第三节植物根系对水分的吸收Absorption of water by third plant roots.docx

第三节植物根系对水分的吸收Absorption of water by third plant roots.docx

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第三节植物根系对水分的吸收Absorptionofwaterbythirdplantroots

第三节植物根系对水分的吸收（Absorptionofwaterbythirdplantroots）

Absorptionofwaterbythirdplantroots

Partofrootwaterabsorption

Two.Thewayofrootwaterabsorption

Three.Themechanismofrootwaterabsorption

Four,theinfluenceofsoilconditionsofwaterabsorption

Characteristicsof1.rootsystem:

Rootsystemisthemainorganofplantabsorbingwater

Partofrootwaterabsorption

Elongationzone

Meristematiczone

Rootcap

Theroothairzone

Rootvolume,roothairnumber

Blackwheatinthebox,andthemeasurementoftheroothairs,atotallengthoftenthousandkilometers,adaylongoutofthenewrootandroothairatotallengthof5kilometers.

Ithasadeeprootandawidedistribution

Therootofwheatissoluble1.5-2m,cornismorethan2m,appletreeis10-12meters.

2.thepositionofrootabsorbingwater

Themainpartofrootabsorptionisatthetipoftheroot,

Theroothairzone

Elongationzone

Meristematiczone

Rootcap

Inthetransplantationofseedlingsshouldbeavoidedwhenrootinjury.

roottip

Thestrongestwaterabsorptioncapacity

Thereasonofthewaterabsorptioncapacityoftheroothairzone:

（1）theroothairzonehasmanyrootabsorptionarea（5~10times）;

（2）theexternalroothairzonecoveredbypectinviscosity,stronghydrophilicity,andisbeneficialtotheadhesionandabsorptionofsoilparticles;

（3）conductingtissueoftheroothairzonedeveloped,theresistancetowatermovement

Inthetransplantationofseedlingsshouldbeavoidedwhenrootinjury.

Two.Thewayofrootwaterabsorption

1.plastidpathway

2.apoplasticpathway

Theradialtransportpathwayfromthesoilthroughroothairs,cortexandendodermis,parenchymacellsintothewatercolumntubetwo:

Itreferstothemovementofwaterfromthecytoplasmofacellthroughplasmodesmatatothecytoplasmofanothercell.Slowermovingspeed.

Plastidpathwayandapoplasticpathwayofrootwaterabsorption

Two.Thewayofrootwaterabsorption

1.plastidpathway

2.apoplasticpathway

Watermovesthroughthecellwall,intercellularspace,etc.withoutprotoplasm,andmovesrapidly.

Theapoplastoftherootisdividedintotwopartsbytheendodermis:

theapoplastoutsidetheendodermisandtheapoplastoutsidetheendodermis

Thestripoftheendothelialcellwall

Waterentersthecellonlythroughtheprotoplasmoftheendodermis.Thatis,enteringtheplastid.Apoplasticspace-endothelialcellprotoplastlayer（plastid）-apoplasticspace（catheter）.

Apoplast

Theendodermis,includingroothairs,cortexcelllayer,cellwallandintercellularspace

Kjeldahlband

Suberification,filmandthewallclosetogether.Waterandsolutecan'tpassthroughfreely.

Internalapoplast

Insidetheendothelium,includingthematureductsandthemiddlecolumn.

Three.Themechanismofrootwaterabsorption

Accordingtothepowerofwaterabsorption,therearetwowaysofplantrootwaterabsorption:

activeabsorptionofwater

passiveabsorptionofwater

Mainmode

（1）rootpressureandactivewaterabsorption

1.rootpressure

Activewaterabsorptionisthewaterabsorptioncausedbythephysiologicalactivityofrootsystem.Itisgenerallybelievedthattherootforceofactivewaterabsorptionisrootpressure.

Rootpressure（rootpressure）-thepressurethatcauseswatertorisefromtherootsbecauseofthephysiologicalactivityofplantroots.

Bleeding

Spitwater

Twophenomenathatconfirmrootpressure:

Ifitiscutofffromthebaseoftheplantneartheground,itisnotlongbeforealiquiddropcomesoutofthewound.Thephenomenonoffluidspillingfrominjuredorbrokenplanttissueiscalledbleeding.Theeffluentwasbleedingsap.

Bleeding

Spitwater

Twophenomenathatconfirmrootpressure:

Thecomponentsofbleedingsapincludewater,inorganicsubstance,organicsubstanceandplanthormone,andthemetabolismoftheheelcanbestudiedaccordingtothebleedingcurrent.

Theamountofbleedingcanberegardedasanindexofphysiologicalactivityofrootsystem.

Bleeding

Spitwater

Twophenomenathatconfirmrootpressure:

Noinjuredplants,suchasinthesoilmoisturesufficient,suitabletemperature,humidenvironment,thetiporedgeofthebladealsohasthephenomenonofliquidsecretion,thisphenomenoniscalledwaterspitting（guttation）.

Spitwater

Themechanismof2.rootpressuregeneration

Maincontent:

Theextracellularsubstanceoutsidetheendodermis,endothelium（corticalcellwall,intercellularspace）andtheapoplast（middlecolumnduct）withintheendodermisformapermeablesystem,

Themetabolicactivityoftherootendodermistoproduceectoplasmbodyandendotheliallayertotheouterbodybetweentheendoplasmicreticulumandthewaterpotentialdifference,smoothwaterpotentialdifferencepenetrationintotherootcatheterthroughtheendotheliallayer.

Penetrationtheory

Howdoestherootcanalandtheouterfluidestablishtheosmoticsystem?

WithfoursuberificationthickenedendotheliallayerontheCasparianstrip,cannotallowfreewaterandnutrientsthrough.

Watercanonlytransportinwardsthroughtheprotoplasmofendothelialcells.

Thewholeendodermiscellislikeaselectivepermeablemembraneseparatingthemiddlecolumnfromthecortex.

Aslongasthereiswaterpotentialdifferencebetweenthewaterinthemiddlecolumnandthewaterinthecortex,thewaterwillpassinandoutthecolumnthroughthepermeation.

Whyisthewaterpotentialinthecatheterlowerthanthatoftheouterfluid?

Thesoluteinthesoilcandiffusewiththewaterthroughtheapoplasttotheroot,andwhenitreachestheendodermis,thediffusionissuppressedbythestrip.

BecauseofthehighconcentrationofO2inthecortex,itispossibletoproduceenoughstrongrespirationandgenerateenoughenergytofacilitatetheactiveabsorptionofions.Throughtheactivetransport,theionsaretransportedtotheparenchymacellsofthestelethroughtheplasmodesmata.

Theionsinthemiddlecolumndiffusetotheapoplast（especiallytheduct）alongtheconcentrationgradient,whichincreasestheionconcentrationinthecatheteranddecreasesthewaterpotential.

Thiscreatesawaterpotentialgradientacrosstheendodermis,wherewaterentersthecolumnthroughosmosistoproducerootpressure.

Throughmetabolism

Experimentalphenomenasupportingpermeationtheory:

Whentheplantrootsareplacedinpurewater,thebleedingvelocityisaccelerated;

Ifyouplantrootsinconcentratedsolution,thewoundflowisreduced,andthebleedingsapisevensuckedback;

Thus,theformationofrootpressureisaosmoticprocess,andisrelatedtothemetabolismofplants.

Activewaterabsorptionisusuallynottherootsystem'sactiveabsorptionofwateritself

Buttheplantactiveabsorbsolutebymetabolicenergy,resultinginthecatheterthewatersolutionislowerthantheoutsidethewatersolution,thewaterispassivelyalongthewaterpotentialgradientfromtheoutsideintothecatheter,realpowerflowisthewaterpotentialdifference.

（two）transpirationtensionandpassivewaterabsorption

1.passivewaterabsorption

Thewayofabsorbingwaterthroughtranspirationforceiscalledpassivewaterabsorption.

2.transpirationpull（transpirationalpull）

Becausetranspirationproducesaseriesofwaterpotentialgradients,theforcethatcauseswatertoriseinthetubeiscalledtranspirationpull.

Theproportionofactivewaterabsorptionandpassivewaterabsorptionintheprocessofplantwaterabsorptionvarieswithplantgrowthandtranspirationrate.Usuallytranspirationofplants,especiallytalltrees,themainwaytoabsorbwaterispassivewaterabsorption.Activewaterabsorptionisthemainmodeofwaterabsorptiononlywhentheleavesarenotexpandedorfalleninthespring,andatnightwhenthetranspirationrateisverylow.

Activewaterabsorptionandpassivewaterabsorption

Four.Conditionsaffectingrootwaterabsorption

Thefactorsthataffectthesoilwaterpotentialandrootwaterpotentialaffecttherootabsorptionofwater.

（1）soilmoisturestatus

Soilmoisturecanbedividedintothreeparts:

1.gravitywater

2.hygroscopicwater（orboundwater）

3.capillarywater

Theamountofavailablewaterinthesoildirectlyaffectsthewaterabsorptionoftherootsystem

Fieldwaterholdingcapacity

Excludingallgravitywater,retainingallcapillarywaterandhygroscopicwater,thepercentageofsoilmoistureandsoildryweightiscalledfieldcapacity.Usuallyaround20%.

Maximumwaterholdingcapacity

Saturatedwaterholdingcapacity.Watercontentwhenallthevoidsinthesoilarefilledwithwater.Usuallyaround40%.

Whenthesoilwatercontentisabout70%ofthefieldwatercapacity,thesoilfertilityisgood.

Temporarywilting（temporarywilting）

Permanentwilting（permanentwilting）

Permanentwiltingcoefficient（permanentwiltingcoefficient）:

thepercentageofsoilmoistureandsoildryweightwhenplantsarepermanentlywilting.

Itisrelatedtosoilparticlesize,soilcolloidnumber,cropspeciesandsoon.Coarsesand,finesand,loamandclayincreasesuccessively.

Wilt

（two）soiltemperature

Lowtemperaturecanreducethewaterabsorptionrateofrootsystem

Soiltemperatureistoohighforrootwaterabsorptionisalsounfavorable.

（three）soilaerationstatus

Inthewellventilatedsoil,thewaterabsorptioncapacityofrootsystemisstronger.

Soilaerationnotonlycauseswaterabsorptionobstruction,butalsocausesrootpoisoningdeathforalongtime.

Becauseofpoorsoilaeration,O2contentdecreased,CO2concentrationincreased,theshorttermcanmaketheeffectofrootrespirationdecreased,rootpressure,thuspreventingwater;alongtime,itwillca