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Temporal Variability in Soil CO2 Emission in an Orchard Forest Ecosystem

By Hector Lopez,2014-08-05 21:26
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Temporal Variability in Soil CO2 Emission in an Orchard Forest Ecosystemin,an,CO,Soil,CO2,soil

    Temporal Variability in Soil CO2 Emission

    in an Orchard Forest Ecosystem Pedosphere18(3):273283,2008

    ISSN1002-0160/CN32?-1315/P

    ?2008SoilScienceSocietyofChina

    PublishedbyElsevierLimitedandSciencePress

    PEDOSPHERE

    WWWelseviercom/locate/pedosphere

    TemporalVariabilityinSoilC02EmissioninanOrchard

    ForestEcosystem1

    LIYueLin,D.OTIENO,K.OWEN,ZHANGYun,v,J.TENHUNEN,RAOXing

    Quanand

    LINYongBiao

    SouthChinaBotanicalGarden,ChineseAcademyo/Sciences,Guangzhou510650 .Departmento/PlantEcology,Universityo/Bayreuth,95440Bayreuth(Germany) .Schoolo/ResourcesandEnvironmentalScience,HubeiUniversity,Wuhan430062 (ReceivedAugust22,2007;revisedJanuary26,2008)

    ABSTRACT

    (Chin.E-Maihyuelin@qcbg.accn

    (China

    TemporalvariabilityinsoilCO2emissionfromanorchardwasmeasuredusingadynamicopen-chambersystemfor

    measuringsoilCO2effiuxinHeshanGuangdongProvince.inthelowersubtropicalareaofChina.Intensivemeasurements

    wereconductedforaperiodof12monthsSoilCO2emissionswerealsomodeledbymultipleregressionanalysisfrom

    dailyairtemperature,dry

    bulbsaturatedvaporpressure,relativehumidity,atmosphericpressure,soilmoisture,andsoil temperature.Datawasanalyzedbasedonsoilmoisturelevelsandairtemperaturewithannualdatabeinggroupedinto

    eitherhot

    humidseasonorrelativelycoolseasonbasedontheprecipitationpatterns.Thiswasessentialinordertoacquire

    simplifiedexponentialmodelsforparameterestimation.MinimumandmaximumdailymeansoilCO2effiuxrateswere

    observedinNovemberandJuly.withrespectiveratesof1.98O.66and11.O4

    O.96ttmolm2s-beingrecorded.

    AnnualaveragesoilCO2emission(FCO2)was5.92#molms

    .Includingalltheweathervariablesintothemodel

    helpedtoexplain73.9%oftemporalvariabilityinsoilCO2emissionduringthemeasurementperiod.SoilCO2emux

    increasedwithincreasingsoiltemperatureandsoilmoisture.PreliminaryresultsshowedthatQ10,whichisdefinedas

    thedifierenceinrespirationratesovera10.Cinterva1.waspartlyexplainedbyfinerootbiomass.Soiltemperatureand

    soilmoisturewerethedominantfactorscontrollingsoilCO2emuxandwereregardedasthedrivingvariablesforC02

    productioninthesoil.Includingthesetwovariablesinregressionmodelscouldprovideausefultoolforpredictingthe

    variationofCO2emissioninthecommercialforestsoilsofSouthChina.

    KeyWords:CO2emission,lowersubtropicalarea,orchardforestecosystem,soilmoisture,soiltemperature

    Citation:Li,Y.L.,Otieno,D.,Owen,K.,Zhang,Y.,Tenhunen,J.,Rao,X.Q.andLin,Y.B.2008.Temporalvariability

    insoilCO2emissioninanorchardforestecosystem.Pedosphere.18(3):273283.

