Lecture3&4:TerrestrialCarbonProcessI.Photosynthesisandrespiration(revisit)II.CarbonStocksandFluxesinTerrestrialEcosystemsIII.TerrestrialEcosystems

A.EcosystemConcept

B.EcosystemCarbonBalance(GPP,NPP,NEP,NBP)

VI.Missingcarbonsinks?Lecture3:PhotosynthesisandRespiration1.WhatisthePhotosynthesis?2.

WherethePhotosynthesisOccurs?3.HowPhotosynthesisworks?–KeyProcesses

4.AlternativePhotosynthesisPathwayPhotosynthesisOverview1.WhatisthePhotosynthesis?Photosynthesis

isthebiogeochemicalprocessbywhichPlantscoveratmosphericCO2tocarbonproductionsthatresultsinplantgrowth

istheconversionoflight-energytochemical-energyviathechloroplasts

generates170billionmetrictonsofsugarannually,whichentersourbiosphereWeexpressthiscombinedknowledgeasthephotosyntheticequation:6CO2+12H2O+lightenergy--->C6H12O6+6O2+6H2O(orCO2+2H2O+lightenergy--->CH2O+O2+H2O)Photosynthesistakesplacewithinleaf(orgreenstem)cellscontainingchloroplastse.g.eachcellcontains40to50chloroplastsachloroplasthasdozensofthethylakoidsand

millionsofpigmentmolecules

eachthylakoidcontainsthousandsofphotosystems2.

WherethePhotosynthesisOccurs?PhotosyntheticOverviewA.Therearethreebasicstepsinphotosynthesis:

(1)LightReactions

-energycapture

(2)DarkReactions

-fixationofcarbon

(3)

PigmentRegenerationelectronreplacementfromthesplittingofH2Oinoxygenicphotosynthesis.3.HowPhotosynthesisworks?–keyprocesses

C3photosynthesis(three-carbonsugars)–C3plant(2)CrassulaceanAcidMetabolism(CAM)

(1)C4Photosynthesis

4.AlternativePhotosyntheticPathwaysSomeplants(e.g.,corn,sugarcane,andmanytropicalgrass)beginthephotosyntheticprocessbyproducingafour-carboncompounds.PlantsofthistypearecalledC4plants(e.g.liveinhotanddryenvironmentsandareabletophotosynthesizeatlowCO2concentration)LikeC4plant,CAMisanadaptationtohotdryenvironmentsCAMplatsutilizeboththeC3andtheC4pathwaysofphotosynthesisCO2isfixedbyPEP(phosphhoenolpyruvate)carboxylaseatnighttoformmalicacidwhichisthenisstoredinthevacuoleofthecell. RespirationOverview1.AutotrophicRespiration(PlantRespiration)

A.MaintenanceRespiration

B.GrowthRespiration

2.HeterotrophicRespiration(SoilRespiration)1.AutotrophicRespiration(Ra)RainvolvestheoxidationoforganicsubstancestoCO2andwater: CH2O+O2--->CO2+2H2O+energyTotalautotrophicrespiration(Ra)consistsoftwomajorcomponents:(1)MaintenanceRespiration(Rm)(2)GrowthRespiration(Rs)MaintenanceRespiration:thebasalrateofmetabolism,includestheenergyexpended

onionuptakeandtransferwithinplants.

(a)Thetemperatureismostimportantenvironmentalfactoraffectingmaintenancerespiration

Proteinsynthesisratesincreaseexponentiallywithincreasingtemperature(T)(b)TheTdependenceofRmisexpressedintermoftheQ10,orchangeinratewitha10oCriseintemperature:

Rm(T)=R0Q10

[(T-T0)/10]Where:R0

isthebasalrespirationrateatT=0oC(orref.T)

Q10representsthechangeintherateofrespirationfor10oCchange inT(about2.0-2.3)(c)usingplantnitrogencontentMichealRyan(1991)derivedanempiricalrelationshipbasedonawidevarietyofspeciesandplanttissues:

Rm=0.0106NWhereRmismaintenancerespiration(molesCperhour),andNisplantnitrogeninmolesofN.(seeRyan1991,EcologicalApplications,1:157-167).MostoftheorganicNinplantsisinproteinandabout60%Rmsupportsproteinrepairandreplacement(2)GrowthRespiration(Constructionrespiration)(a)Rgincludesthecarboncostofsynthesizingnewtissuefromglucoseandminerals.(b)Rgforvarioustissuesdiffer,dependingonthebiochemicalpathwaysinvolved.e.g.:1gligninrequires2.5gofglucose

1gneedlesrequire1.28gofglucose1grootsrequire1.2gofglucose

(C)Growthrespirationcanbeestimatedbasedonconstructioncost

EstimatingGrowthrespiration(Rg)GrowthrespirationisgenerallyconsideredtobeindependentoftemperatureandisproportionaltoGPP:Whererg,iisagrowthrespirationcoefficientforplantcomponenti,andra,iisthecarbonallocationfractionforplantcomponenti.Ryan(1991)used25%foroverallandrootgrowthrespirationcoefficient.IntheTEM(Melliloetal.1993),20%ofGPPisappliedtogrowthrespiration.

2.HeterotrophicRespiration(Rh)1)ConceptTheformofrespirationbywhichorganicmatterisconvertedbackintoCO2,mainlybysoilmicro-organisms.2)ModelingRhSoilrespiration(totalsoilCO2flux)including:

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