HORTSCIENCE 44(6):17041711. 2009.Nitrogen and Phosphorous Removalby Ornamental and Wetland Plantsin a Greenhouse RecirculationResearch SystemYan Chen1, Regina P. Bracy, and Allen D. OwingsLouisianaStateUniversityAgCenter, HammondResearchStation, 21549Old Covington Highway, Hammond, LA 70403Donald J. MerhautUniversity of California, Riverside, Department of Botany and PlantSciences, Riverside, CA 92521Additional index words. stormwater, water quality, bioltration, nitrateAbstract. Anutrientrecirculationsystem(NRS)wasusedtoassesstheabilityoffourornamental and three wetland plant species to remove nitrogen (N) and phosphorous (P)from stormwater runoff. The NRS was lled with a nutrient solution with total N and Pconcentrationsof11.3and3.1mgL1, respectively, tosimulatehighlevelsofnutrientcontaminations in stormwater. Nutrient removal abilities of herbaceous perennialornamental plants, canna(Canna generalisBailey)Australia, iris(IrispseudacorusL.) Golden Fleece, calla lily [Zantedeschia aethiopica (L.) Spreng], and dwarf papyrus(Cyperus haspan L.) were compared with those of wetland plants arrow arum [Peltandravirginica(L.)Schott],pickerelweed(PontederiacordataL.),andbulltonguearrowhead(Sagittaria lancifolia L.) in three experiments. Australia canna had the greatest waterconsumption, total biomass production, and aboveground N and P content followed bypickerelweed. GoldenFleeceirishadhighertissueNconcentrationsthancannabutmuch lower biomass production. Dwarf papyrus had similar total biomass as pickerel-weed but less shoot biomass. N and P removed from the NRS units planted with canna(98.7% N and 91.8% P) were higher than those planted with iris and arrow arum (31.6%and31.5%N, and38.5%and26.3%P, respectively). NRSunitsplantedwithdwarfpapyrus had similar nutrient recovery rate as pickerelweed, but much less total N and Pwere removed as a result of less water consumption. The NRS units planted with calla lilyhad lower nutrient removal than canna and pickerelweed. Our results suggest that cannais a promising ornamental species for stormwater mitigation, and harvesting theabovegroundbiomass of cannacaneffectivelyremoveNandPfromthetreatmentsystem. However,more research needsto bedone toevaluate factorsthat might affectplant performance in a oating bioltration system.Rapidpopulationgrowthandurbaniza-tion have raised concerns over stormwater run-offcontamination(BolundandHunhammer,1999; Walsh, 2000). Studies onwatershedsindicate that excess nutrients, specicallynitratenitrogen(NO3-N) andsolublereac-tive phosphorus (i.e., PO43), are foundinstormwater runoff exported from newlydeveloped urban areas (Dougherty et al.,2006; Steueret al., 1997). Thesepollutantsdegrade water quality and contribute toeutrophication or hypoxia of downstreamreceiving water (Dougherty et al., 2006). Toprotect water quality, the U.S. EnvironmentalProtection Agency (EPA) mandates maxi-mumallowable nitrate level in any dis-chargedwater tobe10mgL1(U.S. EPA,1986). Federal limits on phosphorus (P)concentrationsinfreshwaterhavenotbeenset, but EPArecommends that total phos-phates and total P levels not exceed 0.05 and0.1 mgL1, respectively (U.S. EPA, 1986).A variety of stormwater treatment technol-ogies such as constructed wetlands and reten-tionpondshavebeendevelopedinresponsetoincreasingregulatorypressures(Schaefer,1997; Schueler, 1992). However, water qual-ityissuessuchasnutrient accumulationanddeclined effectiveness have been found instormwater treatment structures (Hatt et al.,2009). Total nitrogen (N) and P concentrationsexceeding EPA guidelines were found inefuent fromretentionwetlands(Moustafa,1999; Serrano and DeLorenzo, 2008). There-fore, signicant N and P reductions arenecessary to improve waterquality before itis discharged into the ecosystem from storm-water retention structures.More recently, bioltration systems havebeen developed (Davis, 2005, 2007). Re-search to date suggests that planted retentionstructuressuchasplantedconstructedwet-landandraingardensaremoreefcient inremoving nutrients than unplanted structures(Henderson et al., 2007). Runoff diverted intoplantedstructures islteredthroughplantsfollowedbyvertical ltrationthroughsoilmedia. In laboratory-scale studies, plantedmesocosms (laboratory ecosystems that sim-ulate the structure and components of naturalecosystems) removed 63%to 77%Nand85%to94%Pfromsyntheticstormwater,whereas nutrient leaching was observed fromunplanted mesocosms (Henderson et al.,2007). In eld-scale studies, 50%to 70%nitrate reduction was accomplished by plant-ingPontederiacordatainsubsurfacecon-structed wetlands (DeBusk et al., 1995), and30% to 70% total P was removed by plantedstormwater ponds (Ou et al., 2006).However, plants are also a source ofnutrients in natural and constructed wetlands,andtheirroleinstormwatermitigationcanchangefromeffectiveremovaltoconsistentleaching(Hattetal., 