    INTR0DUCT10N

    SoilCO2emissionisoneofthemajorpathwaysbywhichC02fixedbyterrestrialplantsisrelea

sed

    backintotheatmosphere.RecentstudiesemphasizethesignificantcontributionofsoilCO2emissions

    totheatmosphericCO2pool(RaichandPotter,1995;SchlesingerandAndrews,2000;Wangeta1.,

    2002;Chriseta1.,2005).Therefore,understandingthetemporalvariabilityinCOzexchangeinforestry,

    agricultureandnaturalsystemsisasignificantsteptowardsunderstandingtheglobalCOzexchange

    cycle.Environmentalvariablessuchassoiltemperature.soilwatercontent.airtemperaturephotosyn-

    theticallyactiveradiation(PAR)andairhumiditysignificantlyaffectecosystemCOzexchange(Lloyd

    andTaylor,1994;Davidsoneta1.,1998;Liueta1.,2006).Soilmoisturedeficit,forexample,decreases

    rootrespirationbvupto17%(Burtoneta1.,1998).Gouldeneta1.(1996)reportedahigherdecrease

    inheterotrophicrespirationascomparedtoautotrophicrespirationduringanextendeddroughtina

    temperateforest.AnotherfactorthatsignificantlyaffectssoilCO.emissionissoiltemperature.Sea-

    ProjectsupportedbytheNaturalScienceDoctorialFoundationofGuangdongProvince,China(No.4300613),the

    NationalNaturalScienceFoundationofChina(No.30200035),theChineseEcosystemResearchNetwork(CERN),anda

    postdoctoralfellowshipfromtheMinistryofEducationofthePeople'sRepublicofChina.

274Y.L.LIe0f.

    sonalvariationsinsoilrespirationhaveoftenbeenassociatedwitheitherchangesinsoiltemperature

    fAnderson,1973;Fangeta1.,1998:Daniel,2004)orchangesinbothsoiltemperatureandsoilwater

    contentfDavidsoneta1.,1998:Eproneta1.,1999;qiandXu,2001).

    EmpiricalrelationshipsbetweensoilCO,effluxe8andenvironmentalvariablesincludingsoiltem-

    perature.soilwatercontentandthecoarsemineralsoilfractionshowthateffiuxincreasesexponentially

    withtemperaturewhensoilmoistureorotherfactorsarenotlimiting(Bunnelleta1.,1977;Nakane{

    1994:Hansoneta1.1993:RaichandSchlesinger,1992;Reichsteineta1.,2003).Difierenttypesofmodels

    usingtemperaturetimeequivalence(FengandLi,1997;FangandMoncrieffj2001)consideratmospheric

    climatevariablesasthemainfactorsgoverningtemporalvariabilityofsoilC02exchangeinthelong

    andshorttermintervals.Thus,C02exchangeinsoil.vegetation

    atmospheresystemsarebothdirectly

    andindirectlyassociatedwithmeteorologicaleventsjsuggestingthatmeteorologicaldataalonecould

    explainasignificantportionofthetemporalvariabilityinC02emissionfrombaresoils(LaScalaeta1.j

    2003).MassmannandFarrier(1992);OuyangandZheng(2000)andJassaleta1.(2004)suggestthat

    solarradiationandatmosphericpressurearethemainvariablescontrollingsoilCO2productionrates

    andtransportandhenceCO2emissionintotheatmosphere.

    InformationisscantonsoilCO9emissionanditsregulatorymechanismsinChlneseforests.parti

    cularlyfororchards.whichcoverlargeareasofSouthChina.InGuangdongProvinceofSouthChina,

    orchardsarewidelyestablishedasamaoreconomicactivityandtheareainuseasplantationsissig

    nificantlyandsteadilyontheincrease.Forexample.between1979and2003theareaundercommercial

    orchardsystemsincreasedmorethantenfold.Outofthe9.33×10haforestedland.9.73×

    100ha

    iscoveredbyorchardplantations.Itisnotclearyethowthetransformationofnaturalforestsystems

    intoorchardsinfluencessoilfunctioningandtheoverallecosystem.BecausesoilCO2emissionsarevery

    sensitivetoagriculturalactivities(Huangeta1.j2002;Peng,2003)jitisimperativethatC02emissions

    ontheselandsareevaluatedanddocumented.Theobectivesofthisstudyweretoi)monitortemporal

    variationofCO2effluxincommercialforestsofSouthChinaandii)modelthetemporalvariabilityof

    soilCO9effluxintermsofphysicalenvironmentalfactorsanddevelopsimplifiedmodelsfordescribing

    soilCO9fluxesinthecommercialforests.

