Direct Measurement of Oxygen Profiles and Denitrification Rates in Soil Aggregates1英文

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1、DirectMeasurementofOxygenProfilesandDenitrificationRatesinSoilAggregates1ALANJ.SEXSTONE,NIELSPETERREVSBECH,TIMOTHYB.PARKIN,ANDJAMESM.TiEDJE2ABSTRACT1985).Anaerobicmicrositeswithinsoilaggregateshavebeeninvokedtoexplainthisobservation(Greenwood,AnoxygenmicroelectrodewasmodifiedtomeasureO2concen-1

2、961;Currie,1961).Thesemicrositesarethoughttotrationsinwetaggregatesofasiltloamsoil.ThemicroelectrodetiphadanO2-permeabIemembraneopening3ionindiameter,andO2occurwhenO2consumptionexceedsdiffusivesupply.measurementscouldbemadeinaslittleas0.1-mmincrementstoaThevolumeofthesemicrositeshasbeencalculat

3、eddepthof12mm.Whenaggregateswereincubatedinair,steepO2assumingradialdiffusion,anaverageaggregateres-gradientsusuallyoccurredoververysmalldistancesfromtheag-pirationrateandanestimatedintra-aggregateO2dif-gregatesurface.Thesmallestaggregateexhibitingananaerobiccen-fusioncoefficient.Thesecalculati

4、onshavebeenin-terhadaradiusof4mm,althoughsmallaggregates(radius<6corporatedintorecentmathematicalmodelsinmm)weregenerallyoxic.Largeraggregates(radius>10mm)oftenattemptstopredictsoildenitrificationrates(Smith,hadmeasureableanaerobiccenters,withtheexceptionofthosefrom1980;Leffelaar,1979;McGilleta

5、l.,1981).anativeprairiesoilwhichexhibitedirregularO2profilesandhadDirectdemonstrationoftheoccurrenceofanaero-aerobiccenters,apparentlyduetoO2intrusioncausedbyoldrootbicmicrositeshasnotbeenpossibleduetothelackchannels.Oxygenprofilesobtainedin45degreeincrementsaroundofatechniquewiththenecessarysp

6、atialresolutiontoanaggregatecircumferencewereusedtoconstructcontourmapsofmeasureO2concentrationsoververysmalldistances.O2concentrationswithintheaggregate.OxygengradientswereOxygenelectrodeshaveprovidedthemostsuitablesomewhatasymmetric,suggestingnonuniformlydistributedsitesofapproachtothisproble

7、m.Oxygencanbeelectrochem-O2consumption.Anaverageintra-aggregateO2diffusioncoefficienticallyreducedonagoldorplatinumelectrodesurfaceof8.5X10"'cm2•s~'wasmeasuredforwater-saturatedaggre-thatisnegativelychargedat0.6to0.8Vrelativetogat