植物营养物质plantnutrition.ppt

Chapter37Lecture Plantnutrition Copyright 2002PearsonEducation Inc publishingasBenjaminCummings SectionA NutritionalRequirementsofPlants 1 Thechemicalcompositionofplantsprovidescluestotheirnutritionalrequirements2 Plantsrequireninemacronutrientsandatleasteightmicronutrients3 Thesymptomsofamineraldeficiencydependonthefunctionandmobilityoftheelement CHAPTER37PLANTNUTRITION Everyorganismisanopensystemconnectedtoitsenvironmentbyacontinuousexchangeofenergyandmaterials Intheenergyflowandchemicalcyclingthatkeepanecosystemalive plantsandotherphotosyntheticautotrophsperformthekeystepoftransforminginorganiccompoundsintoorganicones Atthesametime aplantneedssunlightasitsenergysourceforphotosynthesisandrawmaterials suchasCO2andinorganicions tosynthesizeorganicmolecules Therootandshootsystemsextensivelynetworkaplantwithitsenvironment Introduction Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Earlyideasaboutplantnutritionwerenotentirelycorrectandincluded Aristotle shypothesisthatsoilprovidedthesubstanceforplantgrowthvanHelmont sconclusionfromhisexperimentsthatplantsgrowmainlyfromwaterHale spostulatethatplantsarenourishedmostlybyair Plantsdoextractmineralsfromthesoil 1 Thechemicalcompositionofplantsprovidescluestotheirnutritionalrequirements Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Mineralnutrientsareessentialchemicalelementsabsorbedfromsoilintheformofinorganicions Forexample plantsacquirenitrogenmainlyintheformofnitrateions NO3 Yet asindicatedbyvanHelmont sdata mineralnutrientsfromthesoilmakeonlyasmallcontributiontotheoverallmassofaplant About80 85 ofaherbaceousplantiswater Becausewatercontributesmostofthehydrogenionsandsomeoftheoxygenatomsincorporatedintoorganicatoms onecanconsiderwateranutrienttoo Copyright 2002PearsonEducation Inc publishingasBenjaminCummings However onlyasmallfractionofthewaterenteringaplantcontributestoorganicmolecules Over90 islostbytranspiration Mostofthewaterretainedbyaplantfunctionsasasolvent providesmostofthemassforcellelongation andhelpsmaintaintheformofsofttissuesbykeepingcellsturgid Byweight thebulkoftheorganicmaterialofaplantisderivednotfromwaterorsoilminerals butfromtheCO2assimilatedfromtheatmosphere Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Theuptakeofnutrientsoccursatboththerootsandtheleaves Roots throughmycorrhizaeandroothairs absorbwaterandmineralsfromthesoil Carbondioxidediffusesintoleavesfromthesurroundingairthroughstomata Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 1 Ofthe15 20 ofaherbaceousplantthatisnotwater about95 ofthedryweightisorganicsubstancesandtheremaining5 isinorganicsubstances Mostoftheorganicmaterialiscarbohydrate includingcelluloseincellwalls Thus carbon hydrogen andoxygenarethemostabundantelementsinthedryweightofaplant Becausesomeorganicmoleculescontainnitrogen sulfur andphosphorus theseelementsarealsorelativelyabundantinplants Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Morethan50chemicalelementshavebeenidentifiedamongtheinorganicsubstancespresentinplants However itisunlikelythatallareessential Rootsareabletoabsorbmineralssomewhatselectively enablingtheplanttoaccumulateessentialelementsthatmaybepresentinlowconcentrationsinthesoil However themineralsinaplantreflectthecompositionofthesoilinwhichtheplantisgrowing Therefore someoftheelementsinaplantaremerelypresent whileothersareessential Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Aparticularchemicalelementisconsideredanessentialnutrientifitisrequiredforaplanttogrowfromaseedandcompletethelifecycle Hydroponiccultureshaveidentified17elementsthatareessentialnutrientsinallplantsandafewotherelementsthatareessentialtocertaingroupsofplants 2 Plantsrequireninemacronutrientsandatleasteightmicronutrients Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Hydroponicculturecandeterminewhichmineralelementsareactuallyessentialnutrients Plantsaregrowninsolutionsofvariousmineralsdissolvedinknownconcentrations Iftheabsenceofaparticularmineral suchaspotassium causesaplanttobecomeabnormalinappearancewhencomparedtocontrolsgrowninacompletemineralmedium thenthatelementisessential Fig 37 2 Elementsrequiredbyplantsinrelativelylargequantitiesaremacronutrients Thereareninemacronutrientsinall includingthesixmajoringredientsinorganiccompounds carbon oxygen hydrogen nitrogen sulfur andphosphorus Theotherthreearepotassium calcium