Arbuscular mycorrhizal fungi in Mimosa tenuiflora (Willd.) Poir from Brazilian semi-arid

h tt p : / / w w w . b j m i c r o b i o l . c o m . b r /

Environmental

Microbiology

Arbuscular

mycorrhizal

fungi

in

Mimosa

tenuiflora

(Willd.)

Poir

from

Brazilian

semi-arid

Tancredo

Augusto

Feitosa

de

Souza

_,

_Susana

_{Rodriguez-Echeverría}

_,

Leonaldo

Alves

de

Andrade

_,

_Helena

_Freitas

a_{AgrarianScienceCenter,DepartmentofSoilsandRuralEngineering,FederalUniversityofParaíba,Areia,Paraíba,Brazil} b_{CentreforFunctionalEcology,DepartmentofLifeSciences,UniversityofCoimbra,Coimbra,Portugal}

a

r

t

i

c

l

e

i

n

f

o

Received12April2015

Accepted21September2015

Availableonline2March2016

AssociateEditor:AndréRodrigues

Keywords:

AMFcommunitystructure

AMF-plantpairing

Dryland Glomeromycota

a

b

s

t

r

a

c

t

ManyplantspeciesfromBraziliansemi-aridpresentarbuscularmycorrhizalfungi(AMF)

intheirrhizosphere.Thesemicroorganismsplayakeyroleintheestablishment,growth,

survivalofplantsandprotectionagainstdrought,pathogenicfungiandnematodes.This

studypresentsaquantitativeanalysisoftheAMFspeciesassociatedwithMimosatenuiflora,

animportantnativeplantoftheCaatingaflora.AMFdiversity,sporeabundanceandroot

colonizationwereestimatedinsevensamplinglocationsintheCearáandParaíbaStates,

duringSeptemberof2012.Thereweresignificantdifferencesinsoilproperties,spore

abun-dance,percentageofrootcolonization,andAMFdiversityamongsites.Altogether,18AMF

specieswereidentified,andsporesofthegeneraAcaulospora,Claroideoglomus,Dentiscutata,

Entrophospora,Funneliformis,Gigaspora,Glomus,Racocetra,RhizoglomusandScutellosporawere

observed.AMFspeciesdiversityandtheirsporeabundancefoundinM.tenuiflorarhizosphere

shownthatthisnativeplantspeciesisanimportanthostplanttoAMFcommunitiesfrom

Braziliansemi-aridregion.Weconcludedthat:(a)duringthedryperiodandinsemi-arid

conditions,thereisahighsporeproductioninM.tenuiflorarootzone;and(b)soilproperties,

assoilpHandavailablephosphorous,affectAMFspeciesdiversity,thusconstitutingkey

factorsforthesimilarity/dissimilarityofAMFcommunitiesintheM.tenuiflorarootzone

amongsites.

©2016SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.Thisis

anopenaccessarticleundertheCCBY-NC-NDlicense

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

The Brazilian semi-arid region is an important Caatinga

ecoregionthatprovidestherequiredbioticandabiotic

con-ditionsfor many endemic species to inhabit; thus, having

∗ _{Correspondingauthor.}

E-mail:tancredoagro@hotmail.com(T.A.F.deSouza).

highspeciesdiversitywhencomparedwithothersemi-arid

regions ofthe World. This ecoregioncovers approximately

12% ofthecountry,and islocatedinthe innermostregion

of northeastern Brazil. It is characterized by frequent dry

periods,andbyauniquebiota,withthousandsofendemic

speciesandover1000speciesofvascularplant.1,2 _However,

http://dx.doi.org/10.1016/j.bjm.2016.01.023

1517-8382/©2016SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.ThisisanopenaccessarticleundertheCC

