植物營養(yǎng)元素的土壤化學3-土壤中的C(上)

第二章土壤碳素循環(huán)及調(diào)控Chapter2CarboncyclesinSoilLowcarboneconomyGHGs=greenhousegasesIPCC=IntergovernmentalPanelonClimateChange

（政府間氣候變化專業(yè)委員會）“哥本哈根氣候會議”Fig.Deviationsfromrecentexponentialincreasesinfossilfuelburning(Bacastow&Keeling,1974)Theindustrialrevolution,whichstartedaround1750,drivenbycheapandeasyaccesstomodernenergythroughfossilfuelcombustion,ledtomassproductionofmodernamenitiesatlowcost.Indeedallavailedamenitiesbyindustrializedsocietiesarebasedonfossilfuelderivedenergy.Thus,themoderncivilizationcanbeappropriatelytermed“theCarbonCivilization”ortheC-Era(Lal,2007),ascomparedwiththehistorichydriccivilizations,whichthrivedinthevalleysofTigris,Euphrates,Nile,Indus,Huangetc.Indeed,theworldenergyconsumptionincreased40timesbetween1850and2005.TheatmosphericconcentrationofCO2hasincreasedfrom280ppmvsincethelate1700stoabout380ppmvin2006,ispresentlyincreasingattherateof1.8ppmvyr?1or0.47%yr?1(WMO,2006.)政府間氣候變化專門委員會(IPCC)第三次評估報告（2001）二十世紀全球平均氣溫上升0.60.2C;從1861年以來，二十世紀九十年代是最熱的10年，其中，1998年是最熱的一年;在過去的一千年中，二十世紀是最熱的一個世紀;從1950年到1993年，陸地夜間日平均氣溫每10年升高約0.2C，白天升高約0.1C。海面氣溫升高約為陸地的一半.海平面上升；降水分布發(fā)生變化；沙漠化加??；自然災害發(fā)生頻繁增加。全球變暖的后果?HumanpopulationSizeResourceuseHumanenterprisesAgricultureIndustryRecreationInternationalcommerceLandtransformation

LandclearingForestryGrazingIntensificationBioticadditionsandlosses

InvasionHuntingFishingGlobalbiogeochemistry

CarbonNitrogenWaterSyntheticchemicalsOtherelementsClimatechange

EnhancedgreenhouseAerosolsLandcoverLossofbiologicaldiversity

ExtinctionofspeciesandpopulationsLossofecosystems改進能源結構提高能源效率植樹種草，增加生態(tài)系統(tǒng)對CO2的吸收如何減少溫室效應氣體的排放?Csequestration(碳固定)CarbonsequestrationimpliesthenetremovalofCO2fromtheatmosphereintolong-livedpoolsofC,suchasterrestrialandgeologic.Inotherwords,itiscapturingandsecurelystoringCbybioticphotosynthesisandabioticinjectionintogeologicstrataoroceanprocesses.LalR.SoilSci.Soc.Am.J.2007,71:1425–1437Carbonsequestration1997年12月，面對環(huán)境惡化，氣候變暖，在日本京都舉行的聯(lián)合國氣候大會通過了《京都議定書》，目標是在2008年至2012年間，將發(fā)達國家CO2等６種溫室氣體的排放量在1990年的基礎上平均削減5.2％。為了使議定書真正發(fā)揮作用，協(xié)議規(guī)定，只有在占1990年全球溫室氣體排放量55％以上的至少55個國家批準后才能生效。京都議定書（Kyotoprotocol）Theindustrialemissionsofcarbon(C)inChinaareabout1Pgyr-1,secondonlytotheUnitedStatesestimatedat1.84Pgyr-1for2000.Becauseofthedifferencesinpopulation,however,thepercapitaemissionis0.08Tgper100000inhabitantsinChinacomparedwith0.55Tgper100000inhabitantsintheUnitedStates(NET,1998).Withitsrapidlyincreasingeconomy,however,ChinamaysurpasstheUnitedStatesastheworld’slargestemitterofCby2020.LalR.LandDegrad.Develop.13:469–478(2002)我國2001年的工業(yè)CO2排放為1Pg/yr，僅次于美國（1.84Pg/yr），預計在2005年會超過美國,達到2Pg/yr，我國面臨著減排的巨大壓力。這是一個關系國家環(huán)境外交和農(nóng)業(yè)可持續(xù)發(fā)展的食物安全與環(huán)境安全保障的重大問題。黃耀.第四紀研究.2006按照IPCC第2次評估報告提供的全球增溫潛勢數(shù)據(jù)計算,1994年中國溫室氣體總排放量為36.50×108tCO2當量,其中CO2,CH4和N2O分別占73.1%,19.7%和7.2%。能源活動是中國CO2排放的主要來源,占90.95%；農(nóng)業(yè)活動和能源活動是CH4排放的主要來源，分別占50.15%和27.33%；農(nóng)業(yè)活動是N2O排放的主要來源,占92.4%。About20%oftheglobalemissionpresentlycomefromlandusechange(IPCC,2001)Agriculture’sContributiontoClimateChange–SternReviewAgriculture=14%ofglobalGHGsLanduse(deforestation)=18%ofglobalGHGsSource:SternReview:theEconomicsofClimateChangeAgriculture’sContributiontoClimateChange–SternReview38%38%13%11%Globalsourcesofnon-CO2emissionsfromtheagriculturesector(2000)Source:SternReview:theEconomicsofClimateChangeHillelD.2008Agricultureaccountsforasizableshareofnon-CO2emissions,includinganestimated47%ofCH4andasmuchas84%ofN2O.UKAgriculture-SomeKeyFactsOnly0.5%ofGDP(agri-foodsector7%)1.7%ofemployment(agri-food14%)Manages70%ofEngland’sland(80%ofruralland),withhugebenefitsforlandscape,biodiversityandaccessBut…contributes7%oftheUK’sGHGemissions(37%ofmethane,63%ofnitrousoxide)…andMajorityofnitrateemissionstowaterandammoniaemissionstoairJeremyEppel,DeputyDirector,Food&FarmingGroup,Defra全球氣候變化簡史不同的聲音.“氣候變化問題的非主流思考：事實與邏輯”,科學時報,2009年8月11“哥本哈根鬧劇后的沉思”,科學時報,2010-02-11氣候問題的“郵件門”