andmagnesium Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Elementsthatplantsneedinverysmallamountsaremicronutrients Theeightmicronutrientsareiron chlorine copper zinc manganese molybdenum boron andnickel Mostofthesefunctionascofactorsofenzymaticreactions Forexample ironisametalliccomponentincytochromes proteinsthatfunctionintheelectrontransferchainsofchloroplastsandmitochondria Whiletherequirementforthesemicronutrientsissomodest onlyoneatomofmolybdenumforevery16millionhydrogenatomsindrymaterials adeficiencyofamicronutrientcanweakenorkillaplant Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Thesymptomsofamineraldeficiencydependpartlyonthefunctionofthatnutrientintheplant Forexample amagnesiumdeficiency aningredientofchlorophyll causesyellowingoftheleaves orchlorosis 3 Thesymptomsofamineraldeficiencydependonthefunctionandmobilityoftheelement Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 3 Therelationshipbetweenamineraldeficiencyanditssymptomscanbelessdirect Forexample chlorosiscanalsobecausedbyirondeficiencybecauseironisarequiredcofactorinchlorophyllsynthesis Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Mineraldeficiencysymptomsdependalsoonthemobilityofthenutrientwithintheplant Ifanutrientmovesaboutfreelyfromonepartofaplanttoanother thensymptomsofthedeficiencywillappearfirstinolderorgans Young growingtissueshavemore drawingpower thanoldtissuesfornutrientsinshortsupply Forexample ashortageofmagnesiumwillleadtochlorosisfirstinolderleaves Ifanutrientisrelativelyimmobile thenadeficiencywillaffectyoungpartsoftheplantfirst Oldertissuemayhaveadequatesupplieswhichtheyretainduringperiodsofshortage Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Thesymptomsofamineraldeficiencyareoftendistinctiveenoughforaplantphysiologistorfarmertodiagnoseitscause Thiscanbeconfirmedbyanalyzingthemineralcontentoftheplantandthesoil Deficienciesofnitrogen potassium andphosphorusarethemostcommonproblems Shortagesofmicronutrientsarelesscommonandtendtobegeographicallylocalizedbecauseofdifferencesinsoilcomposition Theamountofmicronutrientneededtocorrectadeficiencyisusuallyquitesmall butanoverdosecanbetoxictoplants Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Onewaytoensureoptimalmineralnutritionistogrowplantshydroponicallyonnutrientsolutionsthatcanbepreciselyregulated Thistechniqueispracticedcommercially buttherequirementsforlaborandequipmentmakeitrelativelyexpensivecomparedwithgrowingcropsinsoil Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 4 Mineraldeficienciesarenotlimitedtoterrestrialecosystems noraretheyuniquetoplantsamongphotosyntheticorganisms Forexample populationsofplanktonicalgaeinthesouthernoceansarerestrainedbydeficienciesofironinseawater InalimitedtrialintherelativelyunproductiveseasbetweenTasmaniaandAntarctica researchersdemonstratedthatdispersingsmallamountsofironproducedlargealgalbloomsthatpulledcarbondioxideoutoftheair Seedingtheoceanswithironmayhelpslowtheincreaseincarbondioxidelevelsintheatmosphere butitmayalsocauseunanticipatedenvironmentaleffects Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Copyright 2002PearsonEducation Inc publishingasBenjaminCummings SectionB TheRoleoftheSoilinPlantNutrition 1 Soilcharacteristicsarekeyenvironmentalfactorsinterrestrialecosystems2 Soilconservationisonesteptowardsustainableagriculture CHAPTER37PLANTNUTRITION Thetextureandchemicalcompositionofsoilaremajorfactorsdeterminingwhatkindsofplantscangrowwellinaparticularlocation Plantsthatgrownaturallyinacertaintypeofsoilareadaptedtoitsmineralcontentandtextureandareabletoabsorbwaterandextractessentialnutrientsfromthatsoil Plants inturn affectthesoil Thesoil plantinterfaceisacriticalcomponentofthechemicalcyclesthatsustainterrestrialecosystems 1 Soilcharacteristicsarekeyenvironmentalfactorsinterrestrialecosystems Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Soilhasitsoriginintheweatheringofsolidrock Waterthatseepsintocrevicesandfreezesinwinterfracturestherock andacidsdissolvedinthewateralsohelpbreakdowntherock Organisms includinglichens fungi bacteria mosses andtherootsofvascularplants acceleratethebreakdownbythesecretionofacidsandastheexpansionoftheirrootsinfissurescracksrocksandpebbles Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Thisactivityeventuallyresultsintopsoil amixtureofrock livingorganisms andhumus aresidueofpartiallydecayedorganicmaterial Topsoilandotherdistinctsoillayers calledhorizons areoftenvisibleinverticalprofile Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 