    MATERIALSANDMETH0DS

    Sitedescription

    ThestudywasconductedattheHeshanInterdisciplinaryResearchStation(1l2.54E,22.4lN), ChineseAcademyofSciences.inGuangdongProvince.China.Theexperimentalsiteliesinanarea

    withlowhillsfpeakelevationof98m)andsmallcatchmentsfeachhavinganareaofabout5

    8ha).

    Theclimateissubtropicalmonsoonwithameanannualprecipitationofl800

    2000mmfallingmainly

    fromApriltoSeptember.TheperiodfromOctobertoJanuaryisparticularlydry.Themeanannual

    temperatureis21.7.C.withmeanmaximumandminimumannualtemperatureof28.7and13.1.C

    occurringinJulyandJanuary.respectively.ThesoilisanOxisoldevelopedfr-OIIlsandstone.withapH

    ofabout4.0.SomesoilpropertiesarelistedinTableI.

    TABLEI

    Somepropertiesoftheorchardsoilunderconsideration

    )FromLieta1.

    (2002)

SOILCO2EMISSIONINORCHARDFOREST

    Experimental

    275

    Sixadjacentcatchmentscoveredonlyingrasseswithatotalestimatedareaof21.59hawerechosen

    forinvestigationsin1984.basedontheirsimilaritiesinsoil,vegetation.slopeandelevation.Adifferent

    foresttypewasrandomlyallocatedtoeachcatchmentandtreeswereplantedona2.5m×

    3mgridfLi

    e

    (a1.,2000,YuandPeng,1995).FivecatchmentscomprisingsinglespeciesstandsofAcaciamangium,

    Acaciaauriculaiformis,Eucalyptuscitriodora,Pinuselliotii,Schimasuperbaandonecatchmentofan

    agroecosystemalongnaturalwatershedswereestablishedin1984.Theagro

    ecosystemcatchmentwas

    approximately3.55haof"forestorchardgrassbelt

    fishpond".Thisisatypicalorchardfclrestmodelof

    SouthChina.Whenthisstudycommencedattheagro

    ecosystemforchard1plotin2001thefruittree

    speciesontheplotwereLitchichinensisSonn.,DimocarpuslonganLourandnraindicaL.with

    anaverageageof5years.Thecanopyclosurewas40%

    50%.Theunderstoryismainlycomprisedof

    PennisetumpurpureumSchumach.,PaspalumconjugatumBergius,/schaemumaristatumLinn.,Setaria

    faberiiHerrm.,AgeratumconyzoidesL..mosapudicaL.andAeschynomeneindicaL. Microclimate

    Airtemperature(ir),dry

    bulbsaturatedvaporpressure,relativehumidity,atmosphericpressure andsoiltemperaturewerecontinuouslyrecordedusingamicro

    meteorologicalstationestablishedon

    theexperimentalsite(VaisalaM520,Helsinki,Finland).Datawererecordedevery30seconds,averaged

    andloggedevery30minutes.SoilmoisturestatuswasdeterminedusingMPKitvolumetricsoilmoisture

    sensor(ICTInternationalPryLtd.,Armidale,NSW,Australia)installedata5cmdepth. SoifC02emissionmeasurements

    CO2emissionsweremeasuredoneachplotduringa12

    monthstudyperiodstartinginFebruary

    2001.Oneachmeasurementday.hourlymeasurementsweretypicallyconductedfrom6:00a.m.till

    8:00P.m.Measurementswereconductedeveryfourthweekoverthecourseoftheyear.Tocapture

    thetemporalvariabilityinsoilCO2emissiononshortandlong

    termscales,asamplingsystemwas

    constructed,whichwascapableofcontinuouslyrecordingtheinstantaneouseffiuxratefrommultiple

    samplingpositionsusingtheLicor6200gasexchangesystem(LI

    CORInc.,Lincoln,USA).TheCO2

    fluxchamberisanopendynamiccylindricalsystemwithanelectricfaninsidetomaketurbulence.The

    chamberismadeofstainlesssteelandhasadiameterof0.25mandaheightof0.35m.withanopen

    bottomend.