(2009年11月)英國東英吉利大學氣候研究中心上千封電子郵件和3000多份有關氣候變化的文件被曝光，這些文件顯示：這些氣象學家利用各國政府對氣候變化問題的關心，用一些不實數(shù)據(jù)制造氣候變暖的假象，營造恐慌心理，然后從政府或其他機構手中騙得了更多的科研經(jīng)費。氣候問題的“冰川門”事件IPCC在2007年發(fā)布的第四次評估報告中寫道“喜馬拉雅冰川的消融速度超過了世界其他地區(qū)的冰川，如果全球變暖的速度持續(xù)下去，喜馬拉雅冰川在2035年甚至更早前消失的可能性非常高”。客觀對待IPCC的報告美國250余名科學家聯(lián)名上書呼吁不要指責IPCC荷蘭250余名科學家聯(lián)名問題與對策:我國已成為全球最大的溫室效應氣體排放國，面臨著減排的巨大壓力。丁仲禮,段曉男,葛全勝,張志強.2050年大氣CO2濃度控制:各國排放權計算.中國科學，D輯，2009，39(8):1009-1027文章提出了“人均累計排放指標”的概念，以體現(xiàn)“共同而有區(qū)別的責任”原則和公平正義準則。設定2050年前將大氣CO2濃度控制在470ppmv的目標,以1900年為時間起點,對各國過去(1900-2005年)人均累計排放量、應得排放配額以及今后(2006-2050年)的排放配額做了逐年計算.全球碳循環(huán)概況土壤碳庫在全球碳循環(huán)中的作用土壤碳的不同組分及其特性土壤碳庫的調(diào)節(jié)TableDistributionofCinsomeofthemaincompartmentsintheearth(Delwiche)CompartmentAmountofC,×1012kgAtmosphere700Soilorganicmatter(to2mdepth)2500Landlifeforms480Marinehumus3000Oceanlifeforms50Dissolvedcarbonate-bicarbonateinoceans3840Coalandpetroleum1×104

Sediments6×107

StevensonFJ,1986(1)全球碳分布全球碳循環(huán)概況FigThecarboncycle(Numbersarestorageas1015gorfluxesas1015gperyear)Ecology,ManuelCM,2002為了維持全球碳平衡，其焦點不是各個庫的碳貯存總量，而是每年碳的去處和動態(tài)變化問題?！霸础迸c“匯”

