植物营养元素的土壤化学3-土壤中的C(上)

第二章土壤碳素循环及调控Chapter2CarboncyclesinSoilLowcarboneconomyGHGs=greenhousegasesIPCC=IntergovernmentalPanelonClimateChange

（政府间气候变化专业委员会）“哥本哈根气候会议”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.)政府间气候变化专门委员会(IPCC)第三次评估报告（2001）二十世纪全球平均气温上升0.60.2C;从1861年以来，二十世纪九十年代是最热的10年，其中，1998年是最热的一年;在过去的一千年中，二十世纪是最热的一个世纪;从1950年到1993年，陆地夜间日平均气温每10年升高约0.2C，白天升高约0.1C。海面气温升高约为陆地的一半.海平面上升；降水分布发生变化；沙漠化加剧；自然灾害发生频繁增加。全球变暖的后果?HumanpopulationSizeResourceuseHumanenterprisesAgricultureIndustryRecreationInternationalcommerceLandtransformation

LandclearingForestryGrazingIntensificationBioticadditionsandlosses

InvasionHuntingFishingGlobalbiogeochemistry

CarbonNitrogenWaterSyntheticchemicalsOtherelementsClimatechange

EnhancedgreenhouseAerosolsLandcoverLossofbiologicaldiversity

ExtinctionofspeciesandpopulationsLossofecosystems改进能源结构提高能源效率植树种草，增加生态系统对CO2的吸收如何减少温室效应气体的排放?Csequestration(碳固定)CarbonsequestrationimpliesthenetremovalofCO2fromtheatmosphereintolong-livedpoolsofC,suchasterrestrialandgeologic.Inotherwords,itiscapturingandsecurelystoringCbybioticphotosynthesisandabioticinjectionintogeologicstrataoroceanprocesses.LalR.SoilSci.Soc.Am.J.2007,71:1425–1437Carbonsequestration1997年12月，面对环境恶化，气候变暖，在日本京都举行的联合国气候大会通过了《京都议定书》，目标是在2008年至2012年间，将发达国家CO2等６种温室气体的排放量在1990年的基础上平均削减5.2％。为了使议定书真正发挥作用，协议规定，只有在占1990年全球温室气体排放量55％以上的至少55个国家批准后才能生效。京都议定书（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)我国2001年的工业CO2排放为1Pg/yr，仅次于美国（1.84Pg/yr），预计在2005年会超过美国,达到2Pg/yr，我国面临着减排的巨大压力。这是一个关系国家环境外交和农业可持续发展的食物安全与环境安全保障的重大问题。黄耀.第四纪研究.2006按照IPCC第2次评估报告提供的全球增温潜势数据计算,1994年中国温室气体总排放量为36.50×108tCO2当量,其中CO2,CH4和N2O分别占73.1%,19.7%和7.2%。能源活动是中国CO2排放的主要来源,占90.95%；农业活动和能源活动是CH4排放的主要来源，分别占50.15%和27.33%；农业活动是N2O排放的主要来源,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全球气候变化简史不同的声音.“气候变化问题的非主流思考：事实与逻辑”,科学时报,2009年8月11“哥本哈根闹剧后的沉思”,科学时报,2010-02-11气候问题的“邮件门”

(2009年11月)英国东英吉利大学气候研究中心上千封电子邮件和3000多份有关气候变化的文件被曝光，这些文件显示：这些气象学家利用各国政府对气候变化问题的关心，用一些不实数据制造气候变暖的假象，营造恐慌心理，然后从政府或其他机构手中骗得了更多的科研经费。气候问题的“冰川门”事件IPCC在2007年发布的第四次评估报告中写道“喜马拉雅冰川的消融速度超过了世界其他地区的冰川，如果全球变暖的速度持续下去，喜马拉雅冰川在2035年甚至更早前消失的可能性非常高”。客观对待IPCC的报告美国250余名科学家联名上书呼吁不要指责IPCC荷兰250余名科学家联名问题与对策:我国已成为全球最大的温室效应气体排放国，面临着减排的巨大压力。丁仲礼,段晓男,葛全胜,张志强.2050年大气CO2浓度控制:各国排放权计算.中国科学，D辑，2009，39(8):1009-1027文章提出了“人均累计排放指标”的概念，以体现“共同而有区别的责任”原则和公平正义准则。设定2050年前将大气CO2浓度控制在470ppmv的目标,以1900年为时间起点,对各国过去(1900-2005年)人均累计排放量、应得排放配额以及今后(2006-2050年)的排放配额做了逐年计算.全球碳循环概况土壤碳库在全球碳循环中的作用土壤碳的不同组分及其特性土壤碳库的调节TableDistributionofCinsomeofthemaincompartmentsintheearth(Delwiche)CompartmentAmountofC,×1012kgAtmosphere700Soilorganicmatter(to2mdepth)2500Landlifeforms480Marinehumus3000Oceanlifeforms50Dissolvedcarbonate-bicarbonateinoceans3840Coalandpetroleum1×104