the establishment, growth and dispersal of native

vegeta-tion areoftenrestricted bylongdry periodsanthropogenic

activities,andexoticspeciesintroduction.1

Inthiscontext,plantmutualisticinteractionswithother

organisms,suchasfungi,mightplayasignificantrole

dur-ing their establishmentand growth. Mutualistic symbiosis

betweenarbuscular mycorrhizalfungi(AMF)and plantsare

advantageousforbothorganismsinvolved,becausetheplant

providestheAMFwithenergeticproductsresultingfrom

pho-tosynthesis,allowing AMFgrowth and maintenance,while

AMFprovidestheplantwithwaterandmineralnutrients,such

asphosphorusandnitrogen.3,4_{Byenhancingplant’smineral}

nutrientsuptake,AMFplayakeyroleintheestablishmentand

survivalofnativeplantsinthisbiome,promoteplantgrowth

andofferprotectionagainstdroughtandsoilpathogens.5–8

Mimosa tenuiflora (Willd.) Poir (Fabaceae) is a perennial

native plant from northeastern Brazil. Similarly to other

Fabaceae,M.tenuifloraisabletofixnitrogenbecauseitsroots

formassociations withbacteria fromthegenusRhizobium.9

Thisplantspeciesisconsideredtobeaprolificpioneerplant,10

whichisverytoleranttodryperiods,firesandothermajor

eco-logicaldisturbances.11_{Duringhighlystressperiods,itsleaves}

starttofall,representingamechanismfortheplanttosave

energy.10_{Itdevelopsextensiverootsystems,whichare}

colo-nizedbymutualisticorganisms,asbacteriaandfungi.Indeed,

previousstudies haveshown theassociation betweenAMF

andM.tenuiflorarootsystem.9,12,13_{Theprimarilyobjectiveof}

moststudiesconductedhavebeentoverifythepresenceof

AMF,butmorerecently,theyhavefocusedontheAMFspecies

diversitycommonlyfoundassociatedwithnativespeciesof

the Brazilian semi-arid region. Those studies have shown

thatspeciesfrom thegeneraArchaeospora,Acaulospora,

Glo-mus,GigasporaandScutellosporafrequentlyformmutualistic

symbiosiswithnativeplantspecies.14,15

Soil fertility is often reported as an important factor

conditioningAMFspeciesdiversity,havingeffectsatthe

com-munity level, but also on the biological activity of these

microorganisms.16–19_{Thus,theobjectiveofthepresentstudy}

wastoprovideaquantitativeassessmentoftheAMFspecies

associatedwithM.tenuifloraintheBrazilianxericshrublands

sampledfromdifferentlocationsacrosstheCearáandParaíba

States.Toaccomplishthisobjective,weselectedseven

inde-pendentsiteswherewesampledM.tenuiflorarootzoneandwe

hypothesizedthat(1)therootzoneofthisnativeplantspecies

hashighAMFsporeabundanceandrootcolonizationduring

thedryperiod;and(2)soilpropertiesareanimportantfactor

thatinfluencetheAMFcommunityindifferentM.tenuiflora

rootzones.

Materials

and

methods

Sitedescriptionandsampling

Samplingofthestudyspeciesrootzoneareawasperformed

inlocations withsimilarimportancevalueindex20 _(IVI,see

tablebelow)ofM.tenuiflorainCearáandParaíbaStates,Brazil

(Table1).Duringthedryseason,theaverageannual

temper-atureisof30◦C,whileduringtherainyseason,theaverage

annualtemperatureisaround23◦C.Rainfallinthegreaterpart

ofthisregionisscanty,unpredictableandirregular.1_The

flow-eringseasonforM.tenuiflorastartsonAugustinCearáState,

one monthearlier than ParaíbaState. Theflowering starts

aftertherainyseason(August)andduringthedryseasonthat

theplantgrowthisverylimited.

Ineachsite,weestablished40plotsof100m2_,accordingly

tothemethodologyproposedbyGrieg-smith22_andFortinand

Dale.23_{BeforesamplingM.tenuiflorarootzone,thefollowing}

criteriawereestablished:(a)eachplantshouldbelargerthan

3cmindiameternearsoilsurface;(b)itsheightshouldvary

between1and3m;and(c)noother individualsfroma

dif-ferent plantspecies shouldoccur atadistance lower than

3mfrom the sampling point.23–27 _{Intotal, twenty-fiveroot}

zonesamplesperplotincludingsoilandrootfragmentswere

collected atadepthrangingbetween0and20cm.Soilwas

keptinplasticbagsandrootfragmentswerestoredin50%

ethanoluntillaboratoryanalysis.Becausefungalsporulation

is expectedtobehigher duringthedry periodinsemiarid

environments,15_{thesamplingwasconductedduring}

Septem-berof2012.