(sourceandsink)把釋放二氧化碳的庫稱為“源”，吸收二氧化碳的庫稱為“匯”。PaulEA,2007(2)全球碳循環(huán)

SoilOceanBiotaAtmosphereTerrestrialphotosynthesisRivertransportoforganicmatterandcarbonatesRespirationCarbonateinputCO2exchangeLitterandrootinputCalcificationMarinerespirationMarinephotosynthesisTheshort-termCcycle人為因素對碳循環(huán)的干擾作用(單位Pg/年）大氣土地海洋沉積物礦質(zhì)有機碳碳酸鹽地質(zhì)庫5.4礦質(zhì)燃料燃燒5.3水泥生產(chǎn)0.1土地利用變化1.7土地吸收1.9海洋吸收1.9PostWM,etal.,BioScience?2004，54(10)Fig.1.IllustrationofthemainstoresandflowsofCinacropland,showingthreepoolsofsoilCforsimplicity,thoughrecognizingthatsoilCspansacontinuumofforms.(Janzen,2006,SBB)2.土壤碳庫在全球碳轉化及循環(huán)中的地位LalR.Science,2004Theglobalsoilcarbon(C)poolof2500gigatons(Gt)includesabout1550Gtofsoilorganiccarbon(SOC)and950Gtofsoilinorganiccarbon(SIC).ThesoilCpoolis3.3timesthesizeoftheatmosphericpool(760Gt)and4.5timesthesizeofthebioticpool(560Gt).(1)土壤碳庫的意義AtmosphericCpool(760Pg)TerrestrialCpool2860PgSOC=1550Pg(to1mdepth)SIC=750PgBiota=560PgFigure1.Cycleof

Cin

terrestrialecosystemandtheatmosphere.PhotosynthesisPlantandsoilrespirationLalR.Science.2004,304土壤碳庫的穩(wěn)定、增長或釋放與大氣庫的變化有重要的關系，土壤能否增加碳儲存是關乎陸地生態(tài)系統(tǒng)凈碳匯飽和問題的重要理論基礎，這一問題已成為土壤與全球變化研究的重點和熱點科學問題。SequestrationofCinsoils

isoftenseenasa‘win-win’proposition;itnotonlyremovesexcessCO2fromtheair,butalsoimprovessoilsbyaugmentingorganicmatter,anenergyandnutrientsourceforbiota.LalR.SoilSci.Soc.Am.J.2007,71:1425–1437LalR.SoilSci.Soc.Am.J.2007,71:1425–1437土壤的“Csinks”、“Csequestration”、“Cstorage”、“Cstabilization”及“Cstoringcapacity”(2)土壤碳貯量(Cstorage)土壤碳貯量的計算？土壤碳貯量=土壤容重×土壤有機碳含量×土壤體積Soilorganiccarbon=1550PgSoilinorganiccarbon=750PgYu,D.,etal.,RegionalpatternsofsoilorganiccarbonstocksinChina.JournalofEnvironmentalManagement(2006),Yu,D.,etal.,RegionalpatternsofsoilorganiccarbonstocksinChina.JournalofEnvironmentalManagement(2006),SoilsinChinacoveranareaof9.281×106km2intotal,withatotalSOCstockof89.14Pg(1Pg=1015g)andameanSOCdensityof96.0tC/ha.中國是世界上平均土壤碳密度較低的國家。全球全土碳密度平均為121t/hm2，我國全土平均有機碳密度的報道值介于80～105t/hm2，均遠遠低于世界平均值。表中國和歐洲表層土壤有機碳密度比較(tC/ha)土地利用歐洲中國土地總計70.852.0耕地53.037.0潘根興，趙其國.地球科學進展.2005不同土地利用方式對土壤剖面碳貯量的影響TableLand-useeffectsondensityoforganiccarbon(kg/m2)in416soilprofilesofeasternChina(adaptedfromCai,1995)HorizonNaturalvegetationFuelforestUplandfieldsPaddyfieldsA5.402.171.312.40B6.582.680.921.44C2.271.671.642.94Total14.256.523.876.78LandDegradation&Development,2002,13:469-478植物體組成及分解轉化特性土壤有機碳的組分及特性土壤有機碳穩(wěn)定性的機理3.土壤碳的不同組分及其特性PlantlitterastheprinciplesourceofsoilorganicmatterformationPlantsarethemainsourceofcarbontosoilsthroughtissueresiduesorviarootexudatesandsymbioticfungi.陳興麗等表1黃土高原幾種植物殘體的化學成分植物殘體有機碳CTOC(g·kg-1)全氮NTotalN(g·kg-1)C/NRatios木質(zhì)素(%)喬木A榆樹422.5825.3616.6625.20B小葉楊414.449.0245.9730.89C刺槐437.7314.9229.3327.78灌木D檸條466.8530.9515.0829.59E沙棘464.7029.7115.6427.14F山桃458.5328.2916.2125.76草本G長芒草499.469.8650.6727.54H白羊草432.696.6165.4928.61I沙打旺427.9327.0115.8424.10J紫花苜蓿464.9832.7814.1924.47(C6H10O5)n+nH2OnC6H12O6C6H12O6+6O26CO2+6H2O+能量在通氣不良的情況下，可形成中間產(chǎn)物有機酸（丁酸）和甲烷、氫氣C6H12O6CH3CH2CH2COOH+2H2+2CO2+能量4H2+CO2CH4+2H2O碳水化合物的礦化有機物質(zhì)的礦化腐殖物質(zhì)形成的生物學示意圖

