Biomass, anatomical changes and osmotic potential in Atriplex nummularia Lindl. cultivated in sodic saline soil under water stress

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ContentslistsavailableatSciVerseScienceDirect

Environmental

and

Experimental

Botany

j o u r n al hom ep age :w w w . e l s e v i e r . c o m / l o c a t e / e n v e x p b o t

Biomass,

anatomical

changes

and

osmotic

potential

in

Atriplex

nummularia

Lindl.

cultivated

in

sodic

saline

soil

under

water

stress

Edivan

Rodrigues

de

Souza

a,∗

_,

_Maria

_Betânia

_Galvão

_dos

_Santos

_Freire

a

_,

Karina

Patrícia

Vieira

da

Cunha

b

_,

_Clístenes

_Williams

_Araújo

_do

_Nascimento

a

_,

Hugo

Alberto

Ruiz

c

_,

_Cíntia

_Maria

_Teixeira

_Lins

a

a_Rural_Federal_University_of_Pernambuco_–_UFRPE,_Agronomy_Department,_Rua_Dom_Manoel_de_Medeiros,_s/n,_Dois_Irmãos._CEP:_52171-900,_Recife,_PE,_Brazil

b_Civil_Engineering_Department,_Federal_University_of_Rio_Grande_do_Norte,_Av._Senador_Salgado_Filho,₃₀₀₀_–_Campus_{Universitário}_Lagoa_Nova._CEP:_59072-970,_Natal,_RN,_Brazil c_Federal_University_of_Espírito_Santo,_Centro_de_Ciências_Agrárias,_Alto_{Universitário.}_CEP:_29500-000,_Alegre,_ES,_Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received9March2012 Accepted14March2012 Keywords: Halophyte Salt-affectedsoil Vesiculartrichome Semi-arid NortheastBrazil

a

b

s

t

r

a

c

t

Atriplexnummulariaexhibitsexcellentadaptabilitytoenvironmentswithhighsalinityandlowwater availability.Accordingly,manystudieshavebeenconductedtoidentifythetoleranceoftheplant.We cultivatedAtriplexinsodicsalinesoilunderconditionsofwaterstressinNortheastBrazil.Thepurposeof thestudywastoevaluatethegrowthcharacteristicsandproductionofleaves,stemsandrootsofAtriplex undertheseconditionsinordertoidentifyanatomicalchangesinvesicularcellsinleafepidermisaswell astoassesstheosmoticpotentialofthesoilsolutionandtheleaves.Theexperimentwasperformedin agreenhousewhereAtriplexwascultivatedfor134daysinpotswithsodicsalinesoil.Thetreatments comprisedfourmoisturelevels(35%,55%,75%and95%ofﬁeldcapacity–FC).Theheight,diameterand drymassofleaf,stemandrootexhibitedtheirhighestvaluesatlevelsofsoilmoisturethatwere75% and95%ofFC.Thehighyieldsofdrybiomassindicatethepotentialuseofthishalophyteforrestoration ofsalt-affectedsoils.Thevesicularcellswereinﬂuencedbythesoilmoisture.Theosmoticpotentialcan serveasagoodindexforevaluatingplantresponsestowaterstressandsalinity.

1. Introduction

Salt-affected soilsare foundin over 100countries. In many

of these regions, salinization is caused by irrigation water

(Rengasamy,2006;Glennetal.,2009).AccordingtotheFAO(2000),

thetotal area of salt-affected soilsin the worldis 831million

hectares.Thistotal includes397millionhectaresof salinesoils

and 434 million hectares of sodic soils. In Brazil, salt-affected

soilsaremostcommonintheNortheast.Effortsarerequiredto

amelioratethesesoils,especiallythroughtheestablishmentof

veg-etation(Qadiretal.,2007,2008;Glennetal.,2009).Tosupportthis

approach,itiscrucialtoevaluatetheperformanceofplantsadapted

tosuchharshconditions.

AccordingtoFlowers&Colmer(2008),halophytesare

charac-terizedasplantsthatcansurviveandreproduceinenvironments

where the salt concentration exceeds 200mmolL−1 of NaCl

(∼20dSm−1).These species constituteapproximately1% ofthe

world’sﬂora. Amongthehalophytes, AtriplexnummulariaLindl.

∗ Correspondingauthor.Tel.:+558133206225;fax:+558133206220. E-mailaddresses:[email protected],[email protected](E.R.deSouza),

[email protected](K.P.V.daCunha),[email protected](H.A.Ruiz).

representsaspeciesofgreatimportance,owingtoitsadaptability

tosalinityand waterdeﬁciency. Hence,studieshavebeen

con-ductedmainlyonitstolerancetosoilsalinity.Accordingly,inview

oftheplant’sadaptationstoaridandsemi-aridenvironments,it

isalsonecessarytoevaluateitsperformanceandtoleranceinthe

presenceoflowwatercontentinthesoil.

