68InteractiveeffectsofNandPongrowthnutrientallocat

AquaticBotany64(1999)369–380InteractiveeffectsofNandPongrowth,nutrientallocationandNH4uptakekineticsbyPhragmitesaustralisJoséAntonioRomeroa,HansBrixb,FranciscoA.Com´ına;aDepartmentofEcology,UniversityofBarcelona,Diagonal645,08028Barcelona,SpainbDepartmentofPlantEcology,UniversityofAarhus,Nordlandsvej68,DK-8240Risskov,DenmarkAbstractTheinteractiveeffectsofthreelevelsofNH4–N(50,500and1000mmoll−1)andtwolevelsofphosphate(15and50mmoll−1)ongrowth,nutrientallocationandammoniumuptakekineticsbyPhragmitesaustralis(Cav.)Trin.exSteudelwerestudiedinhydroponiccultureinthelaboratory.Nitrogenlevelintherootsolutionsignificantlyaffectedtherelativegrowthrateoftheplants,theratebeingloweratlowN(0.026perday)thanatintermediate(0.035perday)andhighN(0.037perday),butphosphorusdidnotsignificantlyaffectgrowth.TheN:PratiointherootsolutionsignificantlyaffectedthegrowthratewhichwashighestatN:Pratiosbetween10and33onamolarbasis.NitrogenandphosphorusconcentrationintheplanttissuesgenerallyincreasedwithNlevelintherootsolution,butPlevelhadnoeffect.PlanttissueN:Pratios(onamolarbasis)variedbetween13.5inthestemsto28.0intheleavesandwereunaffectedbythetreatments.Am-moniumuptakekineticswereunaffectedbyNtreatment,butVmaxwassignificantlyaffectedbyPtreatmentaveraging(mean95%confidencelimits(CL))15144mmolg−1rootdryweighth−1inthelow-Ptreatmentand22970mmolg−1rootdryweighth−1inthehigh-Ptreatment.Theoverallmean(95%CL)NH4–Nuptakekineticparameterswere:Vmax=19020mmolg−1rootdryweighth−1;K1=2=21.81.8mmoll−1,andCmin=1.20.2mmoll−1.Mean(SD)rootres-pirationratewas7222mmolCO2g−1dryweighth−1andwasunaffectedbythetreatments.TheresultsofthestudysupportthegeneralhypothesisthatP.australisiswell-adaptedforgrowthinnutrient-richhabitats.However,P.australisisabletoacclimatetolownutrientavailabilitybyincreasingtheaffinityforammoniumuptake.©1999ElsevierScienceB.V.Allrightsreserved.Keywords:Relativegrowthrate;Nutrientallocation;Rootrespiration;Die-back;Acclimation;N:Pratio;PhragmitesaustralisCorrespondingauthor.Tel.:[phone];fax:[phone]E-mailaddress:[e-mail](F.A.Com´ın)0304-3770/99/$–seefrontmatter©1999ElsevierScienceB.V.Allrightsreserved.PII:S0304-3770(99)00064-9370J.A.Romeroetal./AquaticBotany64(1999)369–3801.IntroductionThecommonreed(Phragmitesaustralis(Cav.)Trin.exSteudel)growsinawiderangeofhabitats,includingsaltmarshes,thelittoralzoneoflakes,fens,bogs,andevenrelativelydryareas,ifcompetitionfromotherspeciesislow(Haslam,1970).Although,P.australiscommonlycanbefoundinoligotrophichabitats,itgrowsbestatfertilesites(Hockingetal.,1983).Itisthepreferredspeciesinconstructedwetlandsheavilyloadedwithdomesticsewageorsewagesludgeandgenerallygrowsprolificallyinthesesystems(Hofmann,1990;Brix,1994;KadlecandKnight,1996;Vymazaletal.,1998).Thus,P.australisisaspecieswithabroadecologicalamplitudeandabletoacclimatetoawiderangeofgrowthconditions.Thedie-backofP.australisrecordedinrecentyearsinmanyEuropeanwetlandshasfrequentlybeenassociatedwitheutrophication(Ostendorp,1989;ˇC´ıžková-Konˇcalováetal.,1992).Ithasbeenshownexperimentallythatextremelyhighnutrientlevels(Dykyjová,1978)andhighloadingsofsludge,particularlyanaerobicdigestedsludge(Hofmann,1986),inhibitgrowthandinducetypicalstresssymptomssuchasstuntedgrowthandchloroticleavesinP.australis.However,thisisprobablynotaneffectofthehighnutrientlev-elsperse,butratheraneffectofhighsaltconcentrationsorreducingsoilconditionsgeneratinghighconcentrationsoftoxiccompoundssuchasorganicacidsandsulphidesinthesediment(Armstrongetal.,1996;ˇC´ıžkováetal.,1999).Eutrophicationhasalsobeenreportedtostimulatethedie-backprocessviaaccumulationoflitterandalloge-nousorganicmatter(vanderPutten,1997;Brix,1999),aswellasviadisturbedcarbo-hydrateandnutrientcyclingintheplant(KühlandKohl,1992;ˇC´ıžková-Konˇcalováetal.,1992;KubinandMelzer,1996).Itis,however,possiblethatanimbalancedsupplyofthemainnutrients,NandP,willadverselyaffectthemetabolismandhencethegrowthofP.australis.Manystudieshavedealtwiththeeffectsofeutrophicationongrowth(Rintanen,1996;KubinandMelzer,1997),mechanicalstrength(Ostendorp,1995),carbohydratedynamics(Kubinetal.,1993;KubinandMelzer,1996),decomposition(Andersen,1978),anatomyandgasexchangeproperties(Votrubovaetal.,1997)ofP.australis,buttoourknowl-edge,nostudieshavebeenconductedonthepossibleinteractiveeffectsofnitrogenandphosphorusavailabilityongrowthandthephysiologyofnutrientuptake.Inthisstudy,weinvestigatedtheinteractiveeffectsonammoniumandphosphorusavailabilityongrowth,biomass,nutrientallocationandammoniumuptakekineticsbyP.australisinordertoes-Table1ConcentrationsofNH4–NandPO4–P(mmoll−1)andthecorrespondingN:PratiosintherootsolutionsinthegrowthexperimentswithP.australisTreatmentNH4–N(mmoll−1)PO4–P(mmoll−1)N:PratioLowN;lowP150153.3LowN;highP150501IntermediateN;lowP5001533IntermediateN;highP5005010HighN;lowP10001567HighN;highP10005020J.A.Romeroetal./AquaticBotany64(1999)369–380371tablishtowhatextenttheplantrespondsto,andacclimatesto,thenutrientavailabilityinthesurroundings,andinordertoelucidatehowimbalancedNandPsuppliesaffecttheplant.Weh