·2014-Actual evapotranspiration and crop coefficients for five year old bamboo (ELSVIER)

ContentslistsavailableatScienceDirect

Agricultural

Water

Management

j o ur na l h o me pa g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t

Actual

evapotranspiration

and

crop

coefficients

for

five

species

of

three-year-old

bamboo

plants

under

a

tropical

climate

Julien

Piouceau

_,

_Frédéric

_Panfili

_,

_Grégory

_Bois

_,

_Matthieu

_Anastase

_,

Laurent

Dufossé

_,

_Véronique

_Arfi

a_{PhytoremS.A.,sited’Areva,chemindel’autodrome,F-13140Miramas,France}

b_{UniversitédeLaRéunion,LaboratoiredeChimiedesSubstancesNaturellesetdesSciencesdesAliments,siteESIROIDépartementAgroalimentaire,2rue} JosephWetzell,F-97490Sainte-Clotilde,France

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received29August2013

Receivedinrevisedform28January2014 Accepted4February2014

Keywords:

Bamboo Lysimeter Evapotranspiration Cropcoefficient Biomass Tropicalclimate

a

b

s

t

r

a

c

t

Overthelastdecade,bambooplantationshavestartedtobeusedasvegetationfiltersforwastewater treatment.Thistreatmentsystemcanbeusefulinreducingwastewaterdischargeintotheenvironment, thuscontributingtothepreservationofwaterresourcesbyusingtheplantation’sevapotranspirationto reducetherateofwaterinfiltration.Theevapotranspirationratesofthebamboospeciesusedis there-foreanimportantfactor.Theactualevapotranspiration(ET)andthecropcoefficients(kc)forthefive tropicalandtemperatespeciesofthree-year-oldbambooplants,i.e.Bambusaoldhamii,Bambusa mul-tiplex,Bambusavulgaris,PhyllostachysaureaandPseudosasajaponica,werestudiedinlysimetersfora periodofmorethanoneyearunderatropicalclimate.TheaverageETratesforthebamboospecies studiedrangedfrom4to7mmday−1_{withmaximumvaluesofbetween10.7and17.1mmday}−1_during thewetseason,andanaveragekcof1.1to1.9.TheETwascorrelatedtoweatherparameters,especially minimumtemperatures.ThedifferencesinETratesbetweenthebamboospeciescanbeexplainedby morphologicalparameters,inparticularthetotalabovegroundbiomass.Amongthefivebamboospecies studied,B.oldhamiihadthehighestETrateandproducedthemostbiomass.Incomparisonwithother high-biomass-producingplants,theevaporationratesforyoungbambooplantsweresimilartothosefor willowandpoplarvegetationfilters.

©2014ElsevierB.V.Allrightsreserved.

1. Introduction

Waterresourcesconservationisanimportantissuetoday.The eutrophicationprocessinwaterespeciallyisaworldwideconcern (Smith,2009;Smithetal.,1999).Naturalwastewatertreatment systemsusingphytoremediationprincipleshavebeendeveloped inordertoprovideausefulalternativetomoreconventional waste-watertreatmentsystems,particularlyin ruralorisolatedareas. Mostofthesesystemsinvolveconstructedwetlandusingaquatic plants (Vymazal, 2011).Anothertype of systemusesterrestrial plantssuchaspoplar,willowand–morerecently–bamboo,where theplantsareusedasvegetationfilters(Arfietal.,2009;Aronsson andPerttu, 2001;Perttu and Kowalik, 1997;Singhet al.,2008; Yadavetal.,2010).

∗ _{Correspondingauthorat:PhytoremS.A.,sited’Areva,chemindel’autodrome,}

F-13140Miramas,France.Tel.:+33486260805;fax:+33490581578.

E-mailaddresses:[email protected],

[email protected](J.Piouceau).

Althoughbambooisstillrarelyusedforphytoremediation pur-poses(waterorsoiltreatments),itneverthelesssharesanumber ofinterestingcharacteristicswithotherplantsusedin phytoreme-diation.Amongtheseisbamboo’sapparenttolerancetopollutants suchastracemetals(Collinetal.,2013;Guietal.,2011;Shukla etal.,2011),andtotheexcessivedosesofnutrientsthatcanbe con-tainedinwastewater(Piouceauetal.,2014).Bambooalsodevelops adenserootsystemwithaprofusionoffinerootsandhairroots (Christantyetal.,1996)thatfavorsthehostingofmicroorganisms andimprovestherhizodegradationoforganicmattercontainedin wastewater(LichtandIsebrands,2005;McCutcheonandSchnoor, 2003).Lastly,giantbamboospeciesareamongthemostproductive terrestrialplantsintheworld.Theabovegroundbiomassyieldof matureplantationscanreach25and47tha−1_yr−1_under temper-ateandtropicalclimates,respectively(Scurlocketal.,2000).These high-yieldplants areinterestingfor wastewatertreatment pur-posesbecausetheycanhelppreservethequalityofwaterresources bylimitingtheeutrophicationphenomenonintwocomplementary ways.First,bystoringlargeamountsofnitrogenandphosphorous (themainelementsinvolvedineutrophication)intheirbiomass:a

http://dx.doi.org/10.1016/j.agwat.2014.02.004

maturebambooplantationcanstore131to619kgha−1_ofnitrogen and17to97kgha−1_{ofphosphorousinitsabovegroundbiomass} (KleinhenzandMidmore,2001).Second,byslowingtheinfiltration ofwaterthroughtheirhighevapotranspirationrates;Kleinhenz andMidmore(2002)estimatedthattheETrateofamaturebamboo plantationcanrangebetween9and13mmday−1_{underatropical} climate.