Tolerance tosalinity is a complex feature that involvesthe

interactionofseveralproperties.Interesthasgrowninthe

mor-phologicalandanatomicalbehaviorofsalt-tolerantplantsandin

conductingstudiesdesigned toidentifythemechanismsof

tol-erance (Boughalleb et al., 2009). In general, papers investigate

Atriplexgrowthparametersasaffectedbysalinitylevelsonsoil

solutionalthoughsoilhumidityisfundamentaltoassessthegrowth

patternofthisspecies.Thusresearchisalsoneededtoelucidatethe

characteristicsofgrowthpatternsandwaterconsumptionin

halo-phytes(Jordanetal.,2009),especiallyunderconditionsofsalinity

andirrigation.

Planttolerancetowaterstressand salinityrequires an

inte-gratedseriesofchangesinvolvingcellularandmetabolicsystems.

In A.nummularia Lindl., tolerancetosalinityis oftenattributed

tothepresenceofvesiculartrichomesthatcovertheleafsurface.

Thesestructuresshowahighcapacityforsaltaccumulation.Among

thefunctionsattributedtothesetrichomesarewaterabsorption

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E.R.deSouzaetal./EnvironmentalandExperimentalBotany82 (2012) 20–27 21

fromtheatmosphere,waterstorageandsaltsecretion(Mozafar&

Goodin,1970).Evaluationofthepropertiesofthesetrichomesmay

helptoelucidatemechanismsfortolerancetodrynessandsalinity

inA.nummulariaLindl.

Inresponse towater andsalt stress,someplantspecies use

osmoticadjustmenttowithstandseveredehydrationandsustain

importantbiologicalprocesses.Osmoticpotentialcanbeachieved

throughtheaccumulationofsugars,organicacids,aminoacidsand

inorganicionssuchasNa+_,_K+ _and _Cl− ₍_Munns_&_Tester,_2008;

Flowers&Colmer,2008).Oneofthemethodsfortrackingthe

accu-mulationoforganicandinorganicsolutesisthemeasurementof

theosmoticpotential.Osmometersare commonlyusedfor this

purpose.

Theobjectivesofthisstudyweretoevaluatethegrowthand

theproductionofdrymassofleaves,stemsandrootsandtostudy

anatomicalchangesinthevesiculartrichomesoftheleafepidermis

ofA.nummulariaLindl.grownonsalinesodicsoilunderwaterstress

conditions.Thestudyalsoanalyzedtheosmoticpotentialinthe

soilandintheplanttoevaluatethepossibleuseofthisindexfor

assessingsalineenvironments.

2. Materialsandmethods

2.1. Experimentalset-up

Theexperimentwasconductedinagreenhouseandusedasoil

samplecollectedunderﬁeldconditionsat0–30cmdepthina

salt-saturatedareaintheNortheastBrazilianmunicipalityofPesqueira

intheStateofPernambuco(Fig.1).

Thestudyusedpolyethylenepots24cminheight,withadrysoil

capacityof20kg.Thesoilwasair-dried,loosened,homogenized

andsievedthrougha4mmmeshtoﬁllthepots.Forphysicaland

chemicalanalyses,subsamplesweresievedthrougha2mmmesh

(Tables1and2).

Asoilsamplewascollectedfromeachpotafterﬁlling.These

sampleswereusedtocharacterizethechemicalattributesofthe

soil.Theresultsofthischaracterizationwerelatercomparedwith

theresultsofasecondsoilsamplecollectedattheendofthe

exper-iment(Souzaetal.,2011).

2.2. ObtainingseedlingsofAtriplexandapplyingthetreatments

Thestudyused120-day-oldseedlingsofA.nummulariaLindl.

Theplantsweremultipliedusingcuttingsfromasinglemother

planttodecreasethegeneticvariabilityoftheseedlings.

Thesoilmoistureatﬁeldcapacity(0.152gg−1)wasusedasa

ref-erencevalue(Table1).Fourlevelsofhumiditywerethendeﬁned:

35%,55%,75%and95%oftheﬁeldcapacity.Acontroltreatment

withoutAtriplexplantswasmaintainedat95%ofﬁeldcapacity.The

treatmentswereirrigatedeverydaylateintheafternoon,whenall

thepotswereweighedandsuppliedwithenoughwaterto

main-tainthedesiredhumiditylevels.Thewaterusedforirrigationwas

preparedinthelaboratoryusingNaCl,CaCl2andMgCl2atan

elec-tricalconductivity(EC)of750␮Scm−1.ThereferencevalueofEC

usedinthisstudywastheaveragevalueofECfoundinwaterways,

especiallywells,nearthesitefromwhichthesoilforthestudywas

collected.