2009). Rapidandsub-stantial decomposition and release of organicmatters were found in wetland plants after agrowing season. Odum and Heywood (1978)quantied that 40%to 50%biomass inPontederia cordata, Sagittaria lancifolia,and Peltandra virginica was released in 10 dand 70%to 80%biomass was released in 60 dto the water. Therefore, whole plant removalor harvesting shoot biomass is necessary, andinsomecasescritical, tomaintaintheper-formance of stormwater treatment structures.Cutting experiments suggest that removal ofshoot biomass in population managementapplications should be based on the availablecarbohydrate reserves in the rhizomatoustissues(Granelietal.,1992),anddecompo-sition models of several emergent aquaticperennialmacrophyteswereabletoidentifythe optimumtiming for shoot harvestingtominimizedetrimental inuenceonplantgrowth in subsequent seasons (Asaeda et al.,2008).Theuseofoatingwetlands(alsocalledoating islands) for stormwater mitigation isrelatively new, although oating bioltrationtechniques have been used to remove excessN in sh farms (Crab et al., 2007). Studies inawastewater treatment pondandalabora-tory-scaleconstructedwetlandsuggest thatthe use of oating systems increases mitiga-tioncapacityandprovidesefcientNandPremoval that is important for small-sizedtreatment structures in urban areas (Jayaweeraand Kasturiarachchi, 2004; Stewart et al.,2008). Inaddition, whenornamental plantsare used, oating systems add aesthetic valueto the treatment area and can mutually benetthe community and environment.Several obligate wetland plant speciessuchaspickerelweed(Pontederiacordata),arrowarum(Peltandravirginica),andbull-tongue arrowhead (Sagittaria lancifolia)Receivedforpublication29Apr.2009.Acceptedfor publication 9 July 2009.ThisresearchwasfundedbytheLakePontchar-trainFoundationandthe Louisiana AgriculturalExperiment Station. Plant material supplied byAG3, Inc.Trade names mentioned in this manuscript does notimply product endorsement by the authors and theirassociated institution.We thank Roger Rosendale and Joey Quebedeauxfor their technical assistance.1Towhomreprint requests shouldbeaddressed;e-mail yachen@agcenter.lsu.edu.1704 HORTSCIENCE VOL. 44(6) OCTOBER 2009havebeenstudiedfornutrientremovalabil-ities in wastewater treatments (DeBusk et al.,1995;Hadadetal.,2006;Readetal.,2008;Srivastava et al., 2008). However, fewstudieshavequantiedthenutrient removal abilityof wetlandspecies inaoatingsystem. Afewaquatic ornamental plants have beenstudied for wastewater (Belmont and Metcalfe,2003; Wolverton, 1990)andnurseryrunofftreatments (Polomski et al., 2007) in labora-tory-scalesubsurfaceconstructedwetlands.However, little data exist on nutrient removalandsurvivabilityoftheseornamentalplantsinoatingsystems (Miyazaki et al., 2004;Stewart et al., 2008).Inthis study, the followingornamentalplants were chosen as bioltration candidateplants: canna (Canna generalis Bailey)Australia, iris (Iris pseudacorus L.)Golden Fleece, calla lily [Zantedeschiaaethiopica(L.) Spreng], anddwarf papyus(Cyperus haspan L.).Besides their potentialof nutrient removal, theywerechosenalsobecause they are aesthetically attractive, ableto thrive in water, and are noninvasive. Threeobligate wetland species, pickerelweed,arrow arum, and bulltongue arrowhead, werechosen as reference species because theyhavebeenwidelyusedinwastewatertreat-ments. All of these plants are herbaceousperennials in areas above zone 5 of the USDAplant hardinesszonemap. Herbaceousper-ennials are desirable for oating systemsbecausetheir abovegroundbiomass canbeharvested by the end of a growing season toavoid releasing nutrients back into the water,and new growth will begin the next season tocontinue removing nutrients from the water.Ahydroponicnutrient recirculationsys-tem (NRS) was used for this study. The waterdynamics in this system are similar to reten-tion ponds or constructed wetlands thatreceive stormwater inows from time to time.The design of the plant growth containerof the NRS units simulates the growingconditionof aoatingsystem(Chenet al.,2008). Inaddition, the designof the NRSallows us to quantify the amounts of water andnutrients provided to individual units through-out the growing season and the nutrientsremaining in the system at the nal harvest.The objectives of this study were to quan-tify 1) the nutrient removal abilities of the fourornamental plant species andthreeobligatewetland species through aboveground bio-mass harvest; and2) thenutrient reductionintheNRSunitsplantedwiththesespeciesunderrelativelyhighlevelsoftotalNandPconcentrations found in stormwater treatmentstructures.Materials and MethodsThenutrient recirculationsystem. Threegreenhouse experiments were conducted in aNRS at the Louisiana State University Agri-cultural