Soilanalyses

For eachplot, soilandrootssampleswerepooledresulting

in40samplespersite.Ineachofthesesamples,thefollowing

variablesweremeasured:pH,carbon,totalnitrogenand

avail-ablephosphorus.SoilpHwasdeterminedinasuspensionof

soilanddistilledwater28_{;soilorganiccarbonwasestimated}

accordinglytothemethodologydescribedbyOkalebo29_;total

soilnitrogen content wasestimatedfollowing theKjeldahl

method28_{; andavailablephosphorus wasdetermined}

spec-trophotometrically followingthe molybdenumbluemethod

andusingstannouschlorideasthereducingagent.28

Sporesassessment

Spores were extracted from field soil samples (n=40) by

wet sieving30 _{followed bysucrosecentrifugation.}31 _Initially,

the extracted spores were examined in aqueous solution

under a dissecting microscope and separated based on

morphologicalcharacteristics.Then,polyvinylalcohol

lacto-glycerol(PVLG)mixedornotwithMelzer’sreagentwasused

as permanent mounting medium.32 _{Species identification}

was based on the descriptions provided by Schenck and

Perez,33 _{publications with descriptions of new genera and}

families,34 _{and by consultingthe international culture}

col-lection ofarbuscular mycorrhizal fungi database – INVAM

(http://invam.caf.wvu.edu).Forthepurposeofthiswork,we

adoptedtheclassificationproposedbyOehletal.,35_including

recentlydescribednewtaxa.36–38

Mycorrhizalrootcolonizationassessment

To assess mycorrhizal root colonization, roots were first

cleared in2% KOH for1h at90◦C, and subsequently they

were acidifiedin1%HCl overnight.Blueink(Parker Quink)

was used as staining agent for 30min at 60◦C, followed

byadestainingtreatmentwithlactoglycerol.Theextentof

mycorrhizalrootcolonizationwasestimatedbyusinga

Table1–Geographiccoordinatesandtheimportancevalueindex(IVI,%)ofM.tenuifloraplantsineachstudiedsite.

Studyarea Location Geographicalcoordinates IVI(%)c

A1 AlgodãodeJandaíra,PB 06◦₄₆_7.3_S36◦₀₁_55.3_{W 59.02±1.12} A2 Esperanc¸a,PB 06◦5645.7S35◦5406.8W 58.12±0.52 A3 Ibaretama,CE 04◦4946.8S38◦3847.6W 60.01±1.87 A4 Juazeirinho,PB 07◦0633.3S36◦3434.2W 59.13±1.13 A5 Monteiro,PB 07◦4819.8S37◦1032.4W 58.01±2.17 A6 Natuba,PB 07◦3734.9S35◦3224.5W 59.18±1.56 A7 Poc¸inhos,PB 07◦1023.3S36◦1241.8W 60.12±1.98

Climateclassificationa _Hotsemiarid

Textureandsoilclassificationb _{SandyloamDystricFluvisols}

a _{AccordinglytotheKöppenclassification.}

b _WRB.21

c _{IVI(%)=RDi+RFi+RDoi;RDi,RFiandRDoiforrelativedensity,relativefrequencyandrelativedominanceofM.tenuifloraineachstudyarea}

accordinglytoMagurran.20_{Valuesaregivenasmean±SE,n=40.}

acompoundmicroscopeat200×magnification.39,40 _Priorto

microscope examinations, we decided to score hyphae as

“mycorrhizal”,basedontheassociatedpresenceofvesicles,

arbuscules, spores, and the morphology of the mycelium.

Thus, if any of the structures referred were found in one

of the 100 microscope intersections per sample per study

site(n=400intersectionsperstudysite),theywerescoredas

“mycorrhizal”.Toavoid errorassociatedwith theobserver,

allmicroscopicexaminationswere carriedoutbythesame

individual.

Statisticalanalysis

One-way ANOVA was used to compare spore abundance

and rootcolonizationamong the sevenlocations sampled.

The relationship between the AMF community structure

and soil propertieswas examined bycalculating the

Pear-son correlation coefficient. To explore the variability and

similarities among soils and AMF communities

composi-tion among sites, principal component analysis (PCA) was

used.