2.3. Conductingtheexperiment

Whentheseedlingsreached32cminheight,theywere

trans-planted to potsand monitored for 134 days. The plant height

andstemdiameterweremeasuredat6,33,66,96and132days

aftertransplanting(DAT).At134DAT,theshootswerecollected

at1cmfromthesoilsurface,fractionatedintoleavesandstems

andweighedtoobtainthefreshweightofeachplantfraction.All

fractions(leaf,stemandroot)wereplacedinanovenwithforced

circulationat65◦Cuntiltheyreachedweightstabilizationtoobtain

drymassformeasurementandsubsequentanalysis.

2.4. Mineralcompositionofplantparts

Thedrymassobtainedfromtheleaf,stemandrootfractionswas

groundinaWilleygrinder.Nitropercloricdigestion(Silva,2009)

wasthenconducted.Thevaluesofthesodiumandpotassium

con-tentweredeterminedbyﬂameemissionphotometry.Thevaluesof

thecalciumandmagnesiumcontentweredeterminedusing

ICP-OES.Chloridewasdeterminedbyextractioninwaterandtitration

withsilvernitrate.

2.5. Evaluationofvesiculartrichomes

Samplesofmatureleaveswerecollectedandimmediatelyﬁxed

inFAA50solutionforaminimumof24–48h(Johansen,1940)to

determinetheabsolutetrichomedensity(numberoftrichomesper

unitarea),externaldiameterofthestalkcells,externaldiameterof

thevesicularcellsandvesicularvolume.Sampleswerewashedin

distilledwaterandsubsequentlyimmersedinasolutionofsodium

hypochlorite at 10%. Theywere then washed again in distilled

water,separatedfromtheepidermis, stainedwithtwodropsof

1%methyleneblueandmountedin50%glycerol.Theimagesofthe

separatedepidermiswerecapturedbyadigitalcameracoupledto

anopticalmicroscopeandthenanalyzedusingImageToolsoftware.

2.6. OsmoticpotentialinsoilsolutionandleafsapofA.

nummulariaLindl.

Todeterminethetotalosmolalityofleaftissue,leaveswere

col-lectedfromthemiddleportionoftheplantcanopyandmacerated

inamortarwithapestle.Thesapobtainedfromthetissuewas

ﬁlteredandcentrifugedat10,000gfor10minat4◦C(Silvaetal.,

2009).A50␮Laliquotofsupernatantwasusedtodeterminethe

tissueosmolalityusingamicro-osmometer(␮OsmetteTM_Model

5004AutomaticOsmometer).Thevaluesobtainedinmillimolesper

kilogramweretransformedtoosmoticpotentialbytheVan’tHoff

equation(Kirkham,2004;Hillel,2007).Thesameprocedurewas

usedforthesoilsolutionextractedfromthesaturatedsubstrate.

Table1

Physicalcharacteristicsofthesoil(n=36samples).

Bd (kgdm−3₎ Pd (kgdm−3₎ Sand Silt (gkg−1₎ Clay (gkg−1₎ WDC (gkg−1₎ DI (gkg−1₎ FI (gkg−1₎ Tension(atm) Total (gkg−1₎ Coarse (gkg−1₎ Fine (gkg−1₎ 0.1(gg−1₎ _0.33_(g_g−1₎ ₁₅_(g_g−1₎ 1.40 2.67 590 229 361 330 80 60 0.75 0.25 0.21 0.15 0.05

Bd:soilbulkdensity(volumetricringmethod);Pd:soilparticledensity(volumetricﬂaskmethod);WDC:waterdispersedclay;DI:dispersionindex;FI:ﬂocculationindex. DI:WDC/Clay;FI:(1−DI);atm:atmosphere

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Fig.1. MapofBrazil,PernambucoState,andPesqueiramunicipality.

Table2

Chemicalcharacteristicsofthesoil(n=36samples).

Changecomplex Saturationextract Relations(solubles)

Variables Values Variables Values Variables Values

pH(2.5:1) 8.66 ECse(dSm−1) 42.56 Na/Ca 28.39 Ca2+_(cmol ckg−1) 4.73 pHes 7.45 Na/Mg 19.81 Mg2+_(cmol ckg−1) 2.12 Ca2+(mmolcL−1) 16.07 Na/K 122.30 Na+_(cmol ckg−1) 3.31 Mg2+(mmolcL−1) 22.98 Na/Cl 1.11

K+_(cmol_c_kg−1₎ _0.36 _Na+_(mmol_c_L−1₎ _456.19 _Cl/Na _0.90

SB(cmolckg−1) 10.52 K+(mmolcL−1) 3.73 Cl/Ca 25.55

ESP(%) 31.46 Cl−_(mmol_c_L−1₎ _410.64 _Cl/Mg _17.87

TOC(dagkg−1₎ _0.55 _SAR_(mmol_c_L−1₎0.5 _103.21 _Cl/K _110.09

OP(atm) 7.87

SB:sumofbases;ESP:exchangeablesodiumpercentage;TOC:totalorganiccarbon(Yeomans&Bremner,1988);SAR:sodiumadsorptionratio;OP:osmoticpotential. Methods:pH(2.5:1)(Silva,2009);Exchangeablecations(Thomas,1982);Solublecations(Richards,1954).