CenterHammondResearchStationfrom2005to2007. TheNRSwas anim-proved design based on a systembuilt atthe University of California, Riverside (Chenet al., 2008). The NRS includes six identicalunits, each of which was an independenthydroponicrecirculationunitproviding284Loftreatment solutiontosixplant growthcontainers.Theunitswereconsideredrepli-cations and the plant growth containers wereconsideredsubsamples intheexperimentaldesign of this research.Each plant growth container (53 cmwide 38cmlong 18cmdeep)hadapolyvinylchloride pipe nipple inserted into a bulkheadttingonthebottomof thecontainer as adepth controller to keep the water depthinsidethecontainerat10.6cm(Chenetal.,2008).Eachplantcontainerwascoveredbya piece of 1-cm thick marine plywood (39 56 cm) with one 14.6-cmdiameter round holein the center to hold a net pot. The plastic netpot wasroundandblackwith15.2-cmtopo.d. and 12-cm bottom o.d. (American Hydro-ponics, Arcata, CA). Inert hydroponic pottingmediumHydrotonexpandedclay(GeneralHydroponics USA, Sebastopol, CA) wasused in all experiments. The net pot wassupported by the plywood cover and sus-pended in the plant container. Plant rootswereallowedtogrowfromthenetpotintothe treatment solution trapped inside thecontainer. This container design simulatestheroot environment inaoatingbioltra-tionsystemwhereplantsareplantedinandsupportedbyaoatingplatform(i.e., poly-ethylene foam by Maryland Aquatic Nurser-ies,Jarrettsville,MD) withrootsgrowinginthe water.Besides the plant growth containers, eachunit consisted of a reservoir tank, a rell tank,an aeration system, and a pHmonitoringsystem. At theinitiationof anexperiment,the reservoir tank, rell tank, and plantgrowthcontainerswerelledwithaprede-termined solution to simulate polluted storm-water runoff. This solution was pumped fromthe reservoir tank into a supply line anddrippedthroughemitters tonet pots. Afterushing through the growing media, thesolutionowedthroughtubingbacktothereservoir tankfor another cycle. Therelltankwaslocatedonashelfhigherthanthereservoirtankandtreatment solutionaddedto the reservoir tank by gravity. The amountaddedwasmonitoredbyrecordingsolutionlevel insideatransparent plasticsight tubeaccompanied by a 0.65-m long ruler mountedalongthesideofeachrelltank. ReservoirtanksolutionpHwasmonitoredwithanin-line pHprobe (model 27001-70; Cole-ParmerInstrument Co., Vernon Hills, IL) connectedtoindividual pHcontrollers(AlphapH200;EutechInstruments Ltd., Singapore). Solu-tion pHwas adjusted daily by manuallyaddingbase(NaOH)oracid(H2SO4)tothereservoir tank to maintain solution pHat6.5 to avoid possible P precipitation underalkaline solution pHlevels. An air pump(AirTech40L;EvolutionAquaLtd. Wigan,Lancashire UK) supplied air to six air stones(Boyu Industries Co., Ltd., Guangdong,China) so that each aerated the solutionconstantlyinoneofthesixreservoirtanks.Themovementofairbubblesalsoprovidesagitation for constantly mixing the solution inthe reservoir tank.Allunitswerecontrolledsimultaneouslyby an irrigation controller (Sterling 8; Supe-rior Controls Inc., Valencia, CA). In allexperiments, units were programmed to oper-ate from6 AM to 8 PMand run for 40 min everyhour as a cycle. Ineachcycle, the motorvalvesundertherelltankswereturnedonfor therst 20mintoallowthereservoirtankstobelledwithtreatmentsolutiontothe designed level (98.3 L). Then the pumpsrun for 20 min to circulate the treatmentsolutionamongtheplant containers withina unit. Temperatures in the greenhouse wereset at 26.7 Cday/18.3 Cnight forall ex-periments. Actual temperaturesandrelativehumidityweremonitoredwithHOBOsen-sors(Onset Computer Corp., Bourne, MA).Theaveragemaximumandminimumdailytemperaturesandtheaveragemaximumandminimumdaily relative humidity over thetime during the three greenhouse experimentsare listed in Table 1. Less variation in green-house temperature andrelative humiditywasfound among the three experiments conductedfrom April to June compared with the exper-iment conducted fromOctober to December in2005.Plant preparation. Plantswerepreparedfortransplantfollowingthesameprocedurein all experiments. Australia canna, GoldenFleece iris, dwarf papyrus, arrow arum, pick-erelweed, and bulltongue arrowhead wereobtained fromCharleston Aquatic Nursery(Johns Island, SC) as liner plants in4-inchpots.Onarriving,plantswereremovedfromtheiroriginal pots, theirrootswerewashedfreeof mediaandcontrolled-releasefertil-izers, and then transplanted into 6-inch roundpots (1.43 L) in perlite. Calla lily bulbs wereobtained from Bourgondien & Son Inc.(VirginiaBeach,VA)andplantedin6-inchpots in perlite. Plants were grown undernaturalphotoperiod (lat.30N) for 2weeksand watered once a day with overhead sprin-klers. The2weeks of growinginaninertmedia without additional fertilization helpedTable1.Experimentdurations,averagedailymaximumandminimum temperatures,andaverage dailymaximumandminimumrelativehumidityinthegreenhousewiththenutrientrecirculationsystemduring three experiments (with Expt. 1 repeated).DurationAvg dailytemperature (C)Avg daily relativehumidity (%)Maximum Minimum Maximum MinimumExpt. 