5 Thetextureoftopsoildependsonthesizeofitsparticles whichareclassifiedfromcoarsesandtomicroscopicclayparticles Themostfertilesoilsareusuallyloams madeupofroughlyequalamountsofsand silt particlesofintermediatesize andclay Loamysoilshaveenoughfineparticlestoprovidealargesurfaceareaforretainingmineralsandwater whichadheretotheparticles Loamsalsohaveenoughcourseparticlestoprovideairspacesthatsupplyoxygentotherootforcellularrespiration Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Inadequatedrainagecandramaticallyimpactsurvivalofmanyplants Plantscansuffocateifairspacesarereplacedbywater Rootscanalsobeattackedbymoldsfavoredbythesoakedsoil Someplantsareadaptedtowaterloggedsoil Forexample mangroves thatinhabitswampsandmarshes havesomerootsmodifiedashollowtubesthatgrowupwardandfunctionassnorkels Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Topsoilishometoanastonishingnumberandvarietyoforganisms Ateaspoonofsoilhasabout5billionbacteriathatcohabitwithvariousfungi algaeandotherprotists insects earthworms nematodes andtherootsofplants Theactivitiesoftheseorganismsaffectthephysicalandchemicalpropertiesofthesoil Forexample earthwormsaeratesoilbytheirburrowingandaddmucusthatholdsfineparticlestogether Bacterialmetabolismaltersmineralcompositionofsoil PlantrootsextractwaterandmineralsbutalsoaffectsoilpHandreinforcethesoilagainsterosion Humusisthedecomposingorganicmaterialformedbytheactionofbacteriaandfungiondeadorganisms feces fallenleaves andotherorganicrefuse Humuspreventsclayfrompackingtogetherandbuildsacrumblysoilthatretainswaterbutisstillporousenoughfortheadequateaerationofroots Humusisalsoareservoirofmineralnutrientsthatarereturnedtothesoilbydecomposition Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Afteraheavyrainfall waterdrainsawayfromthelargerspacesofthesoil butsmallerspacesretainwaterbecauseofitsattractionforthesoilparticles whichhaveelectricallychargedsurfaces Somewateradheressotightlytohydrophilicparticlesthatitcannotbeextractedbyplants butsomewaterboundlesstightlytotheparticlescanbeabsorbedbyroots Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 6 Manyminerals especiallythosewithapositivecharge suchaspotassium K calcium Ca2 andmagnesium Mg2 adherebyelectricalattractiontothenegativelychargedsurfacesofclayparticles Clayinsoilpreventstheleachingofmineralnutrientsduringheavyrainorirrigationbecauseofthelargesurfaceareaforbindingminerals Mineralsthatarenegativelycharges suchasnitrate NO3 phosphate H2PO4 andsulfate SO42 areusuallynotboundtightlytosoilparticlesandthustendtoleachawaymorequickly Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Positivelychargedmineralionsaremadeavailabletotheplantwhenhydrogenionsinthesoildisplacethemineralionsfromtheclayparticles Thisprocess calledcationexchange isstimulatedbytherootswhichsecreteH andcompoundsthatformacidsinthesoilsolution Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Ittakescenturiesforasoiltobecomefertilethroughthebreakdownofsoilandtheaccumulationoforganicmaterial However humanmismanagementcandestroysoilfertilitywithinjustafewyears Soilmismanagementhasbeenarecurringprobleminhumanhistory 2 Soilconservationisonesteptowardsustainableagriculture Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Forexample theDustBowlwasanecologicalandhumandisasterthatoccurredinthesouthwesternGreatPlainsoftheUnitedStatesinthe1930s Beforethearrivaloffarmers theregionwascoveredwithhardygrassestheheldthesoilinplaceinspiteoflongrecurrentdroughtsandtorrentialrains Inthe30yearsbeforeWorldWarI homesteadersplantedwheatandraisedcattle whichleftthesoilexposedtowinderosion Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Severalyearsofdroughtresultedinthelossofcentimetersoftopsoilthatwereblownawaybythewinds Millionsofhectaresoffarmlandbecameuseless andhundredsofthousandsofpeoplewereforcedtoabandontheirhomesandland Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 7 Tounderstandsoilconservation wemustbeginwiththepremisethatagricultureisunnatural Innaturalecosystems mineralnutrientsareusuallyrecycledbythedecompositionofdeadorganicmaterial Incontrast whenweharvestacrop essentialelementsaredivertedfromthechemicalcyclesinthatlocation Ingeneral agriculturedepletesmineralsinthesoil Togrowatonofwheat thesoilgivesup18 2kgofnitrogen 3 6kgofphosphorus and4 1kgofpotassium Thefertilityofthesoildiminishesunlessreplacedbyfertilizers