2.7. Designandstatisticalanalysis

Treatments were arranged in randomized blocks with four

blocksandeightrepetitions,twoperblock.Datawereanalyzed

usingANOVAandtheTukeytest(P<0.05)usingStatisticalAnalysis

Systemsoftware(SAS,1999).

3. Resultsanddiscussion

3.1. Mineralcompositionofplantparts,plantgrowthand

biomassproduction

Table3showstheaveragevaluesoftheCa,Mg,Na,KandCl

contentinleaves,stemsandrootsofA.nummulariaat134DAT.

Theheightoftheplantsdifferedsigniﬁcantlyamongthe

treat-mentsat132DAT(Fig.2).Thevalueforthetreatmentat75%of

FCdidnotdifferfromthevalueforthetreatmentat95%ofFC.

Table3

Averagecontentsofcalcium,magnesium,sodium,potassiumandchlorineinleaves, stemsandrootsofAtriplexnummulariagrowninsalinesodicsoilat134DAT.

Element Leaf Stem Root

Ca(gkg−1) 5.24±0.544 1.55±0.385 3.40±1.099 Mg(gkg−1) 6.13±0.482 1.13±0.240 2.50±0.508 Na(gkg−1₎ _124.73_±_11.545 _13.01_±_4.514 _15.29_±_3.975

K(gkg−1₎ _19.33_±_4.320 _10.50_±_2.135 _7.09_±_1.852

Cl(gkg−1₎ _149.45_±_20.571 _26.52_±_5.582 _19.96_±_2.213

±standarddeviation(n=32samples)

However,theseheightsweregreaterthantheheightsfoundfor

thetreatmentsat35%and55%ofFC.Thestemdiameterforthe

treatmentswith75%and95%ofFCwassigniﬁcantlyhigherthan

thecorrespondingvaluesforthetreatmentswith35%and55%of

FC,formeasurementsmadeafter33,66and132DAT.

The plants grew steadily up to 66 days after transplanting

(Fig.2).At thisgrowthperiod, the75%FCtreatmentpresented

plants77.06cmhigh,inaverage,whiletheywereonly32.63high

atthebeginningoftheexperiment.Thissametreatment132days

aftertransplantingpresentedvaluesofmeanheighttoplantsof

88.60cm.Thisisequivalenttoonly11.59cmabovetheheight

mea-suredatthe66thday.Suchastabilizationofgrowthafter66days

wasprobablydue totheamountofsoilin thepots(20kg)that

impairedrootsdevelopment.

Neitherthevaluesofthefreshmassofleavesnorthevalues

ofthedrymassofleavesdifferedbetweenthetreatmentsat75%

and95%ofFC.However,thesevaluesexceededthecorresponding

valuesfortheothertreatments(Fig.3).Thevaluesforthefreshmass

andthedrymassofstemswerehigherforthetreatmentat75%of

FCthanfortheothertreatments.Thevaluesofthefreshmassof

rootsbehavedsimilarlytothevaluesfortheshoots(stem+leaves).

Theywerehighestforthetreatmentsat75%and95%ofFC.This

indicatesadirect relationshipbetweenrootssystemandshoots

aswellasprovidesdatatounderstandtheresponseonbiomass

yieldaccordingtosoilhumidity.Thehighertherootsfreshmass

thegreatertheabilitytowaterandnutrientsuptake.Thereforethe

useofA.numulariatoamelioratesalt-affectedareasisdependent

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Fig.2.Plantheight(cm)andstemdiameter(mm)ofAtriplexnummulariaLindl.at 6,33,66,96and132daysaftertransplanting(DAT)intermsofsoilmoisture.Means followedbysamelowercaseletterwithindateofevaluationamongthelevelof moisturedidnotdifferstatisticallybyTukeytest(P<0.05).

absorbingchlorineandsodium(Table3).Notonlytherootsfresh

mass(Fig.3)butalsothecontentsofchemicalelementspresent

inleaves,stem,androots(Table3)arefundamentaltoaproper

managementofthephytoextractionusingA.nummularia.

A.nummulariaLindl.iscommonlydescribedasaspecies

hav-ingahightolerancetosaltstressand towaterstress.However,

studiesonitstolerancetosoilswithlowwater contentarestill

scarce.Whensaltsareremovedfromthesoilbyusingplants

(phy-toremediation), biomassproductionmustbeoptimizedthrough

irrigation.Theleafdrymassatthelowestlevelofsoilmoisture

(35%ofFC)canbeusedforcomparativepurposes.Relativetothis

baselinevalue,leafdrymassintheothertreatments(55%,75%and

95%ofFC)increasedby21%,75%and81%,respectively.Theleafdry

massincreasedasafunctionofsoilmoisture.Thevaluesofleafdry

masswere9.41gplant−1at35%FCand17.02gplant−1at95%FC.