1 12 Apr. to 14 June 2005 29.0 15.4 89.5 39.23 Oct. to 7 Dec. 2005 23.6 8.6 68.1 24.5Expt. 2 4 Apr. to 12 June 2006 29.4 16.4 87.9 38.4Expt. 3 18 Apr. to 7 June 2007 30.9 16.4 90.4 41.1HORTSCIENCE VOL. 44(6) OCTOBER 2009 1705plants achieve relatively similar nutrientbackground. Plants were then removed fromtheir potsandrootswashedfreeof perlite.Withoffshoots removed, asinglestandofcanna, iris, arrowarum, pickerelweed, andbulltongue arrowhead and clumps of 10elongated stems of dwarf papyrus wereweighed and transplanted into net pots inHydrotonclay. Singlecallalilybulbswithside bulbs removed were weighed andplantedina separate net pot inHydrotonclay. Weusedplant freshweight toselectuniformplants andbulbs. After transplant,net pots were placed in the plant growthcontainers in NRS.Treatments. As a result of size limitationoftheNRSsystem,onlythreespecieswereevaluatedineachexperiment. Expt. 1wasconducted from 12 Apr. to 14 June 2005 andrepeatedfrom3Oct. to7Dec. 2005; thespecies evaluated were Australia canna,GoldenFleeceiris,andarrowarum.Expt.2was conductedfrom4Apr. to12June,2006,andthespeciesevaluatedweredwarfpapyrus, pickerelweed, and bulltongue arrow-head. Australia canna and pickerelweedshowed high nutrient removal ability in Expts.1 and 2, respectively, and therefore wereevaluated again along with calla lilyin Expt.3 from 18 Apr. to 7 June 2007.Ineachexperiment, atotal of 36plantswastransplantedintoNRSwhereeachspe-ciesoccupiedtwounits. Inallexperiments,NRS units were lled with a nutrient solutionwithtotal Nconcentrationat 11.29mgL1(NO3-N:NH4-N = 3:1) and P concentration at3.1 mgL1while othernutrients in the solu-tion were kept consistent (Table 2). These Nand P concentrations were within the rangesof inorganic N and P concentrations reportedin stormwater retention structures (Moustafa,1999; Serrano and DeLorenzo, 2008). Watersource was municipal water ltered through atwo-holder B-Pure water purication systemhousedwithacarbonlterandadeionizerlter (D0813 and D0749; Barnstead Interna-tional, Dubuque, IA).Datacollection. Duringanexperiment,thesolutionlevels intherell tanks wererecorded daily at 1PM. Daily water consump-tion of a unit was calculated as the differencebetween readings of 2 consecutive days.Total solution consumption of a unit wasthe sum of daily water consumption of a unitthroughout an experiment. Total Nand Pprovidedtoaunitwerecalculatedas:(totalsolution consumption per unit + 284 L initialll solution) treatment NorPconcentra-tions. Water consumed by a unit is a result ofplant evapotranspiration and water loss fromthesurfacesofunitcomponents.Waterlossbyunit surface evaporationwas estimatedwiththeNRSoperatingwiththepots andmediainthegrowthcontainersbut withoutthe plants for 7 consecutive days. An averageof 0.03 0.02 Ldaily loss per unit wasrecorded, which was negligible comparedwith the amount of plant consumption. Aver-agedailywater consumptionper plant wasthen calculatedby dividing daily watercon-sumption of a unit by 6 (plants).Watersamplesof100mLsolutionwerecollected from the reservoir tanks between 1PM and 4 PM into acid-washed Nalgene bottlesevery 7d. Eachsample was lteredthrough0.2-mmpolytetrauoroethylene membraneltersintotwo50-mLwatersamplebottles.Onebottleofthesamplewasacidiedwith2mLof sulfuricacid(2N) tochemicallystabilize the sample and stored at 4 C.Anotherbottleofthesamplewasnotacidi-ed and sent for nitrate and nitrite analyses atthe EPA-approvedwateranalysislaboratoryat theLouisianaStateUniversityAgCenterDepartment of Agricultural Chemistry. Attheendofanexperiment,allacidiedsam-pleswereanalyzedtodeterminetotalPandammoniaconcentrations.TotalPwasdeter-minedbycolorimetricanalysis(EPA365.3;EPA, 1983). Ammoniawas determinedbythe SM4500-NH3_E method. Nitrate andnitrite concentrations were determined by ionchromatography (EPA 300.0; EPA, 1983).Plantswereharvestedafterbeinggrownin the NRS for 10 weeks. Plants wereremovedfromthenetpotsandweighedforfreshweight. Shoots(includinginorescen-ces), rhizomes, and roots were washed inmunicipal water for 30 s. Rhizomes of arrowarum, iris, and calla lily were sliced into thinpieces. All samples were dried at 70 C untilweight became constant to determine dryweight. Dried tissue sample was ground in aWiley Mill (Swedesboro, NJ) to pass through40-mesh (0.425 mm) screen. Tissue analyseswereconductedbyLouisianaStateUniver-sity Soil Testing and Plant Analysis Labora-tory. Tissue N concentration was determinedbyanLECOTruSpecCNnitrogenanalyzer(LECO, St. Joseph, MI).Statistical analyses. The experimentaldesign was randomized complete blockdesignwiththree treatments (species) andtwoblocks(NRSunits)forallexperiments.The NRS units were arranged parallel to thegreenhouse cooling pads so that blockingaccounted for the temperature gradient inthe greenhouse. The six plants, each in agrowth container withina unit, were sub-samples. Expt. 1 was repeated and data werepooled because no signicant difference wasfound between the two experiments. Analysesofvariancewasperformedtotest treatment(species) signicance in each experiment witha=0.05. Fishersprotectedleastsignicantdifference was used to separate means. Anal-yses were conducted using SAS Version 9.1.3(SAS Institute, Cary, NC).Results and DiscussionPlant water consumption. Daily waterconsumptionuctuated throughoutthe threeexperiments (Fig. 1). Canna had the greatestdaily water consumption in Expt. 1 (1.4 L perplantperday;Fig.1A).AtWeek10,cannaconsumed an average of fourfold more waterthan arrowarumand vefold more water thaniris. In Expt. 2, pickerelweed (1.1 L per plantTable 2. Chemical formulations and elemental concentrations of the treatment solution in threeexperiments conducted in a nutrient recirculation system (NRS).Nutrient solution formulationsChemical Molecular mass (gM1)Stock solutionconcn (mM) To use (mLL1)MacronutrientsNH4NO380.04 1,000 0.2Ca(NO3)24H2O 236.15 1,000 0.2KH2PO4136.08 1,000 0.1K2SO4174.25 500 0.25CaCl22H2O 147.02 1,000 0.6MgSO47H2O 246.5 1,000 0.5Micronutrients (mixed in 1-gallon container)EDTA-Fe 367.10 100 0.04H3BO361.83 100 0.27zMnCl24H2O 197.91 10(NH4)6Mo7O244H2O 1,235.86 1ZnSO47H2O 287.54 1CuSO45H2O 249.68 1Elemental concentrations (mgL1)Element ConcnNH4-N 2.89NO3-N 8.40Total N 11.29Phosphorus 3.10Potassium 23.46Sulfur 24.10Calcium 32.06Magnesium 12.15Iron 2.23Manganese 0.55Copper 0.05Boron 0.54Zinc 0.05Molybdenum 0.67Chloride 36.16zMicronutrients B, Mn, Mo, Zn, and Cu were prepared in one solution and used at 0.27 mLL1.1706 HORTSCIENCE VOL. 44(6) OCTOBER 2009per day; Fig. 1B) consumed more water thandwarf papyrus (0.67 L per plant per day) andbulltonguearrowhead(0.71Lperplant perday). In Expt. 3, water consumption by cannawasthegreatest,followedbypickerelweed,and with calla lily having the least waterconsumption(Fig.1C).Ourresultsaresim-ilar to those reported from a laboratory-scalewetland study (Polomski et al., 2007), inwhichcannaandpickerelweedhadgreaterwater consumption than other species. How-ever, GoldenFleece irisinour studycon-sumed much less water than hybrid Louisianairis Full Eclipse in their study, indicating apossible difference between iris cultivars.Biomass accumulation. At harvest,Australia canna accumulatedthe greatesttotal biomass as indicated by plant dry weightcompared with arrow arum and iris (Table 3).When using shoot dry weight as an indicationof harvestablebiomass, cannaaccumulated10-and15-foldmoreharvestablebiomassthanarrowarumand iris, respectively. InExpt. 2, pickerelweed and dwarf papyrus hadsimilar total biomass, but the former hadgreater harvestable biomass. In Expt. 3, cannahad more total and harvestable biomass thanpickerelweed. Becausecallalilybulbs hadconsiderably higher initial biomass than sin-gle plants of canna and pickerelweed, we didnot compare the biomass production of callaFig. 1. Daily water consumption of four ornamental plants compared with three wetland species commonly used in stormwater treatment in three experimentsconducted in a nutrient recirculation system (NRS) from 2005 to 2007. The six units of the NRS were planted with three plant species in each experiment. (A)Australia canna, Golden Fleece iris, and arrow arum in Expt. 1. (B) Dwarf papyrus, pickerelweed, and bulltongue arrowhead in Expt. 2. (C) Australiacanna, calla lily, and pickerelweed in Expt. 3.Table3.Dryweightoftheshoots,rhizomes, androotsofornamentalandwetlandplantsgrown for10weeks in a greenhouse nutrient recirculation system with total nitrogen and phosphorousconcentrations of 11.29 and 3.1 mgL1in three experiments conducted from 2005 to 2007.SpeciesDry wt (g)Shoot RhizomezRoot TotalExpt. 1yCanna 89 ax(83%)w9.22 (8%) 9.36 a (9%) 107.58 aArrow arum 8.96 b (49%) 6.03 (33%) 3.41 b (18%) 18.4 bIris 5.83 b (44%) 4 (30%) 3.4 b (26%) 13.23 bLSD0.0511.7 NSv2.20 17.93Expt. 2Pickerelweed 56.12 a (84%) 2.4 (3%) 8.53 (13%) 67.05Dwarf papyrus 43.07 b (86%) 7.18 (14%) 50.25Bulltongue arrowhead 42.85 b (84%) 8.33 (16%) 51.18LSD0.0513 NS NSExpt. 3uCanna 78.8 a (78%) 11.8 (11%) 10.5 (11%) 101.1 aPickerelweed 51.9 b (84%) 3 (5%) 6.5 (11%) 61.4 bLSD0.0514.5 NS NS 21.8zBecause dwarf papyrus and bulltongue arrowhead did not form harvestable rhizomes during the 10-weekgrowth period, data for rhizome were not available.yExpt. 1 was repeated and data were pooled because no signicant difference was found between the twoexperiments. Initial biomass of the plant species evaluated in Expts. 