Sediments6×107

StevensonFJ,1986(1)全球碳分布全球碳循环概况FigThecarboncycle(Numbersarestorageas1015gorfluxesas1015gperyear)Ecology,ManuelCM,2002为了维持全球碳平衡，其焦点不是各个库的碳贮存总量，而是每年碳的去处和动态变化问题。“源”与“汇”

(sourceandsink)把释放二氧化碳的库称为“源”，吸收二氧化碳的库称为“汇”。PaulEA,2007(2)全球碳循环

SoilOceanBiotaAtmosphereTerrestrialphotosynthesisRivertransportoforganicmatterandcarbonatesRespirationCarbonateinputCO2exchangeLitterandrootinputCalcificationMarinerespirationMarinephotosynthesisTheshort-termCcycle人为因素对碳循环的干扰作用(单位Pg/年）大气土地海洋沉积物矿质有机碳碳酸盐地质库5.4矿质燃料燃烧5.3水泥生产0.1土地利用变化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.土壤碳库在全球碳转化及循环中的地位LalR.Science,2004Theglobalsoilcarbon(C)poolof2500gigatons(Gt)includesabout1550Gtofsoilorganiccarbon(SOC)and950Gtofsoilinorganiccarbon(SIC).ThesoilCpoolis3.3timesthesizeoftheatmosphericpool(760Gt)and4.5timesthesizeofthebioticpool(560Gt).(1)土壤碳库的意义AtmosphericCpool(760Pg)TerrestrialCpool2860PgSOC=1550Pg(to1mdepth)SIC=750PgBiota=560PgFigure1.Cycleof

Cin

terrestrialecosystemandtheatmosphere.PhotosynthesisPlantandsoilrespirationLalR.Science.2004,304土壤碳库的稳定、增长或释放与大气库的变化有重要的关系，土壤能否增加碳储存是关乎陆地生态系统净碳汇饱和问题的重要理论基础，这一问题已成为土壤与全球变化研究的重点和热点科学问题。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)土壤碳贮量(Cstorage)土壤碳贮量的计算？土壤碳贮量=土壤容重×土壤有机碳含量×土壤体积Soilorganiccarbon=1550PgSoilinorganiccarbon=750PgYu,D.,etal.,RegionalpatternsofsoilorganiccarbonstocksinChina.JournalofEnvironmentalManagement(2006),Yu,D.,etal.,RegionalpatternsofsoilorganiccarbonstocksinChina.JournalofEnvironmentalManagement(2006),SoilsinChinacoveranareaof9.281×106km2intotal,withatotalSOCstockof89.14Pg(1Pg=1015g)andameanSOCdensityof96.0tC/ha.中国是世界上平均土壤碳密度较低的国家。全球全土碳密度平均为121t/hm2，我国全土平均有机碳密度的报道值介于80～105t/hm2，均远远低于世界平均值。表中国和欧洲表层土壤有机碳密度比较(tC/ha)土地利用欧洲中国土地总计70.852.0耕地53.037.0潘根兴，赵其国.地球科学进展.2005不同土地利用方式对土壤剖面碳贮量的影响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植物体组成及分解转化特性土壤有机碳的组分及特性土壤有机碳稳定性的机理3.土壤碳的不同组分及其特性PlantlitterastheprinciplesourceofsoilorganicmatterformationPlantsarethemainsourceofcarbontosoilsthroughtissueresiduesorviarootexudatesandsymbioticfungi.陈兴丽等表1黄土高原几种植物残体的化学成分植物残体有机碳CTOC(g·kg-1)全氮NTotalN(g·kg-1)C/NRatios木质素(%)乔木A榆树422.5825.3616.6625.20B小叶杨414.449.0245.9730.89C刺槐437.7314.9229.3327.78灌木D柠条466.8530.9515.0829.59E沙棘464.7029.7115.6427.14F山桃458.5328.2916.2125.76草本G长芒草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+能量在通气不良的情况下，可形成中间产物有机酸（丁酸）和甲烷、氢气C6H12O6CH3CH2CH2COOH+2H2+2CO2+能量4H2+CO2CH4+2H2O碳水化合物的矿化有机物质的矿化腐殖物质形成的生物学示意图