Thedrymassofstemsandrootsdecreasedforsoilat95%ofFC,

comparedwiththecorrespondingvaluesintheothertreatments.

Liuetal.(2008)havestudiedtheeffectsoflevelsofsoilmoisture

(40%,55%,70%and85%ofﬁeldcapacity)andNaClconcentrations

(0,50,100,150and200mmolL−1)onthegrowthofthehalophyte

Suaedasalsa.Theyfoundthattheplantgrewmorewhenthesoilwas

at55%ofFCforarangeofNaClconcentrationsof50–100mmolL−1.

At85%ofFC,theplantgrewmoreforarangeofNaCl

concentra-tionsabove100mmolL−1.Thisﬁndingindicatesthatwithgreater

availabilityofwater,thisspeciesbecomesmoretoleranttohigh

concentrationsofsaltsinthesoil.

Lealetal.(2008)assessedthepotentialofA.nummulariaforthe

phytoremediationofsodicsalinesoilirrigatedwithsalinewater.

At130DAT,theyfoundvaluesof12.98gplant−1 fortheshoots

(leaves+stems)and3.70gplant−1fortheroots.

3.2. Vesiculartrichomes

Vesicular trichomeswereobserved on both theadaxial and

abaxialsurfacesofA.nummularialeaves.Thevesiculartrichomes

37.36 C 57.57 B 80.21 A 90.95 A 0 20 40 60 80 100 F M o f leaf (g pl -1) 9.41 C 11.94 B 16.51 A 17.02 A 0 20 40 60 80 100 DM o f leaf (g pl -1) 24.06 D 34.29 C 50.55 A 43.32 B 20 30 40 50 60 F M o f stem (g pl -1) 13.36 D 17.98 C 27.21 A 22.61 B 0 15 30 45 60 DM o f st em (g pl -1) 42.66 B 48.13 B 91.87 A 73.72 A 0 20 40 60 80 100 30 50 70 90 110 F M o f ro o t (g pl -1)

Field Capacity(%)

13.77 C 15.21 BC 27.70 A 21.20 AB 0 20 40 60 80 100 30 50 70 90 110 DM o f ro o t (g pl -1) Field Capacity (%)

Fig.3. Freshanddrymass(gplant−1₎_of_leaf,_stem_and_root_of_Atriplex_nummularia_Lindl._at₁₃₄_DAT_in_terms_of_the_soil_moisture._Means_followed_by_same_uppercase_letter

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Fig.4. FrontviewoftheepidermisofmatureleavesofAtriplexnummulariaLindl.growninsodicsalinesoilunderdifferentwaterregimes:(a)35%;(b)55%;(c)75;(d)95% ofFC.Indetail,drusa(e)formedbydepositionofsodiumchloridewithincells.Vesiculartrichomeconsistingofstalkcellsurmountedbyavesicularcell(f–g)andstomata (h).sc:stalkcell;vc:vesicularcell;dr:drusa;st:stoma.Bar:50␮m(a–d),25␮m(e–h).

inthisspeciesconsistoftwoeasilydistinguishabletypesofcells

(Fig.4).Thestalkcelliselongatedandcylindrical,withathickwall

andavariablelengthanddiameter.Itissituateddirectlyonthe

epidermalbasalcell(Fig.4g).Thevesicularcellisglobularinshape.

However,thepressureexertedbyneighboringvesicularcellscan

causechangesinitsshape.Itdisplaysavariablediameterand

vol-ume,anditislocatedonthestalkcell.

Amongtheanatomicalfeaturesmeasuredandevaluated,only

thevesicleaveragediameter(VAD)andthevesicleaveragevolume

(VAV)variedamongthetreatments(Table4).

Thesmallestmeandiameterandmeanvolumeofvesicleswere

foundintheepidermisofplantsgrownat35%ofFC.Neitherthe

meandiameternorthemeanvolumeofvesiclesdifferedamong

plantsgrownat55%,75%and95%ofFC.

Vesicular trichomes showed a similar distribution, size and

volume on both sides of the epidermis. Signiﬁcant differences

betweentheabaxial and adaxialsurfaces wereobserved,

how-ever, for VAD and VAV in the treatment at 35% of FC. The

values of themean diameterand the mean volumewere both

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Table4

AnatomicalfeaturesoftheepidermisofmatureleavesofplantsofAtriplexnummulariaLindl.growninsodicsalinesoilunderdifferentwaterstresslevels.