1 and 2 were similar as indicated byplant fresh weight measured at transplant (data not presented).xMeanswithinavariablecolumnof anexperiment not followedbythesameletter aresignicantlydifferent by Fishers protected least signicant difference (LSD). a = 0.05. N = 24 in Expt. 1 and N = 12 inExpts. 2 and 3.wPercentage in parenthesis are the percentage of root, shoot, or rhizomes in total plant dry weight.vTreatment (species) effect was nonsignicant (NS) (P > 0.05).uCalla lily was not included in the comparison of plant dry weight in Expt. 3 because the initial biomass ofcalla lily bulbs was signicantly higher than the biomass of canna and pickerelweed as indicated by plantfresh weight measured at transplant (data not presented).HORTSCIENCE VOL. 44(6) OCTOBER 2009 1707lily with the other speciesin Expt. 3.Cannaand pickerelweed were also reported ashaving high biomass production in otherstudies (Belmont and Metcalfe, 2003; Polom-ski et al., 2007).Within the 10-week period of growth, allplantsexceptdwarfpapyrusandbulltonguearrowhead had rhizomatous underground tis-sue. There was a signicant difference amongspecies in terms of above-/underground bio-mass allocation. For example, in Expt. 1,80%of the total biomass in canna wasaboveground and thus harvestable. On contrast,only 48.7% of the total biomass in arrow arumand44.1%iniris wereharvestablebecauseunderground rhizomes alone accounted for32.8% and 30.2% of the total biomass in thesespecies, respectively (Table 3).Plant tissue nutrient concentration. Planttissue nutrient concentrations are oftenreportedinwatermitigationstudiestocom-pare plant nutrient removal ability. Inourstudy, canna, iris, pickerelweed, and bull-tonguearrowheadhadhigher Nconcentra-tions inshoots thaninrhizomes androots(Table4). Nitrogentissueconcentrationsincanna, iris, andpickerelweedinour studywere higher than those reported by Polomskiet al. (2007)inwhichdifferent cultivarsofthese species were grown in 10.44 mgL1Nand 1.86 mgL1P, suggesting that plants mayuse more N at higher P loading rates.Tissue P concentration was generallyhigher inshootsthanrootswithcannaandarrowarum(Expt. 1), pickerelweed, andbulltongue arrowhead (Expt. 2) havinghigher tissue P concentrations than otherspecies.Phosphorus concentrationsin cannain our study were also higher than thosereported by other studies with similar P treat-ment levels but different cultivars (DeBusket al., 1995; Hadad and Maine, 2007; Polomskiet al., 2007). Phosphorous concentrationinbulltonguearrowheadwasalsohigherthananaturalpopulation(RichardsandIvey,2004)suggestingluxuryconsumptionof Pinourstudy.Planttissuenutrientcontent.Becauseofgreater shoot biomass accumulation, cannaandpickerelweedhadhighershootNandPcontent than other species in Expts. 1 and 2,respectively (Table 5). As a result, whencomparingnutrient allocationamongshoot,rhizome,androot,ahigherpercentageofNandPcontentwasfoundinshootsofcanna(86%total N and 89%of total P) andpickerelweed(85%total Nand89%totalP). On contrast, arrowarumand iris hadsignicantlyhigher percentages of total NandPcontent inrhizomes, andonly48.7%and59.1%total Ncontent and64.2%and68.1% total P content were in shoots. Specieswithhighershoot NandPcontent suchascannaandpickerelweedaredesiredbecauseshoot biomass can be harvested by the end ofa growing season(s) to remove nutrient fromthe treatment system.Nutrient concentrations in the nutrientrecirculationsystemunits. ByanalyzingN(ammoniumand nitrate) and P (total P)concentrationsinsolutionsamplescollectedevery week, we quantied plant nutrientremovalabilityfromtheperspectiveofsys-temnutrient reduction. Nitrateandammo-nium were provided in treatment solution at a3:1 ratio preferred by most plant species(Marschner, 1995). At Week 10, ammonium(NH4+) Nwasundetectable(lessthan0.03mgL1) in all unit solutions. This wasexpected because other than plant uptake,nitrication of NH4+to NO3could decreaseitsconcentration. Inallexperiments, nitrateconcentrationoftreatment solutionremain-ing in NRS units uctuated and generally de-clined over the second half of the experiments.Table4. Tissuenitrogen(N) andphosphorous (P) concentrations inshoots, rhizomes, androots ofornamental and wetland plants grown for 10 weeks in a greenhouse nutrient recirculation system withtotalNandPconcentrationsof11.29and3.1mgL1inthreeexperimentsconductedfrom2005to2007.SpeciesN concn (% dry wt) P concn (% dry wt)Shoot RhizomezRoot Shoot Rhizome RootExpt. 1yCanna 1.51 bx0.91 c 1.25 0.44 ab 0.11 0.18Arrow arum 1.32 b 1.31 b 1.33 0.53 a 0.27 0.30Iris 2.72 a 1.7 a 1.23 0.39 b 0.13 0.16LSD0.050.33 0.21 NSw0.09 NS NSExpt. 2Pickerelweed 1.78 b 1.05 1.65 ab 0.51 a 0.22 0.24Dwarf papyrus 1.61 b 1.82 a 0.37 b 0.21Bulltongue arrowhead 2.1 a 1.4 b 0.50 a 0.19LSD0.050.27 0.22 0.13 NSExpt. 