexclusivelyofsoft-bodiedforms.AlthoughnamedafterasiteinAustralia,theEdiacaraformationisworldwideindistributionanddatestoPrecambriantimes.This700-million-year-oldformationgivesfewcluestotheoriginsofmodernanimals,however,becausepaleontologistsbelieveitrepresentsanevolutionaryexperimentthatfailed.Itcontainsnoancestorsofmodernanimalgroups.AslightlyyoungerfossilformationcontaininganimalremainsistheTommotianformation,namedafteralocaleinRussia.ItdatestotheveryearlyCambrianperiod,anditalsocontainsonlysoft-bodiedforms.Atonetime,theanimalspresentinthesefossilbedswereassignedtovariousmodernanimalgroups,butmostpaleontologistsnowagreethatallTommotianfossilsrepresentuniquebodyformsthataroseintheearlyCambrianperiodanddisappearedbeforetheendoftheperiod,leavingnodescendantsinmodernanimalgroups.Athirdfossilformationcontainingbothsoft-bodiedandhard-bodiedanimalsprovidesevidenceoftheresultoftheCambrianexplosion.Thisfossilformation,calledtheBurgessShale,isinYohoNationalParkintheCanadianRockyMountainsofBritishColumbia.ShortlyaftertheCambrianexplosion,mudslidesrapidlyburiedthousandsofmarineanimalsunderconditionsthatfavoredfossilization.Thesefossilbedsprovideevidenceofabout32modernanimalgroups,plusabout20otheranimalbodyformsthataresodifferentf