SoilRespirationStephenBonnageDirectorSoilRespirationandtheCarboncycleSoil:4thlargestpool2ndlargestsourcetoatmosphereSoilRespirationQ.Whatissoil?Soilisacomplexmixtureofmineralmatter,organicmatterandlivingorganismsSoilRespirationWhataretheorganisms?

RootsAlgaeBacteriaFungiEarthwormsInsectsSoilRespirationQ.Howmany?A.1gramofsoiltypicallyholdsmoreorganismsthantherearepeopleontheEarth109microbesin1gramofsoilSoilRespirationQ.Whatissoilrespiration?A.Alllivingorganisms,whetheranimalormicrobe,produceCO2gasasaby-productoftheprocessofrespiration.SoilRespirationAsRaichandSchlesinger(2002)pointout,

"TherateatwhichCO2movesfromthesoiltotheatmosphereiscontrolledbytherateofCO2productioninthesoil(thetruesoilrespirationrate),thestrengthoftheCO2concentrationgradientbetweenthesoilandtheatmosphere,andpropertiessuchassoilporesize,airtemperatureandwindspeedthatinfluencethemovementofCO2throughandoutofthesoil."Thesefactorswillbeimportanttoconsiderwhenassessingvariousattemptstoquantifymeasurementmethodologies.

SoilRespirationRaichandSchlesinger(1992)estimatedthatglobalsoilrespirationconsistsof50PgC/yearfromdetritusand18PgC/yearfromliverootsandmycorrhizae.Soilrespirationrateshavebeenreportedtobehigheringrasslandsthaninforests,andhigherindeciduousforeststhaninconiferousforests

SoilRespirationRaichandTufekcioglu(2000)reportedinareviewpaperthatrootcontributiontototalsoilrespirationishighincold,northernclimatessuchasarctictundra(50-93%)andborealforests(62-89%).Temperateforestsarelower,with33-50%inbroad-leavedforests,35-62%inpineforests,and12-40%ingrasslandsandcroplands.Duetothewiderangeofthereportedvalues,theycouldnotestablishacorrelationbetweenvegetationtypeandrootcontributiontosoilrespiration.Soilpropertiessuchastemperature,moisture,andsubstratepropertieswerefoundtobethemostinfluentialfactorsdeterminingsoilrespiration.

SoilRespirationSoilrespirationhasbeenshowntobestronglyinfluencedbytemperature(LloydandTaylor1994,FangandMoncrieff2001).Respirationsincreasesexponentiallywithtemperature.ThetemperaturedependenceofsoilisoftendescribedbytheQ10value.Generallydefined,thisfactorrepresentsthedifferenceinrespirationratesovera10degCinterval;however,thereissomedebateastohowQ10iscalculatedbasedonwhattemperaturerangetouseandwhichequationbestdescribesrespiration'stemperaturedependence.FangandMoncrieff(2001)suggesttheequation:

Q10=(R2/R1)^10/(T2-T1)

forfirst-orderexponentialfunctions,whereR1andR2aremeasuredrespirationratesattemperaturesT1andT2,respectively.

SoilRespirationLloydandTaylor(1994)foundthattherelativesensitivitytotemperaturechangeismuchgreaterforsoilsatlowtemperaturesthanforwarmersoils.Forexample,intheabsenceofmoisturelimitations,anincreasefrom0to1degCwouldresultina22%increaseinrespiration,whileanincreasefrom25to26degCleadstoa5%increase.Thus,modestglobalchangescenariosresultingina1to2degCincreaseinmeantemperaturewouldhavethemostsignificanteffectonthe60gC/m2yearrespiredbytundra.

SoilRespirationKirschbaum(1995)comparedpublishedrespirationdataandfoundthatQ10valuesdecreasedwithincreasingtemperature.HeconcludesthattemperaturerisewillleadtoincreasedcontributionofatmosphericCO2fromsoil.ThistrendmayfeedbackuponitselfaselevatedCO2promotesprimaryproduction,increasinginputstosoilorganicmatter,andfurtherincreasingrespiration.Nevertheless,thecontributionofsoiltototalatmosphericCO2isnotexpectedtobeasimportantasfossilfuelcombustionordeforestation.

SoilRespirationQ.Howcanwemeasureit?A.Chambertechniques,eddycovariance,

SoilRespirationClosedSystemSoilRespirationOpenSystemSoilRespirationAttemperaturesover35degreesCelsius,rootrespirationbeginstoshutdowncompletelyWhy?A.EnzymaticactivityisinterruptedSoilRespirationMicroorganismsaredividedintothreetemperaturegroups;cryophiles,mesophilesandthermophiles.Cryophilesfunctionoptimallyattemperaturesbelow20degreesCelsius,mesophilesfunctionbestattemperaturesbetween20and40degreesCelsiusandthermophilesfunctionoptimallyatover40degreesCelcius.Innaturalsoilsmanydifferentcohorts,orgroupsofmicroorganismsexist.ThesecohortswillallfunctionbestatdifferentconditionssorespirationmayoccuroveraverybroadrangeSoilRespirationSoilmoistureisanotherimportantfactorinfluencingsoilrespiration.Soilrespirationislowindryconditionsandincreasestoamaximumatintermediatemoisturelevelsuntilitbeginstodecreasewhenmoisturecontentexcludesoxygen.SoilRespirationHowever,studieshaveshownthatsoilmoistureonlylimitsrespirationatthelowestandhighestconditionswithalargeplateauexistingatintermediatesoilmoisturelevelsformostecosystems.Hmmmmm!SoilRespirationSoilRespirationTemporalVariabilityHowfluxrateschangeovertimeDailyMonthlyYearlySoilRespirationDiurnal–Overa24hourperiodSoilRespirationSoilRespirationSoilRespirationUnderhighsoilmoistureconditions,manybacteriatakeintoomuchwaterviadiffusion,orthemovementofasubstanceacrossthebacteria'scellmembrane.Thismaycausethecellmembranetolyse,orbreak,spillingthecellcontentsintothesoil.Thelysisofbacteriaallowsforaspikeinresourcesformanybacterialpredatorssuchasprotozoans.ThisrapidincreaseinavailablelabilesubstrateswillcauseshorttermenhancedsoilrespirationSoilRespirationSpatialvariabilityUndernaturalconditionssoilfluxratescanvaryhugelybetweensites1or2metersapartSoilRespirationSpatialvariabilitySohowmanychamberswillIneed?SoilRespirationSpatialvariabilityGotothefieldwithasoilsurveytypesystemandtakeasmanymeasurementsaspossibleSoilRespirationSpatialvariabilityThemeanμ