The following ecological indexes were calculated after

AMFspeciesidentification:averagespeciesrichnessofAMF,

diversity index41 _{and dominance index}42 _{for each studied}

site. One-way ANOVA was used to compare species

rich-nessofAMF,the diversityindex andthe dominanceindex

amongsites.Inaddition,theZhang’sfrequencyofoccurrence

classification43_{wasusedtoanalyze(a)totalsporeabundance}

(totalnumberofspores),(b)sporeabundanceofagivenAMF

species(numberofsporesofaparticularAMFspecies),and

(c) AMFspecies occurrence frequency (percentage of

sam-ples containing a particular AMF species). This procedure

allowedAMFspeciestobeclassifiedasdominant(FO>50%),

mostcommon (31≤FO≤50%), common (10≤FO≤30%)and

rare(FO<10%).43_{Additionally,AMFspecieswerealso}

classi-fiedasgeneralists(presentinsixareas),intermediate(present

in two to five areas) or exclusive (restricted to only one

area).44

Beforestatisticalanalysis,datawascheckedfornormality

andhomogeneityofvariances.One-wayANOVAandthe

Pear-soncorrelationcoefficientswere calculatedusing SAS9.1.3

Portable,whilePCAanalysisandtheecologicalindex

calcula-tionswereconductedusingMVSP3.1.45

Results

Allsoilchemicalpropertiesvariedsignificantlyamongsites

(Table2).AccordinglytothePCAanalysis,A4andA6werethe

mostdissimilarlocations(Fig.1).A1andA2weremore

sim-ilar toeachother thanA3,A5andA7.Totalorganic carbon

andavailablephosphorouswerethemainfactors

contribut-ing tothe varianceofmostsamples.PCAplotalsoshowed

astrongpositiverelationshipbetweentotalnitrogen,soilpH

andavailablephosphorousand93.1%ofthesamples’variation

wasexplainedbythetwoaxes.

Sporeabundanceandrootcolonization

SitesA4andA5didnotsignificantlydifferinsporeabundance

data,showingthehighestvaluesfromallstudiedsites,

aver-aging16.6sporesg−1soiland15.3sporesg−1soil,respectively

(Fig.2).Intheremainingfivesites,wefoundstatistically

sig-nificantdifferences(p<0.05)whencomparingA1,A2andA6

withA3andA7.A7hadthesmallestvalueofsporeabundance

fromallstudiedsites(6.8sporesg−1soil).Statistically

signifi-cantdifferences(p<0.05)werealsofoundinrootcolonization

amongallsites(averagesrangingbetween6.3and36.5%).A2

hadthehighestrootcolonization,whileA1thesmallestofall

studiedsites(Fig.2).

AMFcommunitydiversityandstructure

Ecologicalindexessignificantlydifferedamongsites(p<0.05).

AMFtotalrichnessvariedbetween14and18species,the

diver-sityindexrangedbetween1.98and2.64,andthevaluesforthe

dominanceindexaveragedbetween0.80and0.91amongsites.

A4sitehadthehighestvaluesforallecologicalindexes

calcu-lated(speciesrichness,18species;diversityindex,2.64;and

dominanceindex,0.91;Table3).

Field-collected sporeswere from twoorders,

Table2–Soilchemicalpropertiesforeachsampledlocation.Valuesaregivenasmean±SE(n=40). Parameters A1 A2 A3 A4 A5 A6 A7 LSD pH(H2O) 7.3±0.20 6.6±0.20 6.7±0.20 4.6±0.10 6.2±0.20 4.4±0.10 7.7±0.40 0.30 TOC(gkg−1) 19.3±0.60 8.2±0.20 4.8±0.30 17.8±0.20 18.5±2.80 6.2±0.20 9.2±1.00 14.40 P(mgkg−1) 8.6±0.30 8.2±0.20 6.5±1.40 3.4±0.10 7.8±0.60 0.8±0.30 12.3±2.40 1.50 Ntotal(gkg−1) 0.2±0.01 0.9±0.02 0.2±0.01 0.3±0.01 0.3±0.01 0.5±0.04 1.1±0.03 0.36

A1–AlgodãodeJandaíra,PB;A2–Esperanc¸a,PB;A3–Ibaretama,CE;A4–Juazeirinho,PB;A5–Monteiro,PB;A6–Natuba,PB;A7–Poc¸inhos,PB.

