ACTAECOLOGICASINICAVolume28,Issue2,February2008OnlineEnglisheditionoftheChineselanguagejournalCitethisarticleas:ActaEcologicaSinica,2008,28(2),525−533.Receiveddate:2006-12-24;Accepteddate:2007-08-23*Correspondingauthor.E-mail:yugr@igsnrr.ac.cnCopyright©2008,EcologicalSocietyofChina.PublishedbyElsevierBV.Allrightsreserved.RESEARCHPAPERResponsesofwateruseefficiencyof9plantspeciestolightandCO2andtheirmodelingWangJianlin1,YuGuirui2,*,FangQuanxiao1,JiangDefeng1,QiHua3,WangQiufeng21QingdaoAgriculturalUniversity,Qingdao266109,China2InstituteofGeographicSciencesandNaturalResourcesResearch,ChineseAcademyofSciences,Beijing100101,China3ShenyangAgriculturalUniversity,Shenyang110161,ChinaAbstract:Photosynthesiscoupledwithtranspirationdetermineswateruseefficiency(WUE)atleaflevel,andtheresponsesofWUEcontrolledbygasexchangesthroughstomatatoenvironmentarethebasisofcarbonandwatercyclesintheecosystem.Inthispaper,byusingLi-6400PortablePhotosynthesisSystem(LI-COR),WUEatleaflevelwasanalyzedundercontrolledphotosyntheticphotonsfluxdensity(PPFD)andCO2concentrationconditionsacross9plantspeciesincludingmaize(Zeamays),sorghum(Sor-ghumvulgare),millet(Setariaitalica),soybean(Glycinemax),peanut(Arachisphyogaea),sweetpotato(Ipomoeabatatas),rice(Oryzasativa),Massonpine(Pinusmassoniana)andSchimasuperba.Wehaddevelopedanewmodeltoestimatethewateruseeffi-ciencyinresponsetothecombinedeffectsoflightandCO2concentration.Ourmeasureddatavalidatedthatthismodelcouldsimu-latethechangesofwateruseefficiencyverywellundercombinedeffectoflightandCO2concentration.ItcouldbeusedtoestimatecontributionofphotosynthesisincreaseandtranspirationdeclineonwateruseefficiencywiththerisingofCO2concentration.GreatdifferencesinwateruseefficiencyoccurredinthesedifferentplantspeciesundervariousCO2concentrationlevels.Basedonwateruseefficiencyatregionalscale,weconcludedthatplantsshouldbeseparatedintoC3plantsandC4plants,andfurthermore,C3plantsshouldbeseparatedintoherbaceousplantsandwoodyplants.Ourseparationcriteriawoulddoagreatfavorinmodelingtheevapo-transpirationofterrestrialecosystemwithcarbonandwaterbalance.KeyWords:wateruseefficiency(WUE);photosyntheticphotonsfluxdensity(PPFD);CO2concentration;modelingWateruseefficiency(WUE)isexpressedasassimilationproductionperunitwater.Asanimportantindexforplantenergyconversion,WUEhasbeenappliedwidelyinmanyfields[1].TheconceptsanddefinitionsofWUEamongdiffer-entfieldsandscalesaredifferent[2].Atleaflevel,WUEistheratioofnetphotosynthesisrate(Pn)andtranspirationrate(Tr),whicharecoupledwithoneanotherunderstomatalregula-tions.Pnistheprimarydriveforplantproduction,evolutionandglobalcarboncycle,whiletranspirationdriveswatercycleinsoilplantatmospherecontinuum(SPAC)andecosystem.Therefore,modelingplantWUEisthekeyindextoevaluatetheinteractionsbetweenwaterandcarboncyclesintheeco-system.PlantPn,Tr,stomatalconductanceandWUEarein-fluencedbysolarradiationandCO2densityandotherenvi-ronmentalfactors;ontheotherhand,theyshowpowerfulselfregulationsandadaptationstotheseenvironmentalfactors[3,4].Stomataregulatetherelationbetweencarbonassimilationandwatertranspiration,butthetransferdirectionsbetweencarbonandwateraredifferent.Carbonassimilationcanreachmaxi-mumbystomatalregulations;ontheotherhand,thestomatalregulationsareconstrainedbyphotosynthate[5–9],whichresultsindifferentsynchronizationsbetweenCO2andwaterexchangesandvariou...