SAD1_(␮m) _VAD_(␮m) _VAV₍₁₀6_␮m3_mm−2₎ _VTAD_n_mm−2

35%offieldcapacity Adaxial 20.54a Z 1,103.83a 30,085.70a Abaxial 21.62a 132.82b 563.74b 26,621.21a Mean 21.20A 149.10B 840.10B 29,250.30A 55%offieldcapacity Adaxial 20.24a 174.30a 1547.13a 27,108.48a Abaxial 21.23a 190.09a 1986.95a 25,242.69a Mean 20.65A 183.20A 1800.15A 26,500.85A 75%offieldcapacity Adaxial 20.50a 195.46a 2389.32a 30,879.04a Abaxial 21.21a 173.87a 1720.55a 27,709.64a Mean 20.78A 185.32A 2.070.80A 29,500.10A 95%offieldcapacity Adaxial 20.60a 171.74a 1057.79a 24,998.42b Abaxial 20.84a 168.22a 1436.57a 29,038.10a Mean 20.50A 170.10AB 1260.26AB 27,650.76A VC(%) 4.55 7.69 27.51 12.65

1_SAD:_stalk_average_diameter;_VAD:_vesicle_average_diameter;_VAV:_vesicle_average_volume;_VTAD:_vesicular_trichomes_average_density;_VC:_variation_{coefﬁcient.}_Means

followedbysamelowercaseletterwithineachlevelofmoistureanduppercasebetweenthelevelsdidnotdifferstatisticallybyTukeytest(P<0.05).

Table5

Coefﬁcientsofsimplelinearcorrelationbetweenelectricalconductivity(ECes),osmoticpotential(OPse),solublebasesandchlorideofsaturationextractattheendofthe

experiment. ECse OPse Ca2+ Mg2+ Na+ K+ Cl− ECse – 0.85** 0.75** 0.83** 0.90** 0.92** 0.85** OPse – 0.73** 0.80** 0.84** 0.85** 0.84** Ca2+ _– _0.93** _0.73** _0.76** _0.74** Mg2+ _– _0.81** _0.82** _0.82** Na+ _– _0.88** _0.85** K+ _– _0.88** Cl− _–

**_Highly_signiﬁcant_(P_<_0.01),_n₌₉₇_samples.

FC,themeanvesicledensity washigherontheabaxial

epider-mis.

Itiscommontoﬁndvesiculartrichomescoveringtheentire

epi-dermisinspeciesofAtriplex(Mozafar&Goodin,1970;Boughalleb

etal., 2009).However,thedetails ofthis morphology canvary

among species. A. nummularia is similar to Atriplextriangularis

(Karimi&Ungar,1989).Thelatterspeciesexhibitsvesicular

tri-chomes formedby a vesicular cell that binds tothe epidermis

througha single-celledstalk. In contrast,Atriplexhalimushasa

multicellularstalk.Inadulttrichomesofthisspecies,thestalkcan

consistofuptothreecells.Atriplexspeciesaccumulatethehighest

concentrationsofsaltsinthevesiculartrichomes.However,inthis

study,thestalkcell,unlikethevesicularcell,didnotrespondto

dif-ferencesinthelevelofwaterstress.Becausethestalkrepresentsthe

connectionbetweentheepidermalandvesicularcells(

Appezzarto-da-Glória&Carmello-Guerreiro,2006),changesinthestructureof

thestalkcellcouldaffecttheplant’sabilitytotransportsaltfrom

theepidermalcellstothevesicularcellsandstoreitinthe

vesic-ularcells.However,noassociationwasfoundbetweenthemean

diameterofthestemsandthemeandiameterofthevesicles.

Thedensitydistributionoftrichomesperunitareaofthe

epi-dermisdidnot differsigniﬁcantly among treatments.However,

decreases in diameter and vesicular cell volume per unit area

resultedfromtheexperimentalreductionofwatercontent

asso-ciatedwithincreasingwaterstress.Thisﬁndingmayindicatethat

Atriplexplants grown insodicsalinesoil managedtomaintain

highercellturgorathigherwatercontentsinthesoil.

A.nummulariagenerallytoleratesdryness.However,alevelof

35%ofFChad anegativeeffectonthemeanvolumeoftheleaf

vesiclesoftheplant(Table4).Thisﬁndingmayindicateadecreased

amountofsaltaccumulationandthereforeareducedlevelofNa

accumulationbytheplant.

3.3. Osmoticpotential

ThecorrelationsbetweenEC,osmoticpotentialandthe

con-tentofCa2+_,_Mg2+_,_Na+_,_K+_and_Cl−_in_the_extract_from_saturated

soil(Table5)conﬁrmtheassumptionsofBen-Galetal.(2009).The

correlationcoefﬁcientofECse withCa2+was0.75(P<0.01),and

thecorrelationcoefﬁcientofECsewithK+was0.92(P<0.01).The

correlationcoefﬁcientofECsewiththeosmoticpotentialwas0.85

(P<0.01).Thecorrelationcoefﬁcientsoftheosmoticpotentialwith

theothervariablesremainedmorestable(Ca:0.73;Mg:0.80;Na:

0.84;K:0.85andCl−:0.84(P<0.01).Thisstabilityprobablyresulted

fromthefactthatcertainions(e.g.,Na+_and_K+₎_inﬂuence_the_EC

morestronglythandoothers(e.g.,Ca2+_and_Mg2+_).