=50TheStandarddeviationó=20TheCoefficientofvariationCv=ó/μ=20/50=0.4Generallyexpressedasapercentagee.g.40%SoilRespirationSpatialvariabilityN>or=(2XCv/error)2Where:N=numberofsamplesCv=CoefficientofvariationError=samplemeandeviationCVvaluesformostsoilsbetween10–50%Forexample,fora30%=CvToachievea10%errorN=(2x30/10)2=3636stationsormorewillgivea10%errorToachievea20%errorN=(2x30/20)2=9stationsSoilRespirationACEAutomatedSoilCO2ExchangeSystemSoilrespiration:asignificantgrowthareaofenvironmentalresearch

Onlylimitedfieldresearchuntilrecently.Significantincreaseinsoilrespirationsalesandinterestinlast2-3years.

(SoilchambersforLCi,LCpro+,ADC2250)Politicalinterest=Funding=ResearchAutomatedSoilCO2ExchangeSystemACELong-termunattendedmonitoringofsoilflux-Days/weeks/monthsRepeatedmonitoringofsameareaofsoilThenautomaticallyexposessoilaftermeasurement-AmbientconditionstosoilareabetweenmeasurementsUsersetsexperimentaltimesUnique“swingingarm”mechanism-ReliableandfieldruggedAutomateddesigncoverssoiltotakemeasurementIntegralCO2analyserinsidesoilchamber+Fastresponse+Nogashangupsinlonglengthoftubing+Easiertosetup+FieldrobustNoanimalseatingtubing+Nolargepumps=

powerefficient+MajoradvantageofACE0-1000ppmCO21ppmresolutionCompleteSystemorStationSoilchamberwithcollarSwingingarmControlconsoleFullyintegratedFullyindependentmeasurementStationnoPCorPDArequiredRobustfieldStationNolonglengthofgastubingGashangupsAnimaldamageReliableautomatedmechanismPowerefficient40Ahcarbattery–28days

WeatherproofdesignConsolecoverwaterproofconnectionsTransportable(7Kg)AvailableasclosedoropensystemClosedsystemChamberclosesMeasurementonetakenUpdatesmeasurementsevery10seconds(CO2rises)Untilendofexperiment(customerset)TimeCO2concentrationNCERcalculatedClosedsystemmode2.6Llargechamber+Measurementsarequickandsimple(5-10mins)+Mostpopular-Canbelessaccurate-StationisclosedsystemonlyOpensystemmodeOpensystemBeforechamberclosedreferenceairismeasured

Chamberclosed,measurementsevery10secondsCO2risesuntilequilibriumreachedUntilendofexperiment(customerset)TimeCO2concentrationNCERcalculatedRefOpensystemmode1Lchamber

+Potentiallymoreaccurate+StationcanbeusedinclosedmodeClosedchamberMeasurementsmorecomplexandslower(15-20mins)Zero/ambientoptionChangeingascircuitallowsambientCO2concentrationtobemeasuredMoreaccurateNCERInnetworknoteveryStationneedsambientoptionAmbientcanbemanuallyenteredTransparentchambersSoilonlySoilandsmallplantsSoilfluxNCEROtherACEStationsensorsPARLCi/LCpro+Siliconphotocell0-3000umolesSoilMoistureConnectupto4asstandardCommoncommercialsensorsDelta-TandDecagonSoilTemperatureConnectupto6asstandardThermistors(ADCsupply)ThermocouplesEasytosetupandprogramNogascircuitsetupbetweenanalyserandchamberControlconsoleLargedisplayscreen5keysonlyMenudrivensoftware(likeLCi)ProgramMode(open/closed)Period(timebetweenmeasurements)Flowrate(inopensystem,100-500ml/min)

Chambervolumeanddiameter(known)

Height(fromsoilinopensystem)

EndofexperimentBytimeDeltaCO2

LogfileACEStationdisplaysandrecordsGasexchangedatappmmmolesSoilfluxcalculations(NCER)OthersensordataDatastorageInterchangeableCompactFlashcards

Inconsole1Gcard=4,000,000datasetsMeasurementevery15minutescardcapacity114years!ACEStationconfigurationOpenorClosedSystemMetalortransparentchamberOptionalambientreadingTemperaturesensorsSoilmoisturesensorsUpgradesensornumbersSpareconnectorsLi8100Introduced2004Separatechamberandanalyser2MoftubingawayNotcapturedmarketWateringressDataerrorsExpensive(US$20,000persystem)ThecompetitionACEStationadvantagesovertheLi8100

Fullyintegratedsystem–Separateanalyser/chamber.NeedsPC/PDA

Analyserinchamber–

Analys