3vCanna 1.86 1.12 1.29 0.41 0.17 0.34Pickerelweed 1.95 1.31 1.54 0.48 0.18 0.22LSD0.05NS NS NS NS NS NSzBecause dwarf papyrus and bulltongue arrowhead did not form harvestable rhizomes during the 10-weekgrowth period, data for rhizome were not available.yExpt. 1 was repeated and data were pooled because no signicant difference was found between the twoexperiments.xMeanswithinavariablecolumnof anexperiment not followedbythesameletter aresignicantlydifferent by Fishers protected least signicant difference (LSD). a = 0.05. N = 24 in Expt. 1 and N = 12 inExpts. 2 and 3.wTreatment (species) effect was nonsignicant (NS) (P > 0.05).vBecausethebiomass(andpossiblynutrientcontents)incallalilybulbswassignicantlyhigherthancannaandpickerelweedasindicatedbyplantfreshweightattheinitiationoftheexperiment(datanotpresented). It is possible that tissue N and P concentrations may be affected by the nutrient reallocationfrom bulbs to shoots and roots. Therefore, N and P concentrations in calla lily were not compared in Expt. 3.Table 5. Tissue nitrogen (N) and phosphorous (P) contents of the shoots, rhizomes, and roots of ornamentalandwetlandplants grownfor 10weeks inagreenhousenutrient recirculationsystemwithtotalnitrogen and phosphorous concentrations of 11.29 and 3.1 mgL1in three experiments conducted from2005 to 2007.SpeciesN content (mg/plant) P content (mg/plant)Shoot RhizomezRoot Shoot Rhizome RootExpt. 1yCanna 1,343.9 ax83.9 117 a 391.6 a 10.1 a 16.8 aArrow arum 118.3 b 52.8 72 b 47.5 b 10.9 a 16.2 aIris 158.6 b 68 41.8 b 22.7 c 5.2 b 5.4 bLSD0.05135.1 NSw43.55 22 4.5 2.6Expt. 2Pickerelweed 998.9 a 25.2 140.8 286.2 a 5.3 20.5Dwarf papyrus 693.4 c 130.7 168.2 b 15.1Bulltongue arrowhead 899.9 b 116.6 214.3 b 15.8LSD0.0598.6 NS 69.6 NSExpt. 3vCanna 1,465.7 a 132.2 a 135.5 323.1 a 20.1 a 35.7 aPickerelweed 1,012.1 b 39.3 b 100.1 249.1 b 5.4 b 14.3 bLSD0.0579.5 66.3 NS 60.07 12.9 17.6zBecause dwarf papyrus and bulltongue arrowhead did not form harvestable rhizomes during the 10-weekgrowth period, data for rhizome were not available.yExpt. 1 was repeated and data were pooled because no signicant difference was found between the twoexperiments.xMeanswithinavariablecolumnof anexperiment not followedbythesameletter aresignicantlydifferent by Fishers protected least signicant difference (LSD). a = 0.05. N = 24 in Expt. 1 and N = 12 inExpts. 2 and 3.wTreatment (species) effect was nonsignicant (NS) (P > 0.05).vCalla lily was not included in the comparison of tissue N and P contents in Expt. 3 because the biomass(and possibly nutrient contents) of calla lily bulbs was signicantly higher than canna and pickerelweed asindicated by plant fresh weight at the initiation of the experiment (data not presented).1708 HORTSCIENCE VOL. 44(6) OCTOBER 2009FromWeeks5to10, nitrateconcentrationsin units planted with canna (Fig. 2A, Expt. 1)waslowerthanthoseinotherunitsateverysample dates. Nitrate concentrations in unitsplantedwithpickerelweed, dwarf papyrus,and bulltongue arrowhead declined overtime. However, nitrate concentrations inunits planted with iris, arrow arum (Fig. 2A,Expt. 1), andcalla lily(Fig. 2A, Expt. 3)remainedhighattheendofExpts.1and3,respectively.Total Pconcentrations of nutrient solu-tionsremaininginunitsplantedwithcanna(Fig. 2B, Expt. 1), pickerelweed, dwarf papy-rus, and bulltongue arrowhead (Fig. 2B, Expt.2) declined with time during the experiments.Units planted with iris, arrow arum, and callalilyhadsignicantlyhighersolutionPthanother units at Week10inExpts. 1and3.BecausePconcentrationusedinour studywas close to the highest concentrations foundin stormwaterretentionstructure, itis likelythat thisconcentrationexceededtheuptakeabilityofsome plantspeciesandresultedinluxury consumption of P. This was alsosuggestedby Zhangetal.(2008),thatwhenPavailabilityinwaterexceedsplantuptakeand assimilation capacity, soil and ltermedia of the treatment structure becomemore effective than plants in P removal fromthe water column.Total nitrogenandphosphorus removalfromthenutrientrecirculationsystemunits.Over the 10-week period, we did not observefoliageor root senescencethat mayreturnplant tissue into the unit and decompose.Total N and P removedby a NRS unit werecalculated based on N and P remaining in theunit and the N and P received throughout theexperiments. In addition to plant uptake,pottingmediaadsorptionandmicro-organ-ism and algae denitrication can also removeN and P from the NRS. Because plant uptakehas beenreportedtobethemajor nutrientremovalmechanismsinplantedconstructedwetlands (Zhanget al., 2007), we didnotquantify other possible removal pathways inthis study. Instead, nal system recovery ratewas calculated as percentage of nutrientremoved by plants and all possible othermechanismsout of total nutrientsreceived.The units plantedwithcannareceivedthegreatest nutrients than units planted withotherspeciesinExpt. 