0.8 0.7 0.5 0.3 0.2 TOC –0.2 –0.7 –0.5 –0.3 –0.2 0.3 0.5 0.7P 0.8 –0.3 –0.5 –0.7 0.2PH A4 A6 A5 A1 A7 A2 A3 Axis 2= 27.53 Axis 1=65.57% Vector scaline: 0.72

Fig.1–PCAscoreplotofsoilpropertiesforthesevenstudiedsites.A1–AlgodãodeJandaíra,PB;A2–Esperanc¸a,PB;A3– Ibaretama,CE;A4–Juazeirinho,PB;A5–Monteiro,PB;A6–Natuba,PB;A7–Poc¸inhos,PB.Pointsrepresentsamplesfrom eachplotbystudiedsites.

families and four genera). Representatives belonging to four familiesofDiversisporaleswere identified: Acaulospo-raceaeDiversisporaceae,Entrophosporaceae,Gigasporaceae;

while two families from Glomerales were recognized,

Claroideoglomeraceae and Glomeraceae, representing ten

genera – Acaulospora (2), Claroideoglomus (1), Dentiscutata

(3), Entrophospora (1), Funneliformis (3), Gigaspora (3), Glomus

(1), Racocetra (1), Rhizoglomus (2) and Scutellospora (1); in

a total of 18 different AMF species. Accordingly to their occurrencefrequency,AMFspecieswere classifiedinto two groups: rare AMF species (R, occurrence frequency lower

than 10%), and common AMF species (C, occurrence

fre-quency between 10 and 30%). The AMF species identified

as rare species were: Acaulospora denticulata, Acaulospora

tuberculata, Dentiscutata cerradensis, Dentiscutata erythropus,

Dentiscutataheterograma,Entrophosporainfrequens,Funneliformis

caledonium, Funneliformis geosporum, Funneliformis mosseae,

Gigasporagigantea,Glomusmulticaule,Racocetracoralloidea,

Rhi-zoglomus aggregatum, Scutellospora calospora, Claroideoglomus

etunicatum, Gigaspora albida, Gigaspora decipiens, and

Rhi-zoglomus clarum were classified as common species. No

AMFspecieshadanoccurrencefrequencyhigherthan 30%

(Table4).

The PCA analyses showed that AMF species richness,

Shanonindex,Simpsonindex,soilpH,totalorganic carbon

andavailablephosphorouswerethemainfactors

contribut-ingtothevarianceofthesamples(Fig.3).Theanalysisalso

showed:(1)astrongnegativerelationshipbetweentotalsoil

pHandavailablephosphorouswithAMFspeciesrichness;and

(2)anegativerelationshipbetweentotalorganiccarbonand

Table3–Ecologicalindexescalculatedforeachlocation.Valuesaregivenasmean±SD(n=40).

Ecologicalindex Studiedsites

A1 A2 A3 A4 A5 A6 A7

Speciesrichness 18a 17a 17a 18a 15b 17a 14b

Shannonindex 2.20±0.02c 2.17±0.01c 2.42±0.08b 2.64±0.02a 1.98±0.04d 2.58±0.06a 2.16±0.07c

Simpsonindex 0.86±0.01b 0.85±0.01b 0.89±0.01a 0.91±0.01a 0.80±0.01c 0.91±0.01a 0.85±0.01b

A1–AlgodãodeJandaíra,PB;A2–Esperanc¸a,PB;A3–Ibaretama,CE;A4–Juazeirinho,PB;A5–Monteiro,PB;A6–Natuba,PB;A7–Poc¸inhos,

Table4–Occurrencefrequency(FOi)oftheAMFspeciesidentified.Valuesaregivenaspercentagefollowedbytheir occurrencefrequencyclassificationbetweenparenthesesaccordinglytoZhangetal.43

AMFspecies FOi(%)

A1 A2 A3 A4 A5 A6 A7

OrderDiversisporales

FamilyAcaulosporaceae

AcaulosporadenticulataSieverd.&S.Toro 4.8(R) 4.9(R) 3.2(R) 3.7(R) 2.0(R) 2.6(R) 2.2(R)

AcaulosporatuberculataJanos&Trappe 0.4(R) 0.4(R) 1.6(R) 0.5(R) 0.8(R) – –

FamilyEntrophosporaceae

Entrophosporainfrequens(I.R.Hall)R.N.Ames&R.W. Schneid.