植物残体

在微生物作用下转化

糖

多酚

氨基化合物

木质素分解产物

类木质素

醌

醌

腐殖物质

1234Firststage:StevensonFJ,1986StagesinthemicrobialdecompositionDecayofeasilydegradablesubstances.PartialconversiontoCO2andbodytissueSecondstage:Thirdstage:Fourthandsuccessivestage:Celluloseandothercarbohydratesutilizedwithfurtherweightreduction.Formationofnewbodytissue.Partofpreviousbiomassmineralized.Furtherdecreaseincellulose.Initiationoflignindecomposition.Furtherdecreaseinbiomass.Furthercycling.Forplantresidues,aboutone-thirdofthecarbonwillremaininthesoilattheendofthegrowingseason.陈兴丽等图1黄土高原不同植物残体碳的矿化率C/NA榆树16.66B小叶杨45.97C刺槐29.33D柠条15.08E沙棘15.64F山桃16.21G长芒草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)图1土壤植物生态系统中的碳、氮素转化过程示意图不同C/N比的植物残体等土壤微生物量部分稳定的有机氮

稳定的腐殖质态氮NH3,NO3-NH3,NO3-腐殖化作用施用肥料作物吸收CO2等释放土壤中氮、碳协调是关键！有机物施入土壤的去向（1年后）：有机残体（100）CO2（60-80%）土壤生物体（3-8%）非腐殖物质（多糖、有机酸等）（3-8%）腐殖物质（10-30%）腐殖质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通气性状况对土壤有机质含量的影响通气淹水土壤黏粒含量对有机质含量的影响水分状况对植物体分解的影响FigDecompositionofFraxinusleavesatwetteranddriersites(Gallardo&Merino,1993)Science,1997,277:504-509PaulEA,2007SolubleinpolarsolventsNon-hydrolyzable/solubleinpolarsolventsHydrolyzableSoilorganicmatter(SOM)NotrecalcitrantCelluloseHemicellulosesProteinsRecalcitrantCutinsSuberinsHighly-recalcitrantLigninsTanninsCutansSuberansComponentsofSOM?土壤腐殖物质腐殖物质分组----胡敏素残渣胡敏酸褐色沉淀富里酸黄色溶液酸化溶液----HCl土壤样品NaOH浸提表土壤有机碳的不同组分及特性土壤有机碳组分占土壤碳比例（%）周转时间举例微生物量碳2-8几个月-几年土壤微生物量碳及微生物代谢产物周转慢的碳40-5520-50年稳定的微生物代谢产物，难分解的植物残体惰性碳40-50400-2000年土壤腐殖质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).塿土剖面有机碳及无机碳含量图加入碳酸钙及碳酸镁对土壤培养过程中CO2释放的影响（董燕婕，2010）碳酸钙碳酸镁CO2emissionfromsoilOrganicCpoolinsoilInorganicCpoolinsoilBioticabiotic×Sterilizer:HgCl2UsingsolidHgCl2asasterilizertosterilizetheCO2productionfrombioticprocess.Fig5aEffectofCaCO3andHgCl2additionsonCO2emissionfromsoilpH=7.4pH=7.9ForMgCO3Fig5bTheeffectofMgCO3andHgCl2additionsonsoilCO2emissionHowcanwedifferentiatethecontributionofinorganiccarbonandorganiccarbontoCO2release?Fig.1.IllustrationofthemainstoresandflowsofCinacropland,showingthreepoolsofsoilCforsimplicity,thoughrecognizingthatsoilCspansacontinuumofforms.(Janzen,2006,SBB)4.土壤碳库的调节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.潘根兴.气候变化研究进展