andmostcropsrequirefarmorewaterthanthenaturalvegetationforthatarea Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Farmershavebeenusingfertilizerstoimprovecropyieldssinceprehistory Historically thesehaveincludedanimalmanureandfishcarcasses Indevelopednationstoday mostfarmersusecommercialfertilizerscontainingmineralsthatareeitherminedorpreparedbyindustrialprocesses Theseareusuallyenrichedinnitrogen phosphorus andpotassium oftendeficientinfarmandgardensoils Afertilizermarked 10 12 8 is10 nitrogen asammoniumornitrate 12 phosphorus asphosphoricacid and8 potassium asthemineralpotash Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Manure fishmeal andcompostare organic fertilizersbecausetheyareofbiologicaloriginandcontainmaterialintheprocessofdecomposing Theorganicmaterialmustbedecomposedtotheinorganicnutrientsthatrootscanabsorb Intheend themineralsthataplantextractsfromthesoilareinthesameformwhethertheycamefromorganicfertilizerorfromachemicalfactory Compostreleasesnutrientsgradually whilemineralsincommercialfertilizersareavailableimmediately Excessfertilizersareoftenleachedfromthesoilbyrainwaterorirrigationandmaypollutegroundwater streams andlakes Tofertilizejudiciously thesoilpHmustbeappropriatebecausepHaffectscationexchangeandinfluencesthechemicalformofallminerals Eventhoughanessentialelementmaybeabundantinthesoil plantsmaybestarvingforthatelementbecauseitisboundtootightlytoclayorisinachemicalformthattheplantcannotabsorb BecauseachangeinpHmaymakeonemineralmoreavailable butanotherlessavailable adjustmentstopHofsoilistricky ThepHofthesoilmustbematchedtothespecificmineralneedsofthecrop SulfatelowersthepH limingincreasesthepH Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Amajorproblemwithacidsoils particularlyintropicalareas isthataluminumdissolvesinthesoilatlowpHandbecomestoxictoroots Someplantscancopewithhighaluminumlevelsinthesoilbysecretingcertainorganicionsthatbindthealuminumandrenderitharmless Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Evenmorethanmineraldeficiencies theunavailabilityofwatermostoftenlimitsthegrowthofplants Irrigationcantransformadesertintoagarden butfarminginaridregionsisahugedrainonwaterresources Anotherproblemisthatirrigationinanaridregioncangraduallymakethesoilsosaltythatitbecomescompletelyinfertilebecausesaltsintheirrigationwateraccumulateinthesoilasthewaterevaporates Eventually thesaltmakesthewaterpotentialofthesoilsolutionlowerthanthatofrootcells whichthenloosewaterinsteadofabsorbingit Valuabletopsoilislosttowindandwatererosioneachyear Thiscanbereducedbyplantingrowsoftreesbetweenfieldsasawindbreakandterracingahillsidetopreventtopsoilfromwashingaway Somecropssuchasalfalfaandwheatprovidegoodgroundcoverandprotectsoilbetterthancornandothercropsthatareusuallyplantedinrows Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Fig 37 8 Soilisarenewableresourcesinwhichfarmerscangrowfoodforgenerationstocome Thegoalissustainableagriculture acommitmentembracingavarietyoffarmingmethodsthatareconservation minded environmentallysafe andprofitable Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Someareashavebecomeunfitforagricultureorwildlifeastheresultofhumanactivitiesthatcontaminatethesoilorgroundwaterwithtoxicheavymetalsororganicpollutants Inplaceofcostlyanddisruptiveremediationtechnologies suchasremovalandstorageofcontaminatedsoils phytoremediationtakesadvantageoftheremarkableabilitiesofsomeplantspeciestoextractheavymetalsandotherpollutantsfromthesoil Theseareconcentratedintheplanttissuewheretheycanbeharvested Forexample alpinepennycress Thlaspicaerulescens canaccumulatezincinitsshootsatconcentrationsthatare300timesthelevelthatmostplantstolerate Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Copyright 2002PearsonEducation Inc publishingasBenjaminCummings SectionC TheSpecialCaseofNitrogenasaPlantNutrient 1 Themetabolismofsoilbacteriamakesnitrogenavailabletoplants2 Improvingtheproteinyieldofcropsisamajorgoalofagriculturalresearch CHAPTER37PLANTNUTRITION Itisironicthatplantssometimessuffernitrogendeficiencies fortheatmospheresisnearly80 nitrogen PlantscannotusenitrogenintheformofN2 Itmustfirstbeconvertedtoammonium NH4 ornitrate NO3 Intheshortterm themainsourceofnitrogenisthedecompositionofhumusbymicrobes includingammonifyingbacteria 1 Themetabolismofsoilbacteriamakesnitrogenavailabletoplants Copyright 2002PearsonEducation Inc publishingasBenjaminCummings Nitrogenislostfromthislocalcyclewh