0.5(R) 0.6(R) 1.7(R) 0.5(R) – 3.8(R) 0.5(R)

FamilyGigasporaceae

Dentiscutatacerradensis(Spain&J.Miranda)Sieverd.,

F.A.Souza&Oehl

1.6(R) 1.5(R) 2.5(R) 4.3(R) – 1.6(R) 2.3(R)

Dentiscutataerythropus(Koske&C.Walker)C.

Walker&D.Redecker

0.7(R) 0.6(R) 1.3(R) 6.5(R) 1.4(R) 11.5(C) –

Dentiscutataheterograma(T.H.Nicolson&Gerd.)

Sieverd.,F.A.Souza&Oehl

7.2(R) 7.3(R) 10.7(C) 15.8(C) 2.6(R) 2.3(R) 8.5(R)

GigasporaalbidaN.C.Schenck&G.S.Sm. 18.2(C) 18.0(C) 14.4(C) 4.7(R) 24.8(C) 7.8(R) 17.3(C)

GigasporadecipiensI.R.Hall&L.K.Abbott 17.4(C) 17.5(C) 10.8(C) 7.8(R) 24.6(R) 7.0(R) 14.9(R)

Gigasporagigantea(T.H.Nicolson&Gerd.)Gerd.& Trappe

0.2(R) 0.7(R) 1.7(R) 4.2(R) 1.6(R) 5.7(R) 3.2(R)

Racocetracoralloidea(Trappe,Gerd.&I.Ho)Oehl,F.A.

Souza&Sieverd.

3.0(R) 2.0(R) 4.0(R) 10.7(C) 3.5(R) 6.4(R) –

Scutellosporacalospora(T.H.Nicolson&Gerd.)C.

Walker&F.E.Sanders

1.2(R) 1.0(R) 2.4(R) 3.6(R) 1.8(R) 2.0(R) 1.6(R)

OrderGlomerales

FamilyClaroideoglomeraceae

Claroideoglomusetunicatum(W.N.Becker&Gerd.)C.

Walker&Schuessler

18.2(C) 19.5(C) 16.0(C) 4.8(R) 4.3(R) 6.0(R) 25.1(C)

FamilyGlomeraceae

Funneliformiscaledonium(T.H.Nicolson&Gerd.)C.

Walker&Schuessler

0.2(R) 0.4(R) 1.2(R) 2.5(R) 1.7(R) 1.5(R) 1.3(R)

Funneliformisgeosporum(T.H.Nicolson&Gerd.)C.

Walker&Schuessler

0.2(R) 0.7(R) 1.5(R) 3.9(R) 2.0(R) 4.9(R) 1.3(R)

Funneliformismosseae(T.H.Nicolson&Gerd.)C.

Walker&Schuessler

1.5(R) 2.9(R) – 7.7(R) 2.2(R) 7.7(R) 5.0(R)

GlomusmulticauleGerd.&B.K.Bakshi 5.0(R) 4.9(R) 6.5(R) 3.9(R) 2.3(R) 7.7(R) 8.2(R)

Rhizoglomusaggregatum(N.C.Schenck&G.S.Sm.)

Sieverd.,G.A.Silva&Oehl

2.7(R) – 5.0(R) 10.9(C) – 6.3(R) –

Rhizoglomusclarum(T.H.Nicolson&N.C.Schenck)

Sieverd.,G.A.Silva&Oehl

17.0(C) 17.1(C) 15.5(C) 4.0(R) 24.4(C) 15.2(C) 8.6(R)

A1–AlgodãodeJandaíra,PB;A2–Esperanc¸a,PB;A3–Ibaretama,CE;A4–Juazeirinho,PB;A5–Monteiro,PB;A6–Natuba,PB;A7–Poc¸inhos,PB.

FOi=ni/N,whereniisthenumberoftimesanAMFspecieswasobservedandNisthetotalnumberofAMFsporesobservedineachsite.R,rare

(FO<10%);C,common(10≤FO≤30%).43

ShanonandSimpsonindexes.Thetwoaxesexplained83.42%

ofthesamples’variation.