植物殘體

在微生物作用下轉化

糖

多酚

氨基化合物

木質(zhì)素分解產(chǎn)物

類木質(zhì)素

醌

醌

腐殖物質(zhì)

1234Firststage:StevensonFJ,1986StagesinthemicrobialdecompositionDecayofeasilydegradablesubstances.PartialconversiontoCO2andbodytissueSecondstage:Thirdstage:Fourthandsuccessivestage:Celluloseandothercarbohydratesutilizedwithfurtherweightreduction.Formationofnewbodytissue.Partofpreviousbiomassmineralized.Furtherdecreaseincellulose.Initiationoflignindecomposition.Furtherdecreaseinbiomass.Furthercycling.Forplantresidues,aboutone-thirdofthecarbonwillremaininthesoilattheendofthegrowingseason.陳興麗等圖1黃土高原不同植物殘體碳的礦化率C/NA榆樹16.66B小葉楊45.97C刺槐29.33D檸條15.08E沙棘15.64F山桃16.21G長芒草50.67H白羊草65.49I沙打旺15.84J紫花苜蓿14.19Fig.Influenceofleaftoughnessandnitrogencontentondecomposition(Gallardo&Merino,1993)Nitrogenmostoftencontrolstherateoforganicmatterdecomposition.(C/Nratio)圖1土壤植物生態(tài)系統(tǒng)中的碳、氮素轉化過程示意圖不同C/N比的植物殘體等土壤微生物量部分穩(wěn)定的有機氮