    ThreeplotswithintheorchardwerechosenforCO.emissionmeasurementsinthreedifferentaspects

    (E,wandN)alongtheslopeandeachplotwasreplicatedthreetimes.Collars(withopenends)were

    installed2daysbeforethesamplingdatesateachoftheplots.Collarswereinserted5cmdeepinto

    thesoil.with50cmspacingateachofthemeasurementplots.AUcollarswerepositioned2

    3meters

    awayfromthetrees.Withineachcollar.allabovegroundpartsofthevegetationwereremovedtwoor

    threedaysbeforemeasurementsweremade.RecordsforsoilC02emissionsineachplotweretaken

    forapproximately120sat8

    30sintervalsdependingontheincrementoftheC02concentration.

    Normally,3pmolmol

    wasnecessarysothattheCO2differentialsignalwasstableandensuredthat theconcentrationchangesinthechamberduringthiscyclingtimewerecapturedbyanalyzer,andalso

    thatsoiltemperaturevariationsinthechamberduringmeasurementswereminimized. Rootbiomasssampling

    SoilsampleswerecollectedadayafterCO2measurementsat0

    20cmdepthfromeachoftheplots

    usingasoilcorerwith5cmdiameter.Finerootswereextractedbywashingthesampledsoilmasses,

    usingsievestofreetherootsfromsoil.Liverootswithadiameterlessthan2mmwerethenoven

dried

276

    at70.Cbeforeweighing

    Statisticalanalysisandcalculation

    YL.LIet0f.

    TheC09emissionresultsandallthemicroclimatedataweresubjectedtodescriptivestatisticsand

    stepwiseregressionanalysis(SPSSInc.,1999;LaScalaeta1.,2003).Thesoilfluxwasfittedintothe

    modelasthedependentvariableandtheenvironmentalfactorswerefittedastheindependentvariables.

    Initially,allthemeteorologicalfactorswerefirstcombinedtoexplainthevariationsinsoilC0,emission.

    Then,basedontheresultsfromstepwiseregressionmodel,thedeviationsoftheserelativelycomplex

    relationshipswereassessed.Simplemodelswithsoiltemperatureandsoilmoisturewereperformed.

    Fourexponentialequationswereused:

    s.il1=ke.T

    s.il1=ke.Te

    (1)

    wheres0iJ)isthesoilrespiration(mmolCO2ms-1),Tisthesoiltemperature(.c),0isthesoil moisture(m.m.),and,a,bareconstantsfittedtotheregressionequation.

    soil1

    s.il1

    /~refe(

    RrefeE~(东【_

    1

    Zl

l

    r

    )

    )SWC

    SWC+

    whereEq.3istheclassicfunctionasdescribedbyLloydandTaylorf19941andEq.4isamodified

    versionofEq.3Tref(.C)isthereferencetemperature,To=-46.02.C,iristheairtemperature, isaconstant,andSWCisthesoilwatercontent.Rrpf(#molms)isthesoilrespirationunder standardconditionsandE0istheactivationenergytypeparameter.

    TheindexofsoilrespirationresponsetotemperaturewasalsodescribedbytheQ]0value,definedaN

    thedifierenceinrespirationratesovera10.Cinterva1.Q]0valuewascalculatedusingtheexponential

    relationshipbetweensoilrespirationandsoiltemperaturefBuchmann,2000:XuandQi,2001b1:

    Q1o=e..(5)

    whereaistheconstantfittedintoEq.1.

    Finally,basedonthefinerootbiomassmeasurements,wetestedtherelationshipbetweenthisbiotic

    factorandQ1ovalues.Allregressionfitswereperformedbyuser

    developedprogramsusingPVWAVE

    software,version7.51(VisualNumerics,Inc.USA).

    RESUISANDDISCUSSION

    Environmentallactors

    Fig.1showsrainfa11,temperaturesandglobalradiationpatternsintheHeshanInterdisciDhnarv

    ResearchStationfortheperiod2001and2002.ThedescriptivestatisticsofsoilCO2emission(FCO2)

    andabioticenvironmentalfactorvariablesobservedduringthestudiedmeasurementdaysof

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