The results shown in Table 6 explain why Atriplex is able

to absorb water in environments in which other crops

can-not do so. In the extract from saturated soil, the average

Table6

DescriptivestatisticsofECse,OPoftheextractofsoilsaturation(OPse)andOPofthe

leafsap(OPls).

Parameters ECse(dSm−1₎ _OP_se_(atm) _OP_ls_(atm)

Mean 39.34 −16.80 −49.29 Minimumvalue 15.50 −34.00 −70.03 Maximunvalue 63.76 −3.90 −36.29 Standarddeviation 20.24 6.50 6.00 Variationcoefﬁcient(%) 51.45 38.77 12.15 Numberofsamples 97 97 27

(7)

Table7

Averagevaluesofelectricalconductivity(EC)andosmoticpotentialofthesaturationextract(OP)beforeandaftercultivationofAtriplexasafunctionofhumiditylevelsand valuesofmatricpotential.

Treatments Beforecultivation Aftercultivation Beforecultivation Aftercultivation

ECse(dSm−1) OP(MPa) 35%ofFC(−1.69MPaa₎ _40.07_a_A _37.72_a_AB _−0.74_b_AB _−1.46_a_AB 55%ofFC(−0.73MPa) 42.26aA 39.06aAB −0.82bAB −1.57aAB 75%ofFC(−0.025MPa) 39.53aA 35.70aB −0.57bB −1.31aB 95%ofFC(−0.054MPa) 46.04aA 43.49aA −1.09bA −1.84aA Control(−0.054MPa) 47.24aA 45.65aA −1.04bAB −1.72aAB

a_The_values_of_matric_potential_were_estimated_according_to_the_soil–water_{characteristic}_curve.

ECse was 39.34dSm−1 and the average osmotic potential was

−16.80atm(−1.68MPa),whereasthemeanleafosmoticpotential

was−49.29atm(−4.929MPa).

Themain criteriaforassessingcroptolerancetosalinityand

forthemanagementofbiosalineagriculturearetheconcentrations

ofchemicalelementsand/orelectricalconductivity.Ben-Galetal.

(2009)havesuggestedtheuseofosmoticpotentialasanindexto

assesstheseeffects.Theyemphasizethatexperimentswithcrops

suchasbeans,corn,tomatoes,onionsandalfalfahaveindicatedthat

saltscontainingdifferentcations(Na+_,_Ca2+_and_Mg2+₎_and_anions

(Cl−,SO42−)donotaffectplantgrowthwhenevaluatedin

isola-tion.Theconverseofthisresultholdsfortheosmoticpotential.

Manystudiesinplantphysiologyaddressonlytheeffectsofspeciﬁc

saltssuchasNaCl.Accordingly,duetothecomplexityofchemical

speciesfoundinsoilsolutions,itisalsonecessarytoevaluatethe

interactionsofthesesaltswithotherelements.

Ben-Galetal.(2009)havecompareddifferentwaysof

assess-ingtheeffectsofsalttoxicityinmelon,cornandbeanplants.They

consideredtheactionofindividualions,theelectrolyte

concentra-tionandtheosmoticpotential.Ifsalinitywasexpressedintermsof

osmoticpotential,themodelsfoundyieldedthebestadjustments,

andtheidentiﬁcationofthecationsinvolvedprovedirrelevant.

Welackstudiesofwaterrelationsinthesoil–water–plant

sys-teminsalineenvironments.Thehighconcentrationsofsaltsfound

intheseenvironmentsalterstheosmoticpotential,oneofthemain

waterpotentialsinthesoil.Typically,innon-salineenvironments,

theimportance of this potential is overlooked because it does

notinﬂuencethewaterconstantsthispotentialisoverlookedfor

notinﬂuencingthewaterconstants.Measurementoftheosmotic

potentialisof greatimportanceinsalineenvironmentsbecause

ithasadirect relationshipwiththeabsorptionof waterbythe

plant.

InA.nummulariagrowninasolutionof150mmolL−1ofNaCl

(∼15dSm−1),theosmoticpotentialinleaveshasbeenfoundtobe

approximately5–6timeslowerthanthatintherootsandinthe

externalsolution(Silveiraetal.,2009).Valuesof−4.03,−0.64and

−0.83MPawerefoundfortheleaves,therootsandthesoilsolution,

respectively.

Toachievealowerosmoticpotential,primarilyintheleaf,the

plantsequestersNa+ _and _Cl− _in _the _vacuole._It _decreases_their

concentrationinthecytoplasmandperformsappropriateosmotic

adjustments to maintainwater uptake in saline soils.In

addi-tiontothecompartmentalizationofNa+_and_Cl−_in_the_vacuole,

plantssynthesizeandaccumulateorganiccompoundsinthe

cyto-plasm.These solutesprotect the damaged cellularcomponents

fromdehydrationandarecommonlyreferredtoasosmoprotectors.