穩(wěn)定的腐殖質(zhì)態(tài)氮NH3,NO3-NH3,NO3-腐殖化作用施用肥料作物吸收CO2等釋放土壤中氮、碳協(xié)調(diào)是關鍵！有機物施入土壤的去向（1年后）：有機殘體（100）CO2（60-80%）土壤生物體（3-8%）非腐殖物質(zhì)（多糖、有機酸等）（3-8%）腐殖物質(zhì)（10-30%）腐殖質(zhì)SoilsinourEnvironment.1995TableThedecompositionofthedifferentcomponentsinthemixtureofresiduesfrompineandoakOriginallitterPortionofwhole(%)Percentagelostbydecompositionby:1styear2ndyear5thyear10thyearSugars1599100--Cellulose2090100--Hemicelluloses157592100-Lignins40507497100Waxes525437795Phenols510204370Wholelittermatters55.179.687.198.2StevensonFJ.CyclesofSoil.1986,pp-31TableCarbonretainedfrom14C-labeledplantmaterialappliedtofieldsoilsLocationTypeCarbonretained(%)RefereceRothmasted,EnglandRyegrasstopsandrootApproximately33%offirstyearirrespectiveofsoiltypeorplantmaterialJenkinsonWestGermanyWheatstrawandchaff31%afterfirstyearforfallowandcroppedsoilIAEAAustriaMaize47%afterfirstyearwhenappliedinAugustand33%whenappliedinOctoberIAEASaskatchewan,CanadaWheatstraw35-45%afterfirstgrowingseasonShieldsandPaulColorado,USABluegramaa.herbageb.Roots43-46%after412days63-74%after412daysNyhanNigeriaRyegrass20%afterfirstyearand14%aftertwoyears.Jenkonson&Ayanaba通氣性狀況對土壤有機質(zhì)含量的影響通氣淹水土壤黏粒含量對有機質(zhì)含量的影響水分狀況對植物體分解的影響FigDecompositionofFraxinusleavesatwetteranddriersites(Gallardo&Merino,1993)Science,1997,277:504-509PaulEA,2007SolubleinpolarsolventsNon-hydrolyzable/solubleinpolarsolventsHydrolyzableSoilorganicmatter(SOM)NotrecalcitrantCelluloseHemicellulosesProteinsRecalcitrantCutinsSuberinsHighly-recalcitrantLigninsTanninsCutansSuberansComponentsofSOM?土壤腐殖物質(zhì)腐殖物質(zhì)分組----胡敏素殘渣胡敏酸褐色沉淀富里酸黃色溶液酸化溶液----HCl土壤樣品NaOH浸提表土壤有機碳的不同組分及特性土壤有機碳組分占土壤碳比例（%）周轉時間舉例微生物量碳2-8幾個月-幾年土壤微生物量碳及微生物代謝產(chǎn)物周轉慢的碳40-5520-50年穩(wěn)定的微生物代謝產(chǎn)物，難分解的植物殘體惰性碳40-50400-2000年土壤腐殖質(zhì)LabilepoolStabilizedpoolParticulateorganicmatter(POM)MicrobialbiomassCSolubleCPotentialmineralizableCHumicsubstancesThelabilefractionconsistsofmaterialintransitionbetweenfreshplantresiduesandstabilizedorganicmatterParticulateorganicmattercanbeseparatedfromsoilsbytwodistinctmethodsresultingintwodifferentterms:lightfraction(LF)organicmatterandsand-sizedfraction(SSF)organicmatter.floatonheavyliquidsofdensitiestypicallybetween1.5and2.0g/cm3.(NaI,1.7g/cm3)LForganicmatterSSForganicmatterdefinedasorganicmatterassociatedwithsand-sizedorganicmatter(>20μmdiameterforEuropeanand>53μmdiameterforAmericanparticlesizeclassificationsystems).Itisisolatedbysievingadispersedsoil.HaynesRJ.AdvancesinAgronomy,2005MicrobialbiomassFigSchematicdiagramshowingtherelationshipbetweenvariousorganicmatterfractionsSolubleorganicmatterParticulateorganicmatterExtractableorganicmatterRootturnoverCropresiduesPotentiallymineralizableorganicmatterAdsorbedorganicmatterHumicmaterialTableTypicalquantitiesofdifferentorganicmatterfractionsinsoilsOrganicfractionTypicalquantitiesTotalorganicCandNOrganicC=7-60gC/kgParticulateorganicmatterLF=2-18%oforganicC,1-16%oftotalNSSF=20-45%oforganicC,13-40%oftotalNMicrobialbiomass1-5%oforganicCand1-6%oftotalNSolubleorganicmatterAbout0.05-0.40%oforganicCandNExtractableorganicCandNVariableamountoforganicC(1-40%)dependingontheextractantPotentiallymineralizableCandNAbout1-5%oforganicCandtotalNHaynesRJ.AdvancesinAgronomy,2005Meanresidencetime(MRT)ofsoilorganicmatterThetermmeanresidencetimehasbeenusedtoexpresstheresultsof14Cmeasurementsfortheaverageageofmodernhumus.14CdatingmethodStevensonFJ.CyclesofSoil.1986,pp-31Theformularelatingtoageto14CactivityiswhereAisthenumberofradioactivenucleiremainingaftertimeintervalt,A0isthenumberofradioactivenucleipresentatzerotime,tistimeoragesincezerotime,andt1/2isthehalf-lifeofradioactivenuclide.TableMeanresidencetime(MRT)fordifferentorganicmatterfractionsofaChernozemicblacksoilStevensonFJ.CyclesofSoil.1986,pp-31ComponentMRT,yearsUnfractionatedsoil870±50Acidextractofsoil325±60Fulvicacid495±60Humicacidtotalsample1235±60acidhydrolysate25±50nonhydrolyzable1400±60Humintotalsample1140±50acidhydrolysate465±50nonhydrolyzable1230±60RecentanalyticalandexperimentaladvanceshavedemonstratedthatmolecularstructurealonedoesnotcontrolSOMstability:infact,environmentalandbiologicalcontrolspredominate.StevensonFJ.CyclesofSoil.1986,pp-31Wearguethatthepersistenceoforganicmatterinsoilislargelyduetocomplexinteractionsbetweenorganicmatteranditsenvironment,suchastheinterdependenceofcompoundchemistry,reactivemineralsurfaces,climate,wateravailability,soilacidity,soilredoxstateandthepresenceofpotentialdegradersintheimmediatemicroenvironment.SchmidtMW,etal.2011.Persistenceofsoilorganicmatterasanecosystemproperty.NATURE,478:49-56InorganicCinsoil(SIC)Intheformofcalciumandmagnesiumcarbonates,estimatedtototalsome695to748billiontons,presentmainlyinthesoilsofsemiaridandaridareas.Thoughnotnearlyaslabileasorganiccarbon,SICcanbesolubilizedbyacidandissubjecttoleaching.Somecarbondioxidealsodissolvesingroundwater,andmaybereleasedtotheatmospherebyeffervescenceas,forexample,whengroundwaterispumpedupandusedforirrigation(DanielHill.SoilintheEnvironment,2008).塿土剖面有機碳及無機碳含量圖加入碳酸鈣及碳酸鎂對土壤培養(yǎng)過程中CO2釋放的影響（董燕婕，2010）碳酸鈣碳酸鎂CO2emissionfromsoilOrganicCpoolinsoilInorganicCpoolinsoilBioticabiotic×Sterilizer:HgCl2UsingsolidHgCl2asasterilizertosterilizetheCO2productionfrombioticprocess.Fig5aEffectofCaCO3andHgCl2additionsonCO2emissionfromsoilpH=7.4pH=7.9ForMgCO3Fig5bTheeffectofMgCO3andHgCl2additionsonsoilCO2emissionHowcanwedifferentiatethecontributionofinorganiccarbonandorganiccarbontoCO2release?Fig.1.IllustrationofthemainstoresandflowsofCinacropland,showingthreepoolsofsoilCforsimplicity,thoughrecognizingthatsoilCspansacontinuumofforms.(Janzen,2006,SBB)4.土壤碳庫的調(diào)節(jié)Soilorganiccarboncontentisafunctionofthebalancebetweentherateoforganicmatterinputtothesoil(duetonetprimaryproductivityofactivevegetation)andtherateoforganicmatterdecay.Theratesoftheseprocessesdifferinspaceandtime,aswellasintheirsensitivitiestovaryingtemperatureandmoistureregimesresultingfrommanagementandclimatechanges.Cinsoil=f(climate,topography,vegetationandorganisms,parentmaterial,ageortime)Theamountoforganicmatterinsoildependsontheinputoforganicmaterial,itsrateofdecomposition,therateatwhichexistingsoilorganicmatterismineralized,soiltexture,andclimate.HaynesRJ.AdvancesinAgronomy,2005LabileCFigAschematicdiagramoftheCcycleinagriculturalsoilsStabilizedCPlantCCO2HarvestedCLitterdecompositionDecompositionNetprimaryproductionAtmosphericCpool(760Pg)TerrestrialCpool2860PgSOC=1550PgSIC=750PgBiota=560PgFigure1.AnthropogenicactivitiesaffectingCemissionfromtheterrestrialtotheatmosphericpool.ThedirectionofthearrowindicatesthefluxofCfromonepooltoanother.Photosynthesisandplant/soilrespirationarenaturalactivities.AllothersareanthropogenicactivitiesthatcauseemissionofCO2andothergasesfromtheterrestrialecosystemtotheatmosphere.Themagnitudeofemissioncausedbyallanthropogenicactivitiesisnotknown.(Lal.NutrientCyclinginAgroecosystems70:103–116,2004.)PhotosynthesisPlantandsoilrespirationAnthropogenicactivitiesDeforestation(1.6±0.8Pg)ConversionofnaturalintoagriculturalecosystemsBiomassburningSoiltillageDrainageofwetlandSoilerosion(1.1PgCy-1)CultivationoforganicsoilGlobalterrestrialecosystemsabsorbedcarbonatarateof1–4Pg/yrduringthe1980sand1990s,offsetting10–60percentofthefossil-fuelemissions.ShilongPiao,JingyunFang,etal.2009.ThecarbonbalanceofterrestrialecosystemsinChina.Nature,458:1009-1014.潘根興.氣候變化研究進展