1, andcannahadthehighest perunit NandPrecoveryrateandtotal amount of N and P recovered (Table 6).Units planted with pickerelweedhad similarN and P recovery rate as canna in Expt. 3 buta less amount of Nand Pwas recoveredbecause a less amount of solution was pro-cessed. Units planted with arrow arum andiris in Expt. 1 and calla lily in Expt. 3 had thelowest NandPrecoveryrateandtheleastamountofNandPremoved.HighNandPrecovery rates of canna found in our study aresimilar to that of other hybrid canna andCanna indica reported by laboratory-scalestudies (Zhang et al., 2007; Zurita et al.,2006), but higher than a eld pilot-scalestudies (Ayaz and Akca, 2001; Tuncsiperet al., 2005). The optimum growing conditioninthegreenhousecouldhavecontributedtothe superior plant growth and nutrient removalingreenhousestudies. Performanceof callalily was similar to that found in a laboratory-scale constructed wetland study where higherNandPtreatmentconcentrationswereused(Belmont and Metcalfe, 2003).Theobjectiveofthisstudywastoassessthefeasibilityofusingornamentalplantspe-cies to remove nutrient pollutions from storm-water treatment structures. Compared withobligatewetlandspecies arrowarum(Expt.1) and pickerelweed (Expt. 3), Australiacanna had great potential to be used asnutrient bioltration plants in stormwatermitigation attributed to its high biomassFig.2.Nitrate-N(A)andtotalphosphorus(P)(B)concentrationsinweeklysolution samplestakenfromanutrientrecirculationsystem(NRS)planted withornamental or wetland species in three experiments. Plant species evaluated in Expt. 1 were Australia canna, arrow arum, and GoldenFleece iris. Speciesevaluated in Expt. 2 were pickerelweed, dwarf papyrus, and bulltongue arrowhead. Species evaluated in Expt. 3 were Australia canna, pickerelweed, andcalla lily. Nitrate and total P concentrations were 8.4 mgL1and 3.1 mgL1, respectively, in the original treatment and rell solutions.HORTSCIENCE VOL. 44(6) OCTOBER 2009 1709production and high harvestable tissue N andPcontent. DwarfpapyrushadsimilarshoottissueNconcentrationaspickerelweedbutlower shoot biomass and thus lower harvest-able nutrient content. Golden Fleece irishad higher tissue N concentrations thancannabut muchlower biomassproduction,and this was further compromised by the factthat the majority of the assimilated nutrientswere stored in underground rhizome and thusnot readily harvestable. From the perspectiveof NRS treatment system performance, unitsplantedwithcannahadthehighestNandPremoval among all species, whereas otherornamental species showed less effectivenessin removing N and P from the system.Resultsfromthisstudysuggest that theornamental species canna has the potential tobeusedasmitigationplantsinurbanstorm-water oating bioltration treatment. Becausecannaisaperennial plant andallocatesthemajority of its biomass to shoots, it is possibleto regularly harvest and remove biomass fromthe treatment system. However, more researchneeds to be done to evaluate factors that mightaffect its application such as N and P loadingandhydraulicconditions, plantingdensities,poly culture, harvesting frequency, and growthmaintenance techniques.Literature CitedAsaeda, T., L. Rajapaks, and T. Fujino. 2008.Applications of organ-specic growth models;modelling of resource translocation and therole of emergent aquatic plants in elementcycles. Ecol. Modell. 215:170179.Ayaz, S.C. and L. 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Total nutrient solution consumption, nitrogen (N) and phosphorous (P) received, recovered, and the Nand P recovery by the nutrient recirculation system(NRS) units planted with ornamental and wetland plants in three experiments conducted from 2005 to 2007.zSpeciesSolutionconsumptiony(L/unit)Nutrient receivedx(mg/unit) Nutrient recoveredw(mg/unit) Nutrient recovery ratev(%)N P N P N PExpt. 1uCanna 590.9 at9,877.6 a 2,712.2 a 9,749.2 a 2,489.8 a 98.7 a 91.8 aArrow arum 129.9 b 4,672.9 b 1,283.1 b 1,476.6 b 494.0 b 31.6 b 38.5 bIris 103.7 b 4,377.1 b 1,201.9 b 1,378.8 b 316.1 b 31.5 b 26.3 bLSD0.0552.3 590.5 162.1 825.8 303.2 33.6 36.9Expt. 2Pickerelweed 460 a 8,399.8 a 2,306.4 a 7,400.2 a 1,877.4 a 88.1 81.4Dwarf papyrus 281.3 b 6,382.2 b 1,752.4 b 5,450.4 b 1,247.7 c 85.4 71.2Bulltongue arrowhead 296 b 6,548.2 b 1,798 b 5,939.2 b 1,465.4 b 90.7 81.5LSD0.0537.5 423.4 116.3 1,070.4 188.6 NSsNSExpt. 3Canna 596.4 a 9,939.7 a 2,729.2 a 9,711.1 a 2,516.3 a 97.7 a 92.2 aPickerelweed 422.3 b 7,974.1 b 2,189.5 b 7,049.1 b 1,817.3 b 88.4 a 83 aCalla lily 113.04 c 4,482.6 c 1,230.8 c 1,560 c 327.4 c 34.8 b 26.6 bLSD0.0549.2 555.5 152.5 616.4 119.8 20.6 16.5zAll NRS units were lled with a treatment solution of 11.29 mgL1total N and 3.1 mgL1total P at the initiation and during the experiments.yTotal solution consumption per unit was the sum of daily solution consumption by a unit over an experiment. 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