SoilsandGlobalWarming:APositiveorNegativeFeedback?GlobalsoilshavealargeCpoolRatesofcyclingofthispoolindicatethattheycanaffect/respondtoatmosphericprocessesonannualtodecadaltimescalesOneoftheimmediateeffectsofhumaninducedglobalchangeiswarmingwillthatchangesoilC?VariationsoftheEarthssurfacetemperaturefor:(a)thepast140years4oal6e.lQE066T0一L96r6JZ-t-E0J=(OJ052-Esc一t18601880190019201940196019802000Year(b)thepast1,000years5050oooMl066Lo*atnEo上(0J3lruEeds!u-s包nuedeaNORTHERNHEMISPHEREData-fromthQrmoimQter&(red)andfromirerings,corals,c&caresandhistoricalrecords(blue).120014001600Year18001000IndicatorsofthehumaninfluenceontheatmosphereduringtheIndustrialEra(a)Globalatmosphericconcorrtraliomofthreowellmixedgreenhousegass360_Carbondioxide0.50.0_340宮320F30028Q260.1O.05.018002000G-UJAA)bup3(bAne一peCEJ554321-o1.QQQQooo5017103902o272501000120014001600Year(odd)ozuogelug。匸(l.liqsolu(b)SulphateaerosolsdepositedinGrwnlondice20g*B6uuolosEE)UOQB4UBQU03seud_ns(a)NaturalSimulatedannualglobalmeansurfacetemperatures(b)Anthropogenicmodelobservations5aoaooo2o59185Oo1(0S2-ELU0UBmEdiuJrt-510.o.5ao.o00250190019(0乙seEEOUccEnffi-CDdE一(c)AllforcingsgJSMEEOUean甩CIE一YearTheglobalclimateofthe21stcentury(a)CO2emissions5050522110吉4e】stMEalDGJ&ScmaiosA1BA1TA1RA2H1B2t3a20002020If:-1Bn-VeraIJ.50850.1WUd|SfivarHnTiiahdlBRES2000202020402060200021WY&ar(d)TemperaturechangeBFEI4Oan-M-JBdLUQF-htetiansanttarSoBarsshowtvmn护n2100sajnlmMs(e)SealevelriseFigure5:Theglobalclimateofthe21stcentury刊illdependonnaturalchangesandtheresponseoftheclimatesystemtohumanactivities.SoilCandTemperaturedC/dt=I-kC-Virtuallyallstudiesshowitwill(atleastonshortterm)-Microbesincreaserates,decomposethemostreadilyaccessableCmaterials(andthereforeincreaseCO2losses)-LedtohighlypublicizedviewthatsoilswillexacerbateglobalCO2buildupduringwarming.newsandviewsRespirationinthebalanceJohnGraceandMarkRaymentModelsofhowforestswillrespondtoclimatechangeusuallyassumethatcarbondioxideoutputfromdecomposingorganicmatterwillincreasewithglobalwarming.Thatassumptionmaybewrong.Eachyeartheworldsvegetationabsorbsabout60billiontonnesofcarbonbyphotosynthesisandreleasesasimilar一butnotexactlyequivalent一amountbyrespiration1.Theseiluxesofcarbonarelarge,dwarfingthe6.5billion,tonnesemittedbyfcosysten?iypCartonpfoducibn(gx70Forest23.25Savannah18.61Temperategrassland4.39Tundraarcticalpino0.95Ltesertands&midesatscrub1.35temperatureareactiveformostoftheyear.Inmoresoutherlylatitudes,bycontrasttliemicrobesbecomeinactiveformuchoftheyearwhenthesoilisdry.Orperhapsthemorenortherlyecosystemscontainmuchcarbonasorganicmatierwhichhasaccumu-Thecontrastbetweenrateandtotalrespiration-respirationmustbenormalizedtotheamountofreactantavailabletemperatureResultingsoilrespirationratesNevadaSoilsasGuidetoClimateResponseFig.*1.Estimatesofturnovertimeforlow-density“ndhydrolyzabtecarbonfractionsderivedfromtheobservedincreasein14Cbetween1959and1992(19).(A)ChangesinA,4Cvaluesobservedintheatmosphere,comparedtothechangein114Cvaluesexpectedinsteady-stateSOMreservoirswithturnovertimesof20or70years(79).Double-headedarrowsshowtheA(A14C)values.(B)1(A14C)expectedforfast-cyclingcarbonwrthdiflerentturnovertimes(79).(C)Tumovertimesforbwlensityorganicmatterfractions,assumingthat1010%ofthecarboninthelov/-densityfractionsispassive.UncertaintiesinturnovertimeARderivedfromtheoverallaccuracyofheradiocarbonmeasurementabout12permilinA(A,4C)areofsimilarmagnitudetouncertaintiesintheamcxjntofpassivecarbon.(D)HydrolyzabledenseorganicmatterfractionturnovertimesdonotshowacleartrendwithaltitudeErrorbarsshowtherangeofturnovertimescalculated,assuming0%passivecarbonmthisfraction(slowerturnover)andassumingtheamountofpassiveorganicmatterneededtoexplainarchivedA14Cvaluesforthisfraction(79):MAT,meanannualtemperature-1*.田StanaI7TI、0*620604080A0120B804000102030Meanannualtemperature(C)Fig.2.(A)Turnovertimesforfast-cyclingfractionsoflow-densitycartoonintheupper20cmofsoilfromtheSierraNevadatransect(thisstudy).Hawaii(7).andeasternAmazonia(2223).Theexponentialcurvefit(with95%confidenceintervals)isinthe1950snrulshowlirtleornoincreaseinAl4Csince1963.Withtheuseofthesecriteria,thelow-densityfractionhastheshortest,andthenonhydrlyzabledenseresiduethelongest*averageturnovertime(Table1).ToquantifyturnovertimesforSOMfractions,wecomparedtheobservedincreaseinAl4Cbetween1959and1992(definedasA(AHC)|withrheincreaseprodietedwithacimc-dcpcnJcrumodel(19)(Fig.1).ThisapproachassumesSOMhasremainedatsteadystateoverthepast30yearsWebelievethisistrueforSierratransectsitesIxrcausclandusetherehasnotchangedduringthistime(20)andthecar-year1(9)|.WethereforeconcludethattheturnoverruneofrheShaverlowcarbonis57years(Fig.1C).Althou