Discussion

Ourresultsprovidedevidencethat AMFare commoninM.

tenuifloraroots and rhizosphere, supporting ourhypothesis thatM.tenuiflorarhizospherehashighAMFsporeabundance

androotcolonization.However,AMFspecieswere

quantita-tivelyvariableamongthestudiedsites.Melloetal.46_reported

low values ofspore abundance, <1sporeg−1 soil, and root

colonization,<10%,intherhizosphereofnativeplantsfrom

Braziliansemi-aridregion,asAspidospermapyrifolium,Bromelia

sp.,Myracrodruonurundeuva, Tabebuiaimpetiginosa,and Zizy-phus joazeiro. Contrarily, crop host plants, such as maize

and sorghum,usually havehigh sporulation(>5sporesg−1

soil)andhighrootcolonizationvalues(approximately40%).47

Thus,ourresultssuggestthatM.tenuiflorahaveagoodlevel

of promiscuity as a host plant, presenting high values of

sporulation and mycorrhizalcolonization independentlyof

thestudiedsite.Inadditiontothevariabilityfoundinspore

abundanceandrootcolonizationforallstudiedsites,wealso

observedasignificantvariationinthecontentofvesiclesand

arbuscules,whichprobablyindicatesdifferentphysiological

and/orphenological mechanismsofthe symbiosisbetween

thehostplantandthefungiamongsites(Unpublisheddata).

Thedifferencesinsporeabundanceandrootcolonization

amongsites are inagreement withprevious work15,48 _that

reportedvariabilityinsporeabundanceduringthedryseason

inBraziliansemiaridregionforAMFspeciesfrom

45 40 35 30 25 20 15 10 5 0 A1 b d bc cd c c cd a a d b b a b A2 A3 A4 A5 A6 A7

Number of spores (g soil) Root colonization (%)

Fig.2–AMFsporeabundance,givenasnumberofspores g−1soil,andpercentageofrootcolonization(mean±SE,

n=40)intherhizosphereofM.tenuiflora.Differentletters representstatisticallysignificantdifferences(p<0.05) amongsites,afterone-wayANOVAandLSDtestforoverall comparisons.

periodofgreatestAMFsporeproduction,becausesoilwater

availabilityplaysanimportantroleintheAMF-hostplant

rela-tionship,namelyintermsofthecompositionandfunctioning.

Also,dataavailableintheliteraturefromelsewhereshowed

thatsporeabundancemightvaryfrom0to13sporesg−1soil

androotcolonizationrangesfrom27.7to45.7%inother

semi-aridandaridregions.13,49

Our results for total AMF species richness differ from

the ones presented by Silva et al.,15 _{which found that}

AMF total species richness might be larger than 40 AMF

species.Thisdissimilarityinresultsmaybeduetosoil

site-specificcharacteristics, aswell asrhizosphere peculiarities

that differ among sites that might determine the number

of AMF species present, and consequently, the number of

AMFspeciesdetected.49_{However,ourresultsaresimilarto}

recentlypublisheddata fromsemiaridand aridareas

else-where,whichshowedtotalrichness tovarybetween3and

32AMFspecies.16,50

TherewasastatisticallysignificantdifferenceinAMF

diver-sity and dominanceamongsites.A4was thesite withthe

greatest diversity (2.64) and the highest dominance index

(0.91). Other studies carried out in the Brazilian semiarid

region foundsimilarresults.15,51 _{Aspointedout above,soil}

propertiesmayhavemoreinfluencethanthehostplanton

theAMFcommunity,15,47,52_{becausesoilpH,wateravailability,}

phosphorousandnitrogencontentsaredeterminantfactorsin

thecompositionandfunctioningoftheAMF-hostplant

rela-tionship.Ourstudyprovidesevidencethatthesoilproperties,

suchassoilpH,totalnitrogenandphosphorousavailable,are

keyaspectsontheAMFcommunitystructureintheBrazilian

semiaridregion.