Such solutesincludeproline, sugars(sucrose, fructose,glucose)

andcomplex sugars(trehalose),polyols (mannitol,glyceroland

methylatedinositol)andquaternaryammoniumcompoundssuch

asglycine, betaine,alaninabetaine, prolinabetaine,and

hydrox-yprolinabetaine(Chinnusamyetal.,2005;Ashraf&Foolad,2007;

Flowers&Colmer,2008;Munns&Tester,2008;Türkan&Demiral, 2009).

Theverynegativevaluesofosmoticpotentialreachedintheleaf

sap(Table6)allowedA.nummulariatoabsorbwaterevenfromsoil

withhighsalinity.Thisabilityallowstheplanttodevelopinthe

presenceofwaterstressandsalinity,forexample,inenvironments

withsalt-affectedsoilsandasemiaridclimate.Ingeneral,these

ﬁndingsconﬁrmthatA.nummulariarepresentsaverypromising

salt-phytoextractorspecies.

3.4. Evolutionofelectricalconductivityandosmoticpotential

duringtheAtriplexcultivation

Themaincomponentsinﬂuencingwatertotalpotentialinsoil

are the matric and osmoticpotentials. Thus is of fundamental

importancetodeterminesuchpotentialsinordertoassesstheir

effectsonplantsgrowth.Thevaluesforelectricalconductivityof

thesaturationextractdidnotpresentstatisticaldifferencesbefore

andaftertheAtriplexgrowing(Table7).Thiswasnoteddespiteall

thetreatmentspresentedsaltsenteringthesystemthroughwater

addition.Thisshouldincreaseelectricalconductivitytakinginto

accountthatleachingfractionswerenotused.Suchresult

corrob-oratestheweaknessoftheelectricalconductivitymeasurewhen

assessingsoilsalinity(Ben-Galetal.,2009)

Therewas a signiﬁcantdifference for the osmoticpotential

beforeandaftercultivation(Table7).Thisindicatesthat,contraryto

observedtotheelectricalconductivity,thepotentialosmotic

mea-surewasusefultodetectaccumulationofchemicalelementsadded

viairrigationwater.Ontheotherhand,boththeosmoticpotential

andtheelectricalconductivitydidnotdifferedamongtreatments

probablyduetoconcentrationeffectonthetreatmentswithlowest

humidity.ThegrowthdecreasingofAtriplexfortheselowestlevels

ofFCinsoilinspiteofthesamesalinitylevelsobservedwasdueto

hightoleranceofthespeciestohighcontentsofsalts.Theplants

tol-eratethesalttoxicitybutwereaffectedbyreducedvaluesofmatric

potential.Thesepotentialsrangedfrom−1.69MPato−0.73MPa

for the treatments 35% and 55% FC, respectively. It is

impor-tanttopointoutthatthepermanentwiltingpointisconsidered

tobe−1.5MPa.

Onthisscenario,theeffectofhydricstresswasmore

impor-tantthansalinestress.However,theeffectofbothstressesmustbe

takenintoconsiderationsincetheydiminishedthetotalpotential

ofwaterinsoilandwateravailabilitytoplants.Forinstance,the

valueof−1.69MPaforthematricpotentialat35%FCplusthevalue

ofosmoticpotential(−1.46MPa)forthesametreatmentsumsup

−3.15MPa.Thisoncemorecorroboratestheimportanceof

assess-ingnotonlythematricpotentialbutalsotheosmoticpotential

inordertobetterunderstandingthegrowthofAtriplexplantson

salt-affectedsoils.

4. Conclusions

Thestudyofthegrowthpatternsandanatomicalchangesshown

(8)

moistureconditions cancontributesigniﬁcantlytothe

manage-mentofsoilandwaterinsemiaridregions.Theresultsofthecurrent

studyshowthattheheight,diameterandfreshanddrybiomass

ofleaves,stemsandrootsofA.nummulariaLindl.weresensitive

tosoilmoisture.Thebestresultswereobtainedwhentheplants

weregrownatsoilmoisturecontentlevelsof75%and95%ofﬁeld

capacity.Variationsinthesoilwatercontenttriggeredanatomical

changesinthevesiculartrichomesoftheleaves.Alowwater

con-tentinthesoilisrelatedtosmallaveragediametersandvolumesof

theepidermalvesicles.Themeasurementoftheosmoticpotential

canprovideagoodindexforevaluatingplantresponsestowater

stressandsalinity.

Acknowledgments

ThepresentstudywasﬁnancedbyNationalCouncilfor

Scien-tiﬁcandTechnologicalDevelopment(CNPq).Theauthorsarealso

indebtedtotheFederalRuralUniversityofPernambucoStatefor

itssupport.

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