读书报告4土壤碳固定对全球气候变化和粮食安全的影响

SoilCarbonSequestrationImpactsonGlobalClimateChangeandFoodSecurityTutor:Prof.ZHENGSpeaker:DongXiaogangDate:2012-05-10R.Lal,etal.2004Science304,1623土壤碳固定对全球气候变化和粮食安全的影响2.SoilCarbonSequestration3.SoilCarbonSequestrationforMitigatingClimateChange4.SoilCarbonSequestrationandGlobalFoodSecurity5.Conclusions1.BackgroundContentTheglobalsoilcarbon(C)poolof2500gigatons(Gt)includesabout1550Gtofsoilorganiccarbon(SOC)and950Gtofsoilinorganiccarbon(SIC).1.BackgroundThesoilCpoolis3.3timesthesizeoftheatmosphericpool(760Gt)and4.5timesthesizeofthebioticpool(560Gt,fig.S1).25000亿吨的全球土壤碳库由15500亿吨的土壤有机碳和9500亿吨的土壤无机碳组成。土壤碳库的容量是大气碳库的3.3倍，是生物碳库的4.5倍。Fig.1.Processesaffectingsoilorganiccarbon(SOC)dynamics.TheSOCpoolrepresentsadynamicequilibriumofgainsandlosses(Fig.1).土壤碳库处于收支动态平衡。SeveredepletionoftheSOCpooldegradessoilquality,reducesbiomassproductivity,andadverselyimpactswaterquality,andthedepletionmaybeexacerbatedbyprojectedglobalwarming.ThedepletionisexacerbatedwhentheoutputofCexceedstheinputandwhensoildegradationissevere.当输出超过输入和土壤退化严重时土壤碳库的耗竭将加剧。土壤碳库的严重耗竭使得土壤质量退化，生物产量降低，影响水质量，预测的全球变暖可能会加剧土壤碳库的耗竭。TheestimatesofhistoricSOClossrangewidely,from44to537Gt,withacommonrangeof55to78Gt(3).以往的土壤有机碳的损失量的估算值变化范围广大约从440到5370亿吨，而共识的损失量是550到780亿吨。2.SoilCarbonSequestrationCarbonsequestrationimpliestransferringatmosphericCO2intolong-livedpoolsandstoringitsecurelysoitisnotimmediatelyreemitted.Thus,soilCsequestrationmeansincreasingSOCandSICstocksthroughjudiciouslanduseandrecommendedmanagementpractices(RMPs).土壤碳固定意味着将大气中的CO2转移到长期存在的土壤库中并安全地储存它，因此使碳不能立即释放到大气中。因此土壤碳固定意味着通过精确的土地使用和推荐的管理措施(RMPs)增加了土壤有机和无机碳库的容量。TheSOCsequestrationiscausedbythosemanagementsystemsthataddhighamountsofbiomasstothesoil,causeminimalsoildisturbance,conservesoilandwater,improvesoilstructure,enhanceactivityandspeciesdiversityofsoilfauna,andstrengthenmechanismsofelementalcycling(Fig.2,tableS2).土壤有机碳的固定是由向土壤中增加高生物量，使土壤受到最小的扰动，保持水土，提高土壤结构，增强土壤动物的种类和多样性的活性，增强元素循环而实现的。(Fig.2,tableS2)2.SoilCarbonSequestrationFig.2.具有高的土壤碳固定潜能的态系统有:农田，放