Species ofAcaulospora,Claroideoglomus,Dentiscutata,

Fun-neliformis,Gigaspora,RhizoglomusandScutellosporawereamong

the identified taxa.These genera are common insemiarid

sites,13,15,53_{andacidsoilswithlowphosphorousavailability.}54

Previous studies have shown the presence of these AMF

speciesassociatedwithM.tenuiflora.9,12,13_{Moststudieshave}

shownacertainconstancyintheAMFgeneraassociatedwith

this plantspecies, like Acaulospora, Archaeospora, Gigaspora,

Glomus,andScutellospora,14,15_{buttherearenoreportsof}

dom-inantAMFgenusintheM.tenuiflorarhizosphere.46_Ourresults

alsosupportthelackofdominanceofagivenAMFgenusor

speciesassociatedwithM. tenuiflorarhizosphere.Moreover,

thehighabundanceofrepresentativesfromtheOrder

Gigas-poralesfoundinourstudy,mightgivesomesupporttothe

hypothesis proposed by Goto et al.36 _{and Marinho et al.,}55

whichpointsoutthatBrazilisthediversificationand

disper-sioncenterofspeciesfromGigasporales.

1.0

0.8

0.6

Total organic carbon

Axis 2 (14.81%) AMF species richness Shanon index Simpson index Axis 1 (68.61%)

Total nitrogen Soil pH

Available phosphorous 0.4 –0.2 0.2 –0.8 –0.6 –0.4 –0.2 0.2 0.4 0.6 0.8 1.0 A4 A1 A3 A2 A5 A7 A6 –0.4 –0.6 –0.8

Fig.3–PCAscoreplotofsoilpropertiesandAMFcommunitystructure,hererepresentedbytheecologicalindexes calculated(speciesrichness,ShanonindexandSimpsonindex).A1–AlgodãodeJandaíra,PB;A2–Esperanc¸a,PB;A3– Ibaretama,CE;A4–Juazeirinho,PB;A5–Monteiro,PB;A6–Natuba,PB;A7–Poc¸inhos,PB.Pointsrepresentsamplesfrom eachplotbystudiedsites.

Soil properties differed among all studied sites. These

resultssupportourhypothesisthatsoilpropertiesare

impor-tant factors influencing the AMF community in the M.

tenuiflorarhizosphere.AccordinglytoOehletal.35_andCarneiro

etal.,49_{soilpH,availablephosphorous,andothersoil}

prop-ertiescanchangeAMFcommunitycomposition, increasing

the frequency of mutualists from genera Acaulospora,

Fun-neliformis,Gigaspora and Scutellospora.There wasa negative

correlationbetweensoilpH,totalnitrogenandphosphorous

availabilityandthedifferentecologicalindicescalculatedfor

eachsite(Fig.3).Ourresultsareinagreementwithprevious

workcarriedoutin16locationsacrossEurope,47_whichfound

that different soil types contained different AMF species.

InSwitzerland,astudy analyzing 154different agricultural

soilsamplesreportedthattheabundanceofsomeAMFtaxa

wasalsorelatedwithsoilvariables.52_{Morerecently,astudy}

performed along an environmental gradient in the

Brazil-iansemiaridregionfoundastrongcorrelationbetweensoil

attributesandAMFcommunitycomposition,concludingthat

soilpropertiesarekeyfactorsdeterminingAMFcommunity

structureinalocalscale,eventhoughsitesaregeographically

closetoeachother’s.15

In conclusion, our results showed that (1) AMF species

exhibithighsporulationduringthedryseason,(2)andthat

M. tenuiflorais a common hostplant, which points out its

importance in the biome it inhabits and its potential use

in reforestation programs in the Caatinga degraded areas.

However,furtherresearchisneededtounraveltheeffectof

AMFinoculationinthenativeplants,M.tenuiflorainthis

par-ticular case, growing in different soil conditions and with

differentAMFcommunitiesbeforeestablishhabitat

restora-tionmeasures.DespitenodominantAMFspecieswasfound

inM.tenuiflorarhizosphere,rare andcommon AMFspecies

accordinglytoZhang’sclassification43_{weredescribed.Based}

ontheseresults,onecanassumethatthisnativeplantspecies

doesnotbenefitanyAMFparticulargenusandhighlightsits

potentialinAMFcommunities’restorationindegradedsoils.

Furtherwork isneededtounderstandwhetherthisdiverse

AMFcommunityhasapositivedifferentialeffectinincreasing

nativeplantgrowth,resistanceortolerancetorootpathogens

intheBraziliansemiaridregion.56,57

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgements

SpecialthankstoJoana Costaforvaluable discussionsand

checking of English grammar. Two anonymous reviewers

providehelpfulcomments,whichgreatlyimprovedaprevious

versionofthemanuscript.

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