Thedevelopmentofvegetationfiltersusingterrestrialplants hasbeenboostedbyregulatorypressuretoreduceorstopthe dis-chargeofanytreatedwaterintotheenvironment.Indeed,evenif thetreatedwatercomplieswithenvironmentalqualitystandards, itstillcontains smallamountsof nitrogenand phosphorusthat arepotentiallyharmfulforthewaterresources.Thisisparticularly trueforsensitiveareassuchasthelagoonsandstreamsonReunion Island(Chazottesetal.,2002;Naim,1993;Semple,1997;Tedetti etal.,2011),forwhichatargetofzerodischargeofanywaterinto theenvironmentneedstobeimplemented.Invegetationfilters,the wastewaterisdirectlyspreadovertheplantation’ssoilsurface.The treatedwastewaterisreleasedthroughpercolation,viatheroot zonetothewatertableandintotheatmospherethrough evapo-transpiration.Thiskindofsystemcanbedesignedandmanagedto avoidanydischargeofanywaterintothewatertable.Todothis, theevapotranspiration(ET)ratesoftheplantspeciesusedmustbe accuratelyknowntosettheappropriatewastewatervolumetobe spreadontheplantation.

Somestudieswerecarriedoutonthetranspirationofvarious bamboospeciesusingthesap-flowmethod(Diericketal.,2010; Komatsuetal.,2010,2012;Kumeetal.,2010),butmostofthese didnottakeintoaccounttheevaporationviathesoil.Furthermore, theywereconductedinnon-irrigatedconditionssothe experimen-talmethoddidnotallowtheplants’fulltranspirationpotential tobequantified.Anotherexperimentalmethoduseslysimeters (Aboukhaledetal.,1982).Thelysimetermethodiswell-adapted tomeasuringtheET,thatistosayboththeplanttranspirationand thesoilevaporationaremeasuredinfieldconditions.Thismethod alsoallowsthecropcoefficient(kc)tobecalculated.Thekc ofa plantspeciesistheratiobetweentheETrateoftheplantstudied andthereferenceevapotranspiration(ET0)(Allenetal.,1998).The lysimetermethodhasbeensuccessfullyusedtostudytheETand kcofsomehigh-biomass-producingplantssuchaspoplarand wil-low(Guidietal.,2008;PauliukonisandSchneider,2001;Pistocchi etal.,2009).Toourknowledge,thereiscurrentlyalackofdata ontheevapotranspirationratesofbambooandothergiantgrasses (e.g.switchgrass,Miscanthussp.orArundodonax).Consequently, theaimofourstudywastodeterminetheETratesandkcof sev-eralbamboospeciesandtocomparetheminordertoselectthe mostappropriatespeciesforvegetationfilters(i.e.thespecieswith thehighestETrate).Tothisend,weputinplacepercolation-type lysimeters(Allenetal.,2011)tomeasureETratesoveraperiodof morethanoneyear.Morphologicalparameters,suchasleafarea andtotalabovegroundbiomass,werealsomeasuredtoaccountfor differencesinETratesbetweenspecies.

2. Materialsandmethods

2.1. Experimentalconditions

Theexperiment wasconducted over one year,from August 20th,2008toOctober30th,2009(436days),onReunionIsland,an overseasFrenchdepartmentinthesouth-westIndianOcean.The experimentalsitewaslocatedatLeGuillaume,SaintPaul(21◦03 48S;55◦1924E)atanelevationof1043m.

Fifteenpercolation-typelysimetersweresetupatthe experi-mentalsite(Fig.1).Thelysimetersconsistedof1.2m3_plastictanks (1.00mdeep,1.00×1.20minarea).Thelysimeterswereplaced

Fig.1.Lysimetersetupattheexperimentsite.

70cmaparttoprotecttheirsidesfromdirectsunlight.Thesidesof thelysimeterswerealsoinsulatedwithapolypropylenemembrane topreventheating.

Thelysimeterswerefilledwith20cmofgravelatthebottomasa drainagelayer.Ageotextile(bidimgreen®,TenCateGeosynthetics, France)waslaidontopofthegravelbeforethetankswerefilled witha3:1:1(v:v:v)mixtureofsoil,scoriaandsugarcanefibers,the characteristicsofwhicharelistedinTable1.

The lysimeters were planted with five different species of three-year-oldbambooplants:threetropicalspecies(pachymorph rhizome;Stapleton(1998):BambusaoldhamiiMunro(BO), Bam-busamultiplex(Lour.)Raeusch(BGG)andBambusavulgarisSchrad. (BVV))andtwotemperatespecies(leptomorphrhizome;Stapleton (1998):PhyllostachysaureaRivière&C.Rivière(PA)andPseudosasa japonica(Steud.)Makino(PJ)).Thelysimeterswerearrangedina completelyrandomizeddesignbasedonthefactorspecies(five lev-els)withthreereplicatesperspecies.Thebamboospecieswere plantedin thelysimeters’ reconstitutedsoil in May 2008,four monthsbeforethestartoftheexperiment,toallowforthe bam-boo’sproperrootingandanaturalcompactionofthesoil.

Table1

Averagelysimetersoilpropertiesafterbambooplantation.

Particledensity(gcm−3_{) 2.8}

Bulkdensity(gcm−3_{) 0.6}

Soilwaterholdingcapacity(mm) 210

pHwater 6.3

EC(mScm−1_{) 0.3}

Totalnitrogen(gkg−1_{) 2.7}

Totalorganiccarbon(g.100gdrysoil) 3.1 PhosphorusOlsen-Dabin(gkg−1_{) 0.3}

CEC(meq.100g) 14.1

Eachlysimeter wasirrigated withanautomaticdrip system (NetafimTM_{, Israel) using four drippers. Two spikes delivering} 4×lh−1_{perspikewereinsertedintothesoilforeachdripper,} giv-ingatotalflowof32×lh−1_{foreachlysimeter.Thelysimeterswere} irrigatedonceaweekwithtapwater,withatwice-weeklyaddition ofafertilizersolutioncomprisingacommercialfertilizer(20:20:20 NPKsoluplantduclos®,DuclosInternational,France)andatrace elementsolution(OligoDrip25Fe,Duclosinternational,France) dilutedwithtapwater.Thefertilizersolutionwasdilutedin-line usingameteringpump(DI16,DosatronInternational,France)with theresultingnutrientsolutiongoingtothedripirrigationsystem. Thedilutionwas1%inthedryseason(MaytoOctober)and1.6% inthewetseason(NovembertoApril).The solution concentra-tionwas300mgl−1_{ofnitrogen(N),300mgl}−1_{ofphosphorus(P)} and300mgl−1_{ofpotassium(K)(electricconductivity1.3mScm}−1₎ duringthedryseasonand480mgl−1_{ofN,PandK(1.8mScm}−1_)in thewetseason.Theapplicationofnutrientswasdesignedtomake fertilizationanon-limitingfactorinthebamboo’sgrowth;during theexperiment,atotalof672.1gofN,PandKwereappliedtoeach lysimeter,representingatotalof5.6tha−1_yr−1_ofnitrogen, phos-phorusandpotassium.Theaveragedailyheightofwater(tapwater orfertilizersolution)addedtothelysimeterswas8.9mmday−1_in thedryseason,and22.2mmday−1_{inthewetseason.Thevolumeof} irrigationwatersuppliedtothelysimeterwasadjustedaccording tothesoil’swater-holdingcapacity,210mm.Thissupplyofwater allowedthesoil’smoisturecontenttobemaintainedclosetofield capacitythroughouttheexperiment.

Afaucetatthebaseofeachlysimeterwasconnectedto20-l plasticcantocollectthedrainagewater.

2.2. Climaticparametersmeasurements

Theairtemperatureandrelativehumidityweremeasuredon theexperimentalsiteeveryhourusingdataloggers(EL-USB-2, Las-carselectronics,UK)(Fig.2aandb).Threedataloggersweresetup onthreelysimeterschosenatrandom.

Therainfall heightwas measuredbythe site’s meteorologi-calstationand referenceevapotranspiration(ET0)wasobtained from the Météo-France (French meteorological agency) mete-orological station at Bois de Nèfles on Reunion Island, at 7.656kmfromourexperimentalsite.TheET0wasdeterminedby Météo-France(Frenchmeteorologicalagency)usingtheFAO-56 Penman–Monteithequation(Allenetal.,1998),withdaily mete-orologicaldata(includingairtemperature,relativehumidity,wind speedandsolarradiation)obtainedusinganautomaticweather station.

2.3. Determinationofactualevapotranspirationandcrop coefficients

Ten-daymeanETforeachbamboospecieswascalculatedusing thesimplifiedwaterbalanceequation(RanaandKaterji,2000)(Eq. (1)below),assumingthatthesoil’swatercontentwaskeptatfield capacitythroughouttheexperiment(Guidietal.,2008;Pistocchi etal.,2009):

ET=I+R−D (1)

where Iistheamountof waterprovided byirrigation(mm), R therainfall height(mm) and D thedrainage height(mm). The drainagevolumesofeachlysimeterweremeasuredeverytwodays byweighingthe20-lplasticcanswitha20g-precisionspringscale (HS-50,Voltcraft®,Germany).Thedrainageheightwasobtainedby dividingthedrainagevolumesbythesurfaceareaofthelysimeters (i.e.1.2m2_).

Fig.2.Ten-daytemperatures(T)andrainfall(a)andrelativehumidity(RH)(b) dur-ingtheexperimentfromAugust2008toOctober2009;DS1:firstdryseason;WS: wetseason;DS2:seconddryseason.

Themean10-daycropcoefficients(kc)werecalculatedusing thefollowingEq.(2)(Allenetal.,1998):

kc= _ETET 0

(2)

whereETistheactualevapotranspiration(mm),andET0the refer-enceevapotranspiration(mm).

2.4. Growthmeasurementsandplantsampling

Atthebeginning andend of theexperiment, thenumberof culmswascountedineachlysimeter,theirheightmeasuredwith atapemeasureandtheirbasaldiametersmeasuredwithadigital caliperatthemiddleofthefirstinternode.Theinitialaboveground freshbiomassforeachbamboospecieswascalculatedfromthe basaldiametersofculmsusingallometricequationsestablishedby Piouceauetal.(2014).Attheendoftheexperiment,alltheculms ineachlysimeterwerecut.Thetotalabovegroundfreshbiomass, total freshleafmass and freshculmmasswasweighed witha 0.1g-precisionscale(Kern&SohnGmbH,Germany).

2.5. Leafareameasurements

AdobeIllustratorCS4software(AdobeSystemsInc.,USA).The spe-cificleafarea(SLA),i.e.leafareapermassunit,wascalculatedand thetotalleafareaperclumpwasdeducedbymultiplyingthe aver-agespecificleafareaofthesub-samplebythetotalfreshmassof leafperclump.

2.6. Statistics

WeusedanunivariaterepeatedANOVA(SPSSinc.,IBM,USA) tostudythedifferencein10-dayETorkcamongspecies. Spheric-itywascheckedwithMauchley’stest;whenthisassumptionwas rejectedtheGreenhouse-Geissercorrectionswereusedforthe F-statistics.TheLSDtestwasusedforpost-hocanalyses;p<0.05was chosentoidentifysignificantdifferencesbetweenspecies.

Aone-wayANOVA(SPSSinc.,IBM,USA)wasperformedtotest theeffectofthespeciesfactoronthenumberofculms,culm diam-eterand height,total abovegroundfreshbiomass,averagefresh culmmass,totalfreshleafmass,totalleafarea,andtotalannualET. Weperformedsquarerootorlogarithmictransformationsofdata tosatisfytheANOVAassumptions.TheLSDtestwasusedfor post-hocanalyses;p<0.05waschosentoidentifysignificantdifferences betweenspecies.

Weconductedatwo-tailedPearsoncorrelationanalysis(SPSS inc.,IBM,USA)todeterminetherelationshipsbetweenETrates ofeachspecies, ET0 andtheweathervariables:maximum tem-perature,averagetemperature,minimumtemperature,maximum relative humidity,averagerelative humidity, minimum relative humidityandET0.Anothertwo-tailedPearsoncorrelationanalysis (SPSSInc.,IBM,USA)wasperformedtodeterminetherelationships betweenthetotalannualETandmorphologicalparameters:total abovegroundfreshbiomass,totalfreshleafmassandtotalleafarea.

3. Results

3.1. Meteorologicalconditions

The temperature, relative humidity and 10-day rainfall are showninFig.2aandb.Theclimateistropicalwithawetseason betweenNovemberandApril,andadryseasonbetweenMayand October.Duringtheexperiment,thetemperaturesonsiteranged from6to38.8◦Cwithanaverageof18.6◦C,andarelative humid-ityfrom33.7%to99.3%,withanaverageof81%.Thetotalrainfall duringtheexperimentwas1373.9mm.

Ourexperimenttookplaceoverthreeseasons:twodry(DS1and DS2)fromAugusttoOctober2008andfromMaytoOctober2009, andonewet(WS),fromNovember2008toApril2009,thelatter correspondingtothemaingrowthperiodforbamboo.Thetwodry seasonswerecharacterizedbyaveragetemperaturesthatranged from13.5to21.5◦C,arelativehumidityof61.9%to90.4%,andlow rainfalls(only63mminDS2,thewetterofthetwodryseasons).The averagetemperatureduringDS2waslowerthaninDS1by2.8◦Cin Septemberand1.6◦CinOctober.Thewetseasonwascharacterized byaveragetemperaturesthatrangedfrom19.2to22.3◦C,arelative humidityof75.8%to90.4%andabundantrainfall(upto426.8mm inone10-dayperiod).

Theabundantrainfall recordedin the first10-day period of February2009wereduetoHurricaneGaëlthatcausedthethree temperaturedataloggerstobreakdown.Thedataloggerswere replacedonMarch10th2009.Consequently,temperatureswere notrecordedduringthisperiod.

3.2. Actualevapotranspirationandcropcoefficients

TheevapotranspirationpatternsareshowninFig.3.DuringDS1, thedifferentbamboo speciesshowed similarETrates untilthe endofOctober2008.DuringthisperiodtheETrangedfrom0.98

Aug -08

Sep -08

Oct-08

No v-08

De c-08

Jan-09

Feb -09

Mar-09 Apr-09 May-0 9

Jun-09

Jul-09 _Aug-09

Sep -09

Oct-09

No v-09

ET

(mm

.da

y

-1 )

0 2 4 6 8 10 12 14 16 18

BGG BO BVV PA PJ

ET0

Fig.3.Ten-dayaverageevapotranspiration(ET)forthespeciesBambusamultiplex

(BGG),Bambusaoldhamii(BO),Bambusavulgaris(BVV),Phyllostachysaurea(PA)and

Pseudosasajaponica(PJ);standarderror:±0.2.

to1.97mmday−1 _{forBGG,1.72to2.39mmday}−1_forPA,1.52to 3.09mmday−1_{forPJ,1.33to3.18mmday}−1 _{forBVV,and1.42to} 3.65mmday−1_{fortheBOspecies.}

AtthebeginningoftheWS,i.e.inNovember2008,theBGGand BOspeciesstarted toshowsignificantlydifferentpatternsofET ratescomparedtotheotherspecies.TheBGGspeciesshowedthe lowestETrateandBOthehighest.InDecember2008,theETrates increasedrapidlyandreachedtheirmaximumvaluesinJanuary 2009.DuringtheWS,theETratesshowedfourpeaksforallspecies. ThesamedifferencesbetweenspecieswereobservedasinDS1: theBGGspeciesshowedthelowestETrateandBOthehighest.The BVVandPAspeciesshowedsimilarETrates,and thePJspecies showedalower ETratethantheBVVandPA species.Between November2008andMarch2009,theETratesrangedfrom2.20 to12.34mmday−1_{forBGG,2.62to12.18mmday}−1_forBVV,2.69 to12.93mmday−1_{forPA,2.92to13.24mmday}−1_{forPJand3.83to} 17.17mmday−1_{fortheBOspecies.AttheendofMarch2009,the} irrigationsystembrokedownandconsequentlytheETrateswere notrecordeduntilMay.

DuringDS2,fromMay2009toOctober2009,theETratesof thespeciesdecreasedfrom29%to50%comparedtotheWS. How-ever,twopeaksofETwererecordedinthethird10-dayperiodof Juneandthesecond10-dayperiodofAugust.Onceagain,theET ratesoftheBGGandBOspecieswerelowerandhigher, respec-tively,thantheotherspecies.DuringDS2,theETrateswerehigher than duringDS1,ranging from1.19to6.12mmday−1 _{for BGG,} 1.67to8.46mmday−1 _{forPJ,2.46to9.87mmday}−1_forPA,2.73 to10.00mmday−1_{forBVV,and3.23to10.60mmday}−1_forBO.

Thecropcoefficientscloselyfollowedthesametrendasthe 10-dayET(Fig.4).DuringDS1,thedifferentbamboospeciesshowed similarkcvalues:from0.5to1.2and0.7to1.8fortheBGGandBO species,respectively.DuringtheWSthekcrangedfrom0.5to3.8 and1.0to5.7fortheBGGandBOspecies,respectively,and,during DS2,from0.5to3.0and1.3to5.2fortheBGGand BOspecies, respectively.

Theaveragekc wassignificantlydifferentfortheBGGandBO species(p<0.05)withvaluesof1.1and1.9,respectively(Table4). Theotherspeciesshowedaveragekcof1.4,1.5and1.6forthePJ, BVVandPAspecies,respectively.

Table2

Pearsoncorrelationcoefficients(r)forETrates(mmday−1_{)offivebamboospecies,referenceevapotranspiration(ET}

0)andweatherparameters.

Parameters BGG PA PJ BO BVV ET0

Maximumtemperature 0.27 0.1 0.24 0.25 0.1 0.60***

Averagetemperature 0.52*** _0.37* _0.48** _0.52*** _0.36* _0.66***

Minimumtemperature 0.72*** _0.63*** _0.66*** _0.74*** _0.61*** _0.57***

Maximumrelativehumidity 0.34* _{0.19 0.33}* _{0.32 0.16 0.32}*

Averagerelativehumidity 0.45** _0.50** _0.43** _0.49** _0.48** _0.05

Minimumrelativehumidity 0.39* _0.47** _0.37* _0.44** _0.46** _−0.04

ET0 0.44** 0.36* 0.44** 0.46** 0.34* 1

Bambusamultiplex(BGG),Bambusaoldhamii(BO),Bambusavulgaris(BVV),Phyllostachysaurea(PA)andPseudosasajaponica(PJ). Symbolsindicatesignificantcorrelation:*_p≤0.05;**_p≤0.01;***_p≤0.001.

minimumtemperature(r=0.72andr=0.74,respectively)thanthe temperate species, i.e., PA and PJ species (r=0.63 and r=0.66, respectively).Asexpected,theETratesofallthespecieswere cor-relatedwithaveragetemperatureandaveragerelativehumidity.

3.3. Bamboomorphologyandinfluenceontheactual evapotranspiration

Betweenthebeginningandendoftheexperiment,thenumber ofculms,culmdiameterandheight,andtheabovegroundfresh biomassyield increasedsignificantly (p<0.001). Thenumber of culmsincreasedbyafactorofbetween2.1and9.4fortheBOandPA species,respectively,theculmdiameterbyafactorofbetween1.3 and2.0forthePAandBGGspecies,respectively,theculmheightby afactorofbetween1.1and1.7forthePAandBGGspecies, respec-tively,andthebiomassyieldbyafactorofbetween5.4and18.1for theBOandBGGspecies,respectively.

Table3showsthatthespeciescanbegroupedbytheir morpho-logicalparameters.TheBOandBVVspeciesshowedfewer,taller culmswithlargerdiameterscomparedtotheotherspecies.In con-trast,thePJandBGGspeciesshowedagreaternumberofshorter culmswithsmallerdiametersthantheBOandBVVspecies.

TheannualtotalET(mmyear−1_{)correlateswiththetotalfresh} biomass(r=0.72,p<0.01),totalfreshleafmass(r=0.62,p<0.01) andtotalleafarea(r=0.61,p<0.05).TheBOspecies,whichshowed thehighesttotalETrate,alsoproducedthehighesttotal above-ground freshmass (withan averageof 39kg perclump),fresh leafmass(8.6kg)andtotalleafarea(117.6m2_{).Likewise,theBGG} species,whichshowedthelowestETrate,alsoproducedthelowest

Aug -08

Sep -08

Oct-08 Nov -08

Dec-08 Jan -09

Feb -09

Mar-09

Apr-09

May-0 9

Jun-09

Jul-09

Aug -09

Sep -09

Oct-09

Nov -09 kc

0 1 2 3 4 5 6

BGG BO BVV PA PJ

Fig.4.Ten-dayaveragecropcoefficients(kc)forthespecies:Bambusamultiplex

(BGG),Bambusaoldhamii(BO),Bambusavulgaris(BVV),Phyllostachysaurea(PA)and

Pseudosasajaponica(PJ).

biomass,freshleafmassandtotalleafarea(14.5kgperclump,3kg and30m2_{,respectively).}

4. Discussion

TheETratesvariedsignificantlythroughouttheyearwithahigh seasonalfactor(p<0.001).Allthespeciesshowedthesame tem-poralpattern,withthehighestETratesrecordedduringtheWS (October2008toApril2009),whenthetemperaturesandrainfall reachedtheirhighestlevelsoftheyear(Fig.2a).Asmentioned pre-viously,theWSisthemaingrowthperiodforbambooduringwhich newshootsemergefromthesoil(KleinhenzandMidmore,2001). ThehighETrates measuredduringthisseasoncan beascribed thereforetotheincreaseintotalnumberofshoots(Table3),which leadstoanincreaseinthetotalleafareaofthebambooclumpsand thereforetoanincreaseinET.Moreover,beforethisWS,theETrates werelowerandcloselyfollowedthereferenceevapotranspiration’s values(Fig.3).WealsonoticedthatETratesincreasedbetweenDS1 andDS2despitelowertemperaturesinDS2,whichindicatesthat theincreaseinbiomassduringtheWShadasignificanteffecton theincreaseinETinDS2.

DuringtheWS,theETratesshowedfourpeaksinDecember, JanuaryandMarch.Thesepeaksmaybeexplainedbytheincrease inaverageminimumtemperaturesatthecorrespondingperiods. Indeed,Table2showsthatETratescorrelatemorecloselywith minimumtemperaturethananyotherclimateparameter.Many studieshavedemonstratedthatanincreaseinETisclosely corre-latedwithanincreaseinminimumairtemperatures.Conversely, whenthetemperaturedropsbelowacertainvalue–dependingon thespecies–,thestomatalconductance ofleavesandtheroots’ hydraulic conductivity decrease (Jarvis, 1976; Mu et al., 2007), withaconsequentdecreaseinevapotranspiration.Airtemperature alsostronglycorrelateswithphotosynthesis(Gratanietal.,2008; Van Goethemet al.,2013), which alsoimpacts transpirationin bamboo(Agataetal.,1985).Thereareimportantdifferencesin opti-mumtemperaturerangesforphotosynthesisactivitydependingon thebamboospecies’ecologicaldistribution.Gratanietal.(2008) showedthatbambooofthegenusPhyllostachysfromtemperate climateshaveahighersensitivitytohightemperatureandthat, conversely,bambooofthegenusBambusafromtropicaland sub-tropicalclimateshaveahighersensitivitytolowtemperatures.For example,inthecaseofthegenusBambusa(i.e.tropicalspecies),the netphotosynthesisdecreasedmorethan50%whentemperatures dropped below 16.2◦C (Grataniet al., 2008).Thisphysiological behavioranditsconsequencesontheplant’stranspirationare con-sistentwithourstudy,inasmuch aswe havenoticeda better correlationbetweentheETratesandminimumtemperaturesin thetropicalspecies(BOandBGG)thaninthetemperatespecies (PAandPJ)(Table2).

Table3

Morphologicalparametersandabovegroundfreshbiomassforfivebamboospeciesatthebeginning(initial)andend(final)oftheexperiment.

Parameters BGG PA PJ BVV BO

Numberofculms Initial 72±12.8d 5.7±2.3a 36.7±2.8c 11.7±3ab 15.7±1.2b

Final 325.3±78.8c 54±8b 195±23c 25.7±3.5a 34.3±3.2ab

Culmdiameter(mm) Initial 3.3±0.1a 8.4±0.7bc 7.3±0.3b 11.1±1c 11.2±1c

Final 6.6±0.5a 11.3±0.8b 9.5±0.4b 22.0±2.8c 20.5±1.0c

Height(cm) Initial 115.1±5.4a 205.6±7.4b 170±13.3b 170.9±22.8b 170±13.3b

Final 201.4±13.9a 239.4±9.9ab 208.1±6.8a 259.3±26.9b 274.4±10.0b Abovegroundfresh

biomass(kg)

Initial* _{0.8±0.1a 1.4±0.3a 3.4±0.5b 2.9±1.1b 7.2±0.7c}

Final 14.5±0.3a 18.5±4.3ab 27.0±3.4b 24.6±2.0ab 39±0.1c Valuesaremeans±SE.Thevalueswithdifferentlettersindicatesignificantdifferencesbetweenthespecies(LSD,p<0.05).Bambusamultiplex(BGG),Phyllostachysaurea(PA),

Pseudosasajaponica(PJ),Bambusavulgaris(BVV)andBambusaoldhamii(BO).

* _{Estimatedbiomassusingallometricequation.}

Inadditiontothespecies’originalecologicalhabit,themain expla-nationforthedifferenceintheirETratesistheirdifferentbiomass yields,asshowninTables3and4.AsobservedfortheBOandBVV species,ahighbiomassisrelatedtoalargetotalleafarea,which implieshighET(Table4).Indeed,thesetwospeciesproducedtaller andlargerculmscomparedwiththethreeothers(Table3).

For all the species, the average ET ranged between 4 and 7mmday−1_{,withmaximum values during theWS of12.3 and} 17.18mmday−1_{, for the BGG and BO species, respectively. As} stressed in the introduction, few studies have dealt with the evapotranspirationofbamboospecies.Byusingthesap-flow mea-surementmethod,Diericketal.(2010)andKomatsuetal.(2010) reportedtranspiration rates of 1.4mmday−1 _{and ofbetween 3} and4mmday−1_{forBambusablumeanaSchult.f.andPhyllostachys} pubescensJ.Houz.,respectively. However,unlike in our experi-ment,thesoilevaporationinthesestudieswasnotincludedOnly KleinhenzandMidmore(2002)haveestimatedthe evapotranspi-rationof B.oldhamii(BO)withETratesrangingbetween9 and 13mmday−1_{.Thesevaluesareconsistentwiththosereportedin} ourexperiment.However,thelatterstudywascarriedoutusing smalllysimeters(pots)whichcangenerateexperimentalartifacts (RanaandKaterji,2000).Sincethereislittledataavailableonthe evapotranspirationofbambooandothergiantgrassesinliterature, ourresultscan becomparedonly withotherplantspecies.For sugarcanegrownonReunionIsland(thesiteofourownstudy), Chopartetal.(2007)reportedanaverageannualETofbetween 2.90and2.93mmday−1_{,withmaximumvaluesof3.50mmday}−1_. ThesevaluesarelowerthanthosefoundinourstudyoftheBGGand BOspecies;however,theycorrespondtoabiomassyieldforsugar caneof101tha−1_{offreshmass(Chopartetal.,2007),whereasthe} biomassyieldsinourstudyrangedbetween120and325tha−1_for theBGGandBOspecies,respectively,basedonthesurfaceareaof thelysimeter.Althoughwillowandpoplararetreesandtemperate plantspecies,they,likebambooareusedforwastewatertreatment (DimitriouandRosenqvist,2011).Indeed,theyhaveahighgrowth rate,biomassyieldsclosetothoseoftemperatebamboospecies(10 to15tha−1_yr−1 _{ofdrymass)andhighwateruptakes(Aronsson}

andBergstrom,2001;AronssonandPerttu,2011;Dimitriouand Aronsson,2011;PerttuandKowalik,1997).TheETvaluesforthe youngbambooplantsinourstudyaresimilartothosereported forwillowandpoplarusingthesamelysimetermethodasinour study.UnderaMediterraneanclimate,Guidietal.(2008)reported anaverageofbetween3.33and4.02mmday−1_{(withamaximumof} 15.46mmday−1_{)forpoplarandbetween3.47and6.65mmday}−1 (witha maximumof21.7mmday−1_{)forwillow,. Otherauthors} suchasPistocchietal.(2009)reportedsimilarETvaluesforpoplar andwillow.

ThekcvaluesfollowthesamepatternasETandrangedfrom 1.1 to1.9for theBGG andBO species, respectively.The values recordedinDS1,areconsistentwiththevaluesreportedbyPayet etal.(2009),whoreportedakcofbetween0.48and1.2formaize cropsonReunionIsland.Afterthedryseason,thekcvaluesrecorded forbamboowerehigherthanthemaximumaveragekcfoundin lit-eratureforcropswhichis1.25insugarcane(Allenetal.,1998).As expected,theaveragekcvaluesforthebambooinourstudyare closertothoseforwillowandpoplarinshortrotationcoppices. Guidietal.(2008)reportedakcofbetween0.33and5.30for wil-lowandbetween0.36and4.28forpoplar.Pistocchietal.(2009) reportedakcofbetween2.54and4.03forbothwillowandpoplar combined.

Theevapotranspirationratesfortheyoungbambooinourstudy appear high,raisingthe questionofpossibleexperimental arti-facts.Themainpotentialsourceoferrorwiththelysimetermethod canbedrasticdifferencesinatmosphericconditionsbetweenthe lysimeteranditsimmediatesurroundings;thisartifactisknown asthe“oasiseffect”(RanaandKaterji,2000).Ifthesurrounding areaconsistsofbareor poorlyvegetatedearth,netradiationin excessoflatentheatisconvertedintosensibleheatthatisadvected towardthelysimeter.Suchanetinputofenergyintothe lysime-tercanopyresultsinanoverestimationofET(RanaandKaterji, 2000).AsshownbyWegehenkelandGerke(2013),theoasiseffect inlysimeterssimilartothoseusedinourstudy(i.e.1m2_)can peri-odicallyoccurduringthesummerwhensolarradiationreachesits maximumintensity.Theoasiseffectcouldnotbetotallyexcluded

Table4

Morphologicalparametersandevapotranspirationratesattheendoftheexperimentafteroneyearofgrowthforfivebamboospecies.

Parameters BGG PA PJ BVV BO

Totalabovegroundfreshbiomass(kg) 14.5±0.3a 18.5±4.3ab 27.0±3.4b 24.6±2.0ab 39±0.1c Averagefreshculmmass(g) 45.5±5.6a 184.6±25.4c 95.9±8.3b 514.7±196.7cd 1149.7±102.2d

Totalfreshleafmass(kg) 3.0±0.8a 3.5±0.4a 5.0±0.5b 7.5±0.6c 8.6±0c

Totalleafarea(m2_{) 30.0±6.2a 35.6±3.7a 32.4±4.7a 81.3±4.6b 117.6±2.6c}

AverageET(mmday−1_{) 4±0.3a 5.5±0.3b 5.1±0.3b 5.4±0.3b 7±0.4c}

AverageET0(mmday−1) 3±0.1 3±0.1 3±0.1 3±0.1 3±0.1

kc 1.1±0.1a 1.6±0.2b 1.4±0.1b 1.5±0.2b 1.9±0.2c

AnnualtotalET(mmyr−1_{) 1270.1±67.1a 1605.5±42.7b 1605.8±98.5b 1704.1±27.9b 2218.7±30.8c}

inourcase,especiallyduringthewetseason,whichcorresponds totheperiodoftheyearwhensolarradiationisthehighest(Allen etal.,1998).However,comparingourresultswithotherstudies dealingwithevapotranspirationincropssuchasmaizeandsugar cane,andinpoplarandwillow,suggeststhatthedatareportedin ourstudyisreliable.Furthermore,inadditiontoprovidingnewdata onbamboospecies,ourstudycouldprovideusefulinformationfor optimizingthedesignforfutureexperimentsonETinbambooand othergiantgrasses

Lastly,theETvaluesmeasuredwerethoseforthree-year-old bamboothatistosayfornon-maturebamboo.Indeed,abamboo plantationreachesmaturityinfivetoeightyears,dependingonthe growthconditions.Thissuggeststhatforamaturebamboo plan-tationofgiantbamboosuchastheBOspecies,inwhichculmscan reach18minheightatmaturity(Castaneda-Mendozaetal.,2005), theETrateswouldbeevenhigher.

5. Conclusions

Theexperimentreportedhereis–toourknowledge–thefirst lysimeterexperimenttoinvestigatetheevapotranspirationrates ofdifferentspeciesofbamboo.Theresultsshowthatseasonsand minimumtemperaturesarethemainclimaticfactorsaffectingET. Asexpected,thedifferencesinETobservedbetweenspeciescan beexplainedbytheabovegroundbiomassyieldandthetotalleaf surfacearea,thetwomorphologicalparametersshowinga high correlationwithETrates.Amongthefivebamboospeciesused,B. oldhamiihadthehighestETrateandproducedthehighestamount ofbiomassduringtheexperiment.Incomparisonwith evapora-tionratesforotherhigh-biomass-producingplants,thoseforyoung bambooplantsaresimilartothoseforwillowandpoplarusedin shortrotationcoppices.Inconclusion,ourstudyprovidesuseful dataforthedesign and managementof vegetationfiltersusing bambooplantations.Thedatacouldalsobeusefulforthewater managementofcommercialbambooplantations.

Acknowledgments

TheresearchwasfundedbythefollowingFrenchgovernment institutions:“FondsUniqueInterministériel”,the“ConseilRégional de La Réunion”, the “Conseil Régional de Provence-Alpes-côte d’Azur”andthe“DépartementdeLaRéunion”aspartofits“Run InnovationII”project,supportedbytheReunionIslandcompetitive cluster“Qualitropic”andthe“PôleRisques”regionalcompetitive clusterinAix-en-Provence.

WewouldliketothankAlexandrePerrusotof“LaBambusaie duGuillaume”,ReunionIslandforsharinghisknowledgeof bam-boowithusandforallowingustocarryouttheexperimentathis bamboonursery.WewouldlikealsotothankMichelMonteville andSébastienSéverinfortheirhelpinbuildingtheexperiment andensuringthesmoothdailyrunningoftheirrigationsystem. SpecialthanksgotoLaurePrete,RemiHidouci,StéphaneMaillot, LaurentDeFondaumièreandCharles-LeeHoareaufortheirhelpin collectingfielddataandfortheirtechnicalsupport.

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