Tolerance mechanisms of three potted ornamental plants grown under moderate salinity

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ContentslistsavailableatScienceDirect

Scientia

Horticulturae

j o u r n a l ho me p ag e :w w w . e l s e v i e r . c o m / l o c a t e / s c i h o r t i

Tolerance

mechanisms

of

three

potted

ornamental

plants

grown

under

moderate

salinity

Pedro

García-Caparrós

a

_,

_Alfonso

_Llanderal

a

_,

_Maribela

_Pestana

b

_,

_Pedro

_José

_Correia

b

_,

María

Teresa

Lao

a,∗

a_Higher_Polytechnic_School_and_Experimental_Science_College,_Department_of_Agronomy_of_the_University_of_Almeria,_Agrifood_Campus_of_{International}

ExcellenceceiA3.Ctra.Sacramentos/n,LaCa˜nadadeSanUrbano,04120Almería,Spain

b_Universidade_do_Algarve,_MeditBio,_FCT,_Edifício_8,_Campus_de_Gambelas,_8005-139_Faro,_Portugal

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received27October2015

Receivedinrevisedform14January2016 Accepted20January2016

Availableonline4February2016 Keywords: Biomass Electricalconductivity Mineralcomposition Proline Salttolerance Sugars

a

b

s

t

r

a

c

t

ThescarcityofwaterintheMediterraneanareahasfrequentlyledtotheuseofsalinewaterinorder toirrigateornamentalplantsinmanynurseries.However,beforethelarge-scaleuseofsuchwaters,the waysinwhichtheplantsdealwiththesalinityneedtobeevaluated.PlantsofAloeveraL.Burm,Kalanchoe blossfeldianaPoellnandGazaniasplendensLemsp.weregrowninpotswithamixtureofsphagnum peat-mossandPerlite.Inordertoevaluatetheeffectsofdifferentlevelsofsalinity,threetreatmentsusing differentNaClconcentrations(Electricalconductivity=2.0(control),4.5and7.5dSm−1)wereapplied overaperiodof60days.Attheendoftheexperiment,thegrowth,physiologicalparametersandmineral contentoftherootsandleaveswereassessedforeachsalinitytreatment.After60daysofexposureto salinity,thetotalbiomassofallspeciesdecreasedsimilarly.Themineralcompositionofrootsandleaves wasclearlyaffected.Osmolytes,suchasproline,playedanimportantroleintheosmoticadjustmentin allspeciesincreasingintherootsandleavesatthehigherECi.Differentmechanismsofthesalttolerance

weretriggeredineachspecies.AveraplantsshowedNa+_accumulation_at_the_root_level_and_a_decrease

insucculenceindexofleaves.K.blossfeldianaplantsshedleavestoreleaseNa+_and_G._splendens_plants

accumulatedCl−andNa+_at_the_root_level,_secreted_salt_from_leaves,_lost_salt_by_shedding_of_old_leaves

andincreasedthesucculenceindexofremainingleaves.Weconcludedthattheuseofsalinewatersis feasibleforgrowingtheseornamentalplants,andG.splendensseemstobeparticularlywelladaptedto salinity,aconsiderationthatisparticularlyrelevantinaridsalineareas.

1. Introduction

Theworldwideproductionvalueofornamentalpottedplants

andcutﬂowersisabout50billionD,correspondingtoanestimated

globalconsumptionofbetween100and150billionD(Lütkenetal.,

2012).However,nowadaysthereisadecreaseinproductionaround

Abbreviations:ANOVA,analysisofvariance;DW,dryweight;ECi,electrical

con-ductivityoftheirrigationwater;FW,freshweight;H2O2,hydrogenperoxide;HPLC,

highperformanceliquidcromatography;LWR,leafweightratio;LSD,least signif-icantdifference;L,leaves;PAR,photosyntheticallyactiveradiation;RH,relative humidity;RWR,relativerootweightratio;Yr,relativeyield;R,roots;SI, succu-lenceindex;H2SO4,sulphuricacid;TDW,totaldryweight;TSS,totalsolublesugars;

UL,unwashedleaves;WL,washedleaves;WCl,watercontentinleaves;WCr,water

contentinroots;Y,yield. ∗ Correspondingauthor.

E-mailaddresses:pedrogar123@hotmail.com(P.García-Caparrós),

mtlao@ual.es,mtlaoa@yahoo.es(M.T.Lao).

theworldpartlyduetosoilandwatersalinization(Cassanitietal.,

2013)ashappensinthesouth-easterncoastalregionofSpainwith

highsalinity levelsin thewater due tothe overexploitationof

groundwaterandseawaterintrusioninsomeaquifers(Consejería

deMedioAmbienteyOrdenacióndelTerritorio(CMAOT),2012).

Therearethreemajorconstraintsforplantgrowthundersaline

conditions:(1)thewaterstress,arisingfromlowerwaterpotential

ofthegrowingmedium,(2)iontoxicityassociatedwiththe

exces-siveuptakemainlyofClandNa,and(3)anutrientimbalancecaused

bydepression in theuptake of othernutrient ions(Marschner,

1995).Tocopewiththeeffectsofsaltstress,plantshaveevolved

manybiochemicalandmolecularmechanismstoreduce

detrimen-taleffectsofionsfromthosepartsoftheplantswheretheymaybe

harmful;thesemechanismsincludeaccumulationattherootlevel,

thesheddingofdryleaves,saltsecretionandsucculence(Aslam

etal.,2011).Thecellosmoticadjustmentnecessaryforgrowthin

salineenvironmentsmaybeaccomplishedbytheaccumulationof

inorganicandorganicsolutes.Theinorganicionsarebelievedto

http://dx.doi.org/10.1016/j.scienta.2016.01.031

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besequesteredinthevacuoles,whiletheorganicsolutessuchas

sugarsand prolinemaybecompartmentalized inthecytoplasm

tobalancethelowosmoticpotentialinthevacuole(Munnsand

Tester,2008).

Duetothegreateconomicimportanceoftheproductionof

pot-tedplantsinsouth-easterncoastofSpainintherecentyears,and

thechallengestothecontinuedsupplyofnon-salinewater

men-tionedabove,furtherinvestigationisnecessaryontheeffectsof

differentirrigationwatersalinity(electricalconductivity,ECi)in

horticulturalspecies.Theadjustmentofthenutrientsolutionin

termsofelectricalconductivity(EC)iscrucialfortheoptimization

ofthewaterandnutrientavailability(KangandIersel,2004).

Weinvestigatedthreespecies.AloeveraL.Burm,amemberof

theAsphodelaceaefamily,isasucculentplantwithgreenleaves,

widelycultivatedandvaluedduetoitsshortgrowthperiodandthe

higheconomicvalue(Moghbelietal.,2012).Kalanchoeblossfeldiana

Poelln,originatingfromMadagascar,isamemberofCrassulaceae

(Abdel-Raouf,2012)anditisoneofthemostﬁnancially

impor-tantﬂowering,pottedplantspeciesinEurope,withaproductionof

morethan150millionplantsperyear(Mibusetal.,2014).Gazania

splendensLemasp.,withinCompositae,tribeArctotideae,subtribe

Gorteriinae(Karis,2007),isanornamentalshrubwidelycultivated

ingardensacrosstheworld,beingendemicfromsouthernAfrica

(Mageeetal.,2011).Nevertheless,veryfewstudiesontheeffects

ofdifferentECoftheirrigationwateronthenutritionand

phys-iologyhavebeenreportedforK.blossfeldiana(Taybietal.,1995;

Mariauxetal.,1997)andG.splendens.InthecaseofA.vera,there

aremanyinvestigationsontheeffectsofhighNaClconcentration

suchas100and200mMNaCl(Xuetal.,2006;Zhengetal.,2009)

or100%seawater(Liuetal.,2007),butverylittleisknown

regard-ingtheeffectsunderlowNaClstress.Therefore,inthistrial,apot

experimentwithA.vera,K.blossfeldianaandG.splendensplantswas

establishedinordertodeterminetheeffectsofdifferentsalinity

levelsoftheirrigationwaterontheplants’drymassandallocation,

mineralnutrientcontent,mechanismsofsalttoleranceandtheir

physiologicalchanges.Suchinformationcanbeusedfor

optimiz-ingthecropmanagementwithsalinewatersandalsoforevaluating

whichofthesespeciesmightbesuitablefortheuseofsalinewaters.

2. Materialandmethods

2.1. Plantmaterialandexperimentalconditions

ThepresentstudywascarriedoutattheUniversityof

Alme-ria(36◦49N,2◦24W).Rootedcuttings(plants)ofA.veraL.Burm,

K.blossfeldianaPoellnandG.splendensLemwereobtainedfrom

alocalnurseryandtransplantedinto1.5Lpolyethylenepots

con-tainingamixtureofsphagnumpeat-mossandPerlite80:20(v/v).

Duringthetrial(60days),thepotswereplacedinagreenhouseof

150m2_._The_{microclimatic}_conditions_inside_the_greenhouse_for_the

experimentalperiod,monitoredcontinuouslywithHOBOSHUTTLE

sensors(modelH08-004-02)showedadailyaveragetemperature

of25.4±2.5◦C,relativehumidity(RH)of65.6±2.1%and

photosyn-theticallyactiveradiation(PAR)of225±9.4␮molm−2s−1.

2.2. Experimentaldesignandtreatments

Thisexperimenthadbeenperformedpreviouslywithawider

rangeofsalinities.Theexperimentconsistedofthreetreatments

usingdifferentsalinitiesinastandardsolutionwiththefollowing

composition(inmmolL−1):0.70H2PO4−,6.00NO3−,2.00SO42−,

3.00K+_,_2.00_Ca2+_and_1.40_Mg2+_amended_with_different

concen-trationsofNaCl(solesalinizingagent)toachieveEClevelsofthe

irrigationwater(ECi)ofeither2.0(T1orcontrol,3mmolL−1NaCl),

4.5(T2,30mmolL−1NaCl)or7.5(T3,60mmolL−1 NaCl)dSm−1.

Theplantswereirrigatedmanuallyeveryday.TheECiandpHwere

measureddailyusingaconductivitymeterandpHmeters(models

MilwaukeeC66andpH52),respectively.Thetreatments(EC

lev-els)werechoseninaccordancewithpreviousresearchreportedby

WuandDodge(2005)regardingthesalinitytolerancewitharange

from2toover6dSm−1toavoidsaltstresssymptoms,considering

theirrigationwiththenutrientsolutionof2.0dSm−1asacontrol

intheexperiment.Thevolumeofsalinewateraddedtoeachpot

duringtheexperimentalgrowingperiodwas4.2Lforeachsaline

treatmentandthesameforallspecies.Theexperimentaldesign

consistedofthreesalinitytreatments,fourblocks,andfourplants

(oneplantperpot)perblockgivingatotalof12plantsperspecies

plusborderplants.

2.3. Plantparameters

Attheendofthesalineperiod,theplantswereharvestedandthe

substrategentlywashedfromtherootsoffourplantspertreatment

forallthestudiedspecies.Theplantsweredividedintoroots(R)

andleaves(L) andtherespectivefreshweights(FW)measured;

rootsandleaveswerethenoven-driedat60◦Cuntiltheyreached

aconstant weighttomeasuretherespectivedryweights(DW).

Thesedryweightswereusedtocalculateseveralplantparameters

asindicatedbyRyserandLambers(1995)andCorreiaetal.(2010):

theleafweightratio(LWR;leafDWperunitplantDW)andthe

relativerootweightratio(RWR;rootDWperunitplantDW).The

totaldryweight(TDW)wascalculatedasthesumofleavesand

rootsDW.Thefreshanddryweightofrootsandleaveswereused

tocalculatethewatercontent(WC)(−)asindicatedbyBenAmor

etal.(2005):

WC=(FW−DW)

FW (1)

2.4. Yieldresponsesalinitymodels

TomodeltheyieldresponsetothedifferentECivaluesinthe

threespecies,regressionanalysesweretestedandthebestﬁtted

modelswereselectedbasedonthedeterminationcoefﬁcient(R2₎

inaccordancewithSteppuhnetal.(2005)andCorreiaetal.(2010).

Inthisexperiment,thetotalplantDW(rootsandleaves)wasused

asyield(Y),beingassessed60daysfromsalinization.Theabsolute

yield(Y)wasconvertedintorelativeyield(Yr)byemployinga

scal-ingdivisor(Ym)basedonthemaximumvalueoftotalplantbiomass

(DW)obtainedincontrolplants(MaasandHoffman,1977).TheYr

valueforeach salttreatmentwasdeterminedattheend ofthe

experimentaccordingtothefollowingequation:

Yr= _YmY (2)

2.5. Physiologicalmeasurements

Fourplantspertreatmentwererandomlyselectedattheendof

theexperimentineachspeciestodeterminetheNaandCl

accu-mulationbyroots,calculatedastheratiobetweenthequantityof

ClandNaintheroot(R)relativetototalquantityintheplant(Cl−

andNa+_extraction_per_plant_in_mmol/root_DW_in_gram);_(ii)_the

Cl−andNa+_secretion_by_leaves_(L)_was_assessed_by_the_difference

betweenthecontentofthiselementsinwashedleaves(WL)and

inunwashedleaves(UL)(mmolg−1DW);(iii)thelossofNaandCl

wasevaluatedbycollectingandquantifyingthecontentsofthese

elements(mmolg−1DW)inshedoldleaves,and(iv)thesucculence

index(SI)ofleaveswasdeterminedastheratiobetweenleafFW

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Fig.1.Relationshipbetweentherelativeyield(Yr:expressedasTDW)andtheECiinA.vera(A),K.blossfeldiana(B)andG.splendens(C)plantsattheendoftheexperiment.

2.6. Analysisofmineralelements

Theoven-driedsamplesweregroundinamillanddividedin

twosubsamples.Theanalysisofmineralelementsoftherootsand

leaveswasdeterminedinonesubsamplefollowingwater

extrac-tionbyHPLC(HighPerformanceLiquidChromatography;model

Metrohm883BasicICPlus).Thesolubleionicforms(NO3−andCl−)

werequantiﬁedusingacolumnmodelMetrosepASUPP4(IC

con-ductivitydetectorrange0–15000␮Scm−1)asdescribedbyCsáky

andMartínez-Grau(1998).Themobilephasewaspreparedby

mix-ing190.6mgofCO32−and142.8mgofHCO3−andthendilutingin

1Lofdeionizedwater,acidifywithH2SO4(50mM).Theother

sub-samplewasmineralizedwithsulphuricacid(H2SO4,96%)inthe

presenceofhydrogenperoxide(H2O2,P-free)at300◦Candused

forthedeterminationoforganicN,totalP,K+ _and _Na+

concen-tration.TodeterminetheorganicNconcentration(Krom,1980),

1mLofreagentA(8.5gofsodiumsalicylateand0.06gofsodium

nitroprussidein100mLofdeionizedwater)and1mLofreagent

B(4gofsodichydroxidand0.625gofsodicdicloroisocinuratein

100mLofdeionizedwater)wereaddedto0.1mLofmineralized,

shakingafterwards.Passed45min,theabsorbanceat630nmwas

quantiﬁedcolorimetrically(modelShimadzuUV-1201)

compar-ingwithastandardcurveof(NH4)2SO4.Forthedeterminationof

totalP(Hogueetal.,1970),thephosphorusreagentwasprepared

asfollows:10gofammoniummolybdateand5gofammonium

vanadatewereaddedto800mLofboilingdeionizedwater.Then,

thesolutionwascoolediniceand4mLofnitricacidwereadded

dropbydrop.Afterwards,134mLofnitricacidweretransferred

byburette,dilutingwithdeionizedwatertothemarkina1L

vol-umetricﬂaskandmixing.Finally,0.5mLofmineralized,1.5mLof

deionizedwaterand3mLofphosphorusreagentwereadded,

mix-ingandallowingtostandfor1hafterwards.Theabsorbancewas

quantiﬁedcolorimetricallyat430nm(modelShimadzuUV-1201)

usingacalibrationcurvepreparedwithK2HPO4standardsolution.

ThetotalNwascalculatedasthesumoftheorganicNandNO3−

concentration.ThetotalK+_and_Na+_{concentrations}_were_directly

measuredinthemineralizedbyﬂamespectrophotometry(model

JenwayPFP7)(Lachicaetal.,1973).

2.7. Organicsolutesdeterminations

Todeterminetheconcentrationsof prolineandtotal soluble

sugars(TSS)in therootsand leaves,fourplants wererandomly

selectedper treatment in each species at harvest. Fresh

mate-rial (0.5g for each type of organ) wascrushed in 5mL of 95%

(v/v)ethanolandcentrifuged(modelDigicen21R)at3500×gfor

10min.Thepelletwaswashedtwicewith5mLof70%(v/v)ethanol

andrecentrifuged.ThefreeprolineandTSSconcentrationswere

determinedinthealcoholicextractsupernatant.Thefreeproline

concentrationwasdeterminedbytheninhydrinreagentmethod.

Avolumeof2.5mLofninhydrinreagent(25gofninhydrinmixed

with400mLofphosphoricacid6Mand600mLof60%(v/v)glacial

aceticacidshakenat75◦C)plus4mLofdistilledwaterand2.5mL

ofglacialaceticacidwereaddedto2mLofalcoholicextract

super-natant,shakenandheatedinaboilingwater-bathfor45min.The

reactionwasstoppedbyplacingthetesttubesinanicebath.Then

5mLofbenzenewereaddedtothesamples,beingvigorouslymixed

inavortexshakerfor1minafterwards.Aftertheextractionwith

benzene,thefreeprolineconcentrationwasquantiﬁed

colorimetri-callyat515nmusingL-proline(SigmaChemicals)asstandard.Free

prolineconcentrationwasexpressedas␮molg−1FW.Thetotal

sol-ublesugarsconcentrationwasdeterminedbytheanthronereagent

method.FourmLofanthronereagent(300mgofanthronemixed

with300mLof70%(v/v)sulphuricacid)wasaddedto100␮Lof

alcoholicextractsupernatantandthenthemixturewasshaken,

heatedinaboilingwater-bathfor10minandcooledat4◦C.Lastly,

thetotalsolublesugarsconcentrationwasquantiﬁed

colorimetri-callyat650nmusingglucose(SigmaChemicals)asstandard.The

totalsolublesugarsconcentrationwasexpressedas␮molglucose

g−1FW(Irigoyenetal.,1992).

2.8. Statisticalanalysis

The experiment had a completely randomizedblock design,

and thevalues obtainedfor each plantand each variablewere

consideredasindependentreplicates.Eachspecieswasanalysed

independently.Thedatawereanalysedthroughone-way

analy-sisofvariance(ANOVA)andleastsigniﬁcantdifference(LSD)tests

(P<0.05)in ordertoassess thedifferencesbetweentreatments

usingStatgraphicPlusforWindows(version5.1.).

3. Results

3.1. Plantparameters

Throughouttheexperiment,therewerenomortalitiesinany

ofthespeciesinresponsetosalinitytreatments(Table1).

Salin-itydecreasedthetotaldryweight(TDW)inallthespecies(root

dryweight(RDW)wasunaffectedbyECiwhereasleafdryweight

(LDW) decreased signiﬁcantly bysalinity).The leafweigh ratio

(LWR)wasnotaffectedduetosalinitybutthevaluesofrelativeroot

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Fig.2. EffectofECi(2.0,4.5and7.5dSm−1)onchloride(A)andsodium(B)accumulationinroots(Cl−andNa+extractionperplantinmmol/rootDWing)ofA.vera(A),K.

blossfeldiana(K)andG.splendens(G)attheendoftheexperiment.Valuesarethemeans±standarddeviation(errorbars)offourplantspertreatment.Meanswithoutthe sameletterinbarsaresigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest).

Table1

EffectofECi(2.0,4.5and7.5dSm−1)onleaf(LDW),root(RDW)andtotalplantdryweight(TDW)(expressedingram),leafweightratio(LWR),relativerootweightratio(RWR),

watercontentinleaves(WCl)androots(WCr)inA.vera(A),K.blossfeldiana(K)andG.splendens(G)plantsattheendoftheexperiment.Valuesarethemeans±standard

deviationoffourplantspertreatment.MeanswithinacolumnwithinaspecieswithoutthesameletteraresigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest).

ECi(dSm−1) RDW LDW TDW LWR RWR WCl WCr A 2.0 7.73±0.63a 54.27±3.34a 64.50±4.34a 0.82±0.05a 0.10±0.02c 0.96±0.01a 0.87±0.02a 4.5 8.39±1.02a 44.33±3.17b 55.21±2.59b 0.80±0.08a 0.14±0.02b 0.95±0.01a 0.87±0.01a 7.5 7.99±1.14a 35.69±3.41c 45.68±3.19c 0.82±0.04a 0.18±0.01a 0.95±0.01a 0.85±0.01a K 2.0 1.64±0.11a 7.51±0.62a 9.15±0.64a 0.82±0.01a 0.14±0.01c 0.94±0.01a 0.86±0.02a 4.5 1.48±0.29a 6.06±0.42b 7.53±0.31b 0.80±0.09a 0.18±0.02b 0.94±0.01a 0.87±0.01a 7.5 1.33±0.37a 5.19±0.39c 6.90±0.19c 0.80±0.09a 0.23±0.01a 0.92±0.03a 0.87±0.01a G 2.0 2.49±0.47a 22.72±0.80a 25.01±0.38a 0.87±0.05a 0.09±0.02c 0.80±0.02a 0.86±0.01a 4.5 2.74±0.51a 17.99±0.87b 20.93±0.41b 0.86±0.02a 0.14±0.01b 0.83±0.02a 0.86±0.01a 7.5 2.83±0.43a 14.46±0.45c 17.29±0.29c 0.85±0.04a 0.17±0.01a 0.84±0.03a 0.86±0.02a

plantsinallthespeciesattheendoftheexperiment.Thewater

con-tent(WC)wasunaffectedbyECiirrespectiveoftheanalysedorgan

(rootsorleaves)inallspecies.

3.2. Yieldresponsesalinitymodels

Therelativeyield(Yr)wasrelatedtotheelectricalconductivity

ofirrigationwater(ECi)inallspeciesattheendoftheexperiment

throughthebestmodelswiththelargestR2 _value,_the_Yr_being

inverselyproportionaltotheECi(Fig.1).

3.3. Physiologicalmeasurements

UnderdifferentECi,theCl−andNa+rootaccumulationwas

dif-ferentbetweenthespecies(Fig.2).TheA.veraplantsremainedwith

nosigniﬁcantdifferencesonCl−accumulationbetweenthesaline

treatments,whereastheNa+_accumulation_increased_{signiﬁcantly}

athigherECicomparingtothecontrolattheendofthe

experi-ment.Contrastingly,theK.blossfeldianaplantsirrigatedwith4.5

and7.5dSm−1decreasedtheCl−accumulationwithrespecttothe

control,whilenosigniﬁcanteffectfortheNa+_accumulation_was

found60daysfromsalinizationforallthetreatments.InG.

splen-densplants,theCl−andNa+_accumulation_at_4.5_and_7.5_dS_m−1

weregreaterthanthoseforthecontroltreatment(2.0dSm−1).

TheleavesofA.veraandK.blossfeldianadidnotsecreteCl−and

Na+_whereas_in_the_G._splendens_plants,_the_Cl−_and_Na+_secretion_by

theleavesincreasedwithincreasingsalinitytreatments(Table2).

TheeffectsofdifferentECionCl−andNa+concentrationinthe

shedleavesweredifferentinallthespeciesattheendofthe

exper-iment(Fig.3).A.veradidnotshedleavesinanytreatment.

InshedleavesofK.blossfeldiana,Cl−concentrationwassimilar

betweentreatments, while Na+ _{concentration}_increased

signiﬁ-cantlywithrespecttothecontroltreatment.G.splendensshowed

aclearincreaseofCl−andNa+_{concentrations}_in_the_shed_leaves_at

greaterECi(4.5and7.5dSm−1)attheendofthesalineperiod.K.

blossfeldianalost1.5–3.0%ofleavesDWinrelationtoTDW,whereas

G.splendensshedsleavesinapercentagefrom15to21%ofTDW

(datanotshown).

Theplantsshoweddifferenttrendsinleafsucculenceindex(SI)

(Fig.4).InK.blossfeldianaplants,SIremainedunchangedacrossthe

treatments.TheSIofA.veraplantsdecreasedsigniﬁcantlyat4.5

and7.5dSm−1comparedwiththecontroltreatment(2.0dSm−1),

whereasinG.splendens,SIincreasedsigniﬁcantlyathigherECi.

3.4. Ionconcentrationsintissues

Themineralcompositionoftherootsandleavesofallthespecies

wasaffectedbythesalinitytreatments(Table3).InA.veraplants,

leafNdecreasedwithhigherECi,whiletherewasnoclearresponse

intheroots.TherootPwassimilarinalltreatments,whereasinthe

leavesoftheplantsirrigatedwith4.5dSm−1showedthegreatest

concentration.TheKconcentrationintherootsandleavesofthe

plantsirrigatedwithhigherECi(4.5and7.5dSm−1)werelower

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Table2

EffectofECi(2.0,4.5and7.5dSm−1)onCl(A)andNa(B)inwashedleaves(WL)andinunwashedleaves(UL).DW:dryweight.Foreachtreatment,Cl−andNa+concentration

inWLandULinthesamecolumnwiththesamelettersarenotsigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest).Foreachtreatment,thedifferencebetweenULandWL inthesamerowwiththesamelettersarenotsigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest).Dataarethemeans±standarddeviationoffourplantspertreatment.

Species Elementconcentration(mmolg−1_DW) _EC_i_(dS_m−1₎

2.0 4.5 7.5 A Cl− _WL _1.36_±_0.03_a _1.38_±_0.02_a _1.36_±_0.01_a UL 1.40±0.03a 1.40±0.01a 1.38±0.02a Cl− _(UL-WL) _0.03_±_0.01_a _0.03_±_0.01_a _0.02_±_0.01_a Na+ _WL _0.81_±_0.05_a _1.24_±_0.03_a _1.49_±_0.05_a UL 0.83±0.03a 1.23±0.05a 1.50±0.04a Na+ _(UL-WL) _0.01_±_0.001_a _0.01_±_0.001_a _0.01_±_0.001_a K Cl− _WL _1.31_±_0.06_a _1.45_±_0.02_a _1.46_±_0.03_a UL 1.35±0.04a 1.49±0.03a 1.49±0.04a Cl− _(UL-WL) _0.03_±_0.01_a _0.04_±_0.01_a _0.03_±_0.01_a Na+ _WL _0.30_±_0.01_a _0.74_±_0.01_a _0.67_±_0.01_a UL 0.31±0.01a 0.75±0.01a 0.69±0.02a Na+ _(UL-WL) _0.01_±_0.001_a _0.01_±_0.001_a _0.01_±_0.002_a G Cl− WL 1.43±0.02b 2.51±0.04b 2.67±0.04b UL 1.62±0.04a 2.73±0.04a 2.98±0.05a Cl− _(UL-WL) _0.18_±_0.01_c _0.21_±_0.01_b _0.26_±_0.01_a Na+ _WL _1.19_±_0.02_b _3.68_±_0.08_b _4.05_±_0.09_b UL 1.46±0.05a 4.01±0.06a 4.53±0.08a Na+ _(UL-WL) _0.27_±_0.01_c _0.34_±_0.01_b _0.46_±_0.02_a

Fig.3.EffectofECi(2.0,4.5and7.5dSm−1)onchloride(A)andsodium(B)concentrationintheshedleavesinA.vera(A)K.blossfeldiana(K)andG.splendens(G)plantsatthe

endoftheexperiment.Valuesarethemeans±standarddeviation(errorbars)offourplantspertreatment.Meanswithoutthesameletterinbarsaresigniﬁcantlydifferent atP<0.05(ANOVAandLSDtest).

Table3

Mineralcomposition(expressedinmmolg−1_DW)_in_roots_(R)_and_leaves_(L)_of_A._vera_(A),_K._{blossfeldiana}_(K)_and_G._splendens_(G)_at_the_end_of_the_experiment._Values_are

themeans±standarddeviationoffourplantspertreatment.MeanswithinacolumnwithoutthesameletteraresigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest). ECi (dSm−1₎ N P K L R L R L R A 2.0 2.02±0.16a 1.27±0.15a 0.06±0.01b 0.10±0.01a 1.15±0.03a 0.44±0.01a 4.5 0.84±0.23b 0.81±0.08b 0.09±0.01a 0.11±0.01a 1.09±0.01b 0.37±0.03b 7.5 1.08±0.16b 1.28±0.08a 0.03±0.01c 0.11±0.01a 1.01±0.03c 0.32±0.01b K 2.0 1.18±0.08b 1.11±0.09ab 0.08±0.01a 0.05±0.01b 0.97±0.01a 0.48±0.02a 4.5 1.49±0.11a 1.31±0.11a 0.08±0.01a 0.07±0.01a 0.94±0.04a 0.31±0.04b 7.5 1.43±0.16a 1.02±0.09b 0.07±0.01a 0.03±0.01c 0.96±0.03a 0.25±0.03b G 2.0 2.03±0.10a 2.26±0.07a 0.12±0.01a 0.10±0.02b 1.30±0.03a 0.47±0.04a 4.5 1.49±0.07b 1.20±0.04c 0.12±0.01a 0.25±0.01a 1.19±0.04b 0.48±0.04a 7.5 1.87±0.10a 1.60±0.07b 0.04±0.01b 0.10±0.01b 1.11±0.02c 0.45±0.03a

IncontrolplantsofK.blossfeldiana,theleafNlevelwaslower

thanintheothersalttreatments,whilsttherootNshowedthe

highestconcentrationat4.5dSm−1.TheleafPwasnotaffectedby

thesalttreatments,whileintherootsPwashighestintheplants

subjectedto4.5dSm−1.TheleafKwassimilarinalltreatments,

whereasthehighestvalueintherootswasobservedinthecontrol

plants(2.0dSm−1).

InG.splendensplants,leafNwaslowestat4.5dSm−1,whilein

therootsthecontrolplantsshowedthehighestconcentration.The

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Fig.4. EffectofECi(2.0,4.5and7.5dSm−1)onsucculenceindex(SI)inleavesofA.

vera(A),K.blossfeldiana(K)andG.splendens(G)attheendoftheexperiment.Values arethemeans±standarddeviation(errorbars)offourplantspertreatment.Means withoutthesameletterinbarswiththesamecolouraresigniﬁcantlydifferentat P<0.05(ANOVAandLSDtest).

intheroots,thehighestconcentrationwasobservedat4.5dSm−1.

TheleafKdecreasedsigniﬁcantlywiththeECiincrease,whilstin

therootsitremainedconstantinalltreatments.

3.5. Biochemicalanalysis

InA.veraplants,thesugarconcentrationintherootswashigher

thanintheleaves.Theleafsugarincreasedsigniﬁcantlywiththe

highestECi(7.5dSm−1),whileintherootthehighestconcentration

wasfoundinplantsgrownin4.5dSm−1 (Table4).Intheplants

treatedwith4.5and7.5dSm−1,theprolineconcentrationinthe

rootsandleaveswerehigherthaninthecontrolplants.

InK.blossfeldianaplants,thesugarconcentrationintheroots

waslowerthanin theleaves. Salinityledtoareduction ofthe

sugar concentration in the leaves, whereas in the roots sugar

remainedunchanged.Theprolineconcentrationintherootsand

leavesincreasedwiththeECiandthehighestvalueswereobserved

at7.5dSm−1.

InG.splendensplants,thesugarconcentrationintherootswas

higherthanintheleaves.Inthecontrolplants (2.0dSm−1),the

leafsugarconcentrationwashigherthanintheothertreatments,

while the sugar concentration in the roots showed no

differ-encesbetweentreatments.Theleafandrootprolineconcentration

increasedwiththehigherECi.

4. Discussion

Theirrigationwatersalinityhaddifferenteffectsonthebiomass

and biochemical parameters according to the species. Under

increasingECi,theproportionofbiomassallocatedtoleaves(LWR)

wasnotaffectedinanyofthethreespeciestested,thereby

allow-ingtheproductionof marketableplants withmoderatesalinity.

Thesame resultswerealsoobservedin A. veraplants irrigated

withdilutedseawater(Jiangetal.,2014),whileLWRincreasedin

otherpottedplantsasAsteriscusmaritimus(Rodríguezetal.,2005)

irrigatedwith140mMNaClandCistusalbidusandC.

monspelien-sis(Torrecillasetal.,2003)irrigatedwith70and 140mMNaCl.

After60daysofexposure,theincreaseinRWRinthethreespecies

weinvestigatedsuggeststhatthesepottedplantsalteredthe

pat-ternofdrymatterdistributionfavouringrootgrowthovershoot

growthasreportedbyCordovillaetal.(2014)inThymusvulgaris.

Incontrast,Jiangetal.(2014)reporteda decreasein RWRinA.

veraplants.ChangesinTDWwasattributedtoLDWand notto

RDW.Inourexperiment,watercontentwasnotaffectedby

salin-ity.TheseresultsdisagreeingwithJinetal.(2007)andZhengetal.

(2009)whoreportedadecreaseinwatercontentinthedifferent

organsofA.veraplantsassessedwith60%seawaterand200mM

NaCl(highersalinitytreatments),respectively;andwiththedata

obtainedbyNiuandRodríguez(2006)inotherornamental

pot-tedplantsasPenstemoneatonii,Delospermacooperi andGazania

rigensirrigatedathigherEClevels(12dSm−1)whichalsoshowed

adeclineinthewatercontentintherootsandleaves.These

appar-entlycontradictoryresultsmaybeexplainedbythelowerECilevels

imposedinourstreatments.Althoughsomedifferencesdidoccur

inleavesbiomass,theywerenotexpressedinthewatercontent

of thetissues. It is alsopossiblethat ifthe experiment had be

extendedforalongerperiod(>60days)watercontentwillprobably

beaffected.

SalineconditionsinducesanincreaseinCl−andNa+

concen-trationsintherootsandleavesinornamentalpottedspeciesas

reportedby Cassanitiet al. (2009).Under theseconditions, the

tolerancetosalinityineachspeciesistriggeredthroughdifferent

strategiessuchasionsaccumulationatrootlevel,sheddingofdry

leaves,saltsecretionandsucculenceinthedifferentorgans(Aslam

etal.,2011).Inourexperiment,A.veraplantswereableto

accu-mulateonlyNa+_in_roots_while_G._splendens_accumulated_Cl−_and

Na+_which_agrees_very_well_with_the_conclusion_reported_by_Sykes

(1993)explainingthattheabilitybetweenspeciestoaccumulate

Cl− ionsintheroots isindependentofitsability toaccumulate

Na+_ions;_a _good_Cl− _ion_excluder_is_not_necessarily _a_good_Na+

excluder,andviceversa.Thesheddingoftheoldleaveswithhigh

amountsofNaandCl,asamechanismtoovercomethesalinity

proposedbyKoyroetal.(2011)wasonlyperformedinK.

bloss-feldianaandG.splendensplants eventhoughthesheddingleda

slightreductioninTDWandthereforealowerqualityofsaleable

plants.

A.veraandK.blossfeldianaarecharacterizedbythelackofsalt

glands whereas G. splendens hassalt glands. A histoanatomical

studyofleavesinK.blossfeldiana(S¸ipos¸andBunta,2011)reported

thelackoftrichomeswhichexplainstheabsenceofsaltontheleaf

surfaceandtheabsenceofanydifferencesinthelossofCl−and

Na+_by_leaves_in_this_species_observed_in_our_experiment._Wu_et_al.

(2001)alsodidnotﬁndsaltsecretioninotherornamentalpotted

plantsasCeanothussp.andNandinadomestica,treatedwith

salin-ity,presumablybecauseoftheabsenceofglandsontheleafsurface.

Furthermore,inthecaseofG.splendens,themechanismofNaand

Clexcretionbyleavesthroughtrichomesisalsoobservedinother

plantswelladaptedtosalinity,suchasAtriplexsp.(Wahid,2003).

Saltstressaltersthesucculenceoftheleaveswhichis

consis-tentwithavacuolarcompartmentationofions.Inourexperiment,

eachspeciesshowedadifferentpatternunderincreasingNaCl

con-centration. Thedecrease of succulencein A. veraplants can be

interpretedasamechanismofsoluteconcentrationinthecellsap

thuscontributingtotheosmoticadjustment(Matohetal.,1988).

Incontrast,itispossiblethatG.splendenshadpromotedagreater

uptakeofwaterinordertodilutetheexcessofsalts(Munnsetal.,

1983)thusleadingtoahigherSIinleaves.InthecaseofK.

blossfel-dianaplants,thesucculenceindexwasnotaffectedandthiscanbe

duetothelowerlevelsofsalinityappliedtopromotethesucculence

inthisplant.

Theexcessiveaccumulationofsaltsmaycauseachangeonthe

uptakeofmineralnutrientsaswellasinducephytotoxicity(Hu

andSchmidhalter,2005).ThepresentresultsshowedthattheN

andPconcentrationsintherootsandleavesinallthespeciesdid

notshowaclearresponsetosalinity,whereastheK

concentra-tiontendedtoremainwithoutchangesortodecreasewiththesalt

stress:K.blossfeldianawasthebestspeciesmaintainingits

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Table4

Osmolyteconcentration(totalsolublesugars(TSS)andproline)expressedin␮molg−1_FW_in_roots_(R)_and_leaves_(L)_of_A._vera_(A),_K._{blossfeldiana}_(K)_and_G._splendens

(G)plantstreatedoveraperiodof60dayswithdifferentelectricalconductivityoftheirrigationwater(ECi).Valuesarethemeans±standarddeviationoffourplantsper

treatment.MeanswithinarowwithoutthesameletteraresigniﬁcantlydifferentatP<0.05(ANOVAandLSDtest). ECi(dSm−1) 2.0 4.5 7.5 A TSS L 17.11±0.28b 16.44±0.94b 35.11±4.38a R 97.22±16.39ab 115.11±10.88a 74.39±14.78b Proline L 0.09±0.01c 0.19±0.03b 0.29±0.03a R 0.13±0.01c 0.16±0.01b 0.28±0.03a K TSS L 19.33±0.77a 11.28±0.89b 12.06±0.72b R 9.17±1.00a 8.67±0.88a 9.83±0.61a Proline L 0.75±0.10c 1.15±0.11b 1.58±0.17a R 0.63±0.04c 0.77±0.08b 1.55±0.16a G TSS L 27.50±0.78a 18.83±1.17b 18.67±1.00b R 48.72±2.61a 50.33±0.83a 50.94±2.33a Proline L 2.56±0.19c 3.35±0.16b 3.82±0.17a R 1.51±0.50c 2.47±0.30b 4.93±0.39a

literature.SeveralstudiesreportedthatthereductionoftheN

con-centrationattributedtotheCl−andNO3−antagonism(Abdelgadir

etal.,2005),whereasothersreportedanincreasemainlydueto

theaccumulationofN-containingcompounds,suchasaminoacids

includingprolineinresponsetosaltstress(Paridaetal.,2002).On

theotherhand,thePconcentrationinplantscanshowdifferent

trendsundersalinity.Someresearchersfoundadeclinedueto

com-petitionbetweenCl−andH2PO4−(Kayaetal.,2001),whileothers

reportedariseduetotheenergy(ATP)requiredtotransportthe

excessofionsintothevacuoles(MengelandKirkby,2001).The

decreaseofK+_{concentration}_in_organs_of_salinized_plants_in_our

experimentindicatestheexistenceofcompetitioneffectsbetween

Na+_and_K+_ions_which_most_likely_share_the_same_transport

sys-tem(Blumwald,2000;TesterandDavenport,2003;ParidaandDas,

2005).Inaccordance,Cassanitietal.(2009)reportedadecreaseon

K+_{concentration}_in_other_ornamental_potted_plants_as_{Bougainvillea}

glabra,GrevilleajuniperinaandLeptospermumscopariumsubjected

tosalinity.

Osmoticadjustmentinplantscanbeperformedthrough

accu-mulation of osmolytes which are compatible with the cells

metabolism(Hasegawaetal.,2000).Inourexperiment,thechanges

inrootsandleavesinsugarconcentrationsdidnotshowadeﬁned

patterninresponsetodifferentNaClconcentrations,exceptforthe

decreaseinleavesofK.blossfeldianaandG.splendens.Conversely

withtheseresults,otherresearchersreportedanincreaseofsugar

concentrationinrootsandleavesundersaltstressinother

orna-mentalplantsasMelissaofﬁcinalis(KhalidandCai,2011).Onthe

otherhand,fromtheresultsofthis experiment, prolineis

con-ﬁrmedtobeagoodstressindexforsalinityinallthespeciesdue

totheincrement togetherwiththeincrease inNaCl

concentra-tion.Theprolineconcentrationincreaseintherootandleafinall

speciesundersalinitymaybetheresultofadecreaseinthe

pro-linedegradation(Hareetal.,1999)orofanincreaseintheproline

biosynthesis(Luttset al.,1999).In accordancewithourresults,

Murillo-Amadoretal.(2014)reportedanincreaseoftheproline

concentrationintheleavesofA.veraplantsandotherresearchers

alsonotedthisincreaseinotherornamentalpottedplantsas

Ger-berajamesoniiL.(Donetal.,2010)andDelonixregia(Pateletal.,

2009)subjectedtothesaltstress.

Finally,theresultsforbiomassproduction,expressedasTDW

whichisoneofthebasicrequisitesforthenurseryindustry,showed

asimilardecreaseabout30%inallthespeciesundersalinty.These

valuesarefarfromtheacceptablepercentageofdecrease(45%)

pro-posedbylocalornamentalgrowerstoproducemarketableplants,

thereforetheuseofmoderateECilevelsasstudiedinourtrialare

feasibleforthecultivationoftheseornamentalspeciesina

con-trolledenvironment.

5. Conclusions

Salinitytriggereddifferentresponsesineachspecies.Attheend

ofthesalineperiod,allspeciesshowedasimilardecreaseonthe

totalbiomassandthemineralcontentsintherootsandleaveswere

clearlyaffected.Highersalinityledtoanincrease intheproline

concentration,whichmaybeproposedasasalinitystress

indica-tor,whereasthesugarconcentrationdidnotshowacleartrend.

Thedifferentmechanismofsalttoleranceevolvedineachspecie

were:(1)A.veraplantsaccumulatedNa+_at_root_level_and_decreased

thesucculenceinleaves, (2)K.blossfeldianaplantsavoided Na+

accumulationbysheddingleavesand(3)G.splendensplants

trig-geredCl−andNa+_accumulation_at_root_level,_salt_secretion_through

leaves,sheddingofoldleavesandsucculenceincreaseinleaves.

Theseresultssuggesttheimportanceofstudyingthesaltresponse

ofornamentalpottedplantstohelpthegrowersandgardenersto

selectthespecieswhicharemoretoleranttosaltstress.G.splendens

seemstobethemosttolerantbecauseevolvedmoremechanisms

ofsalttolerancewiththesamereductioninthebiomassthanthe

othersspeciesstudied.

Acknowledgment

TheauthorsthankProfessorTimothyFlowersforhissuggestions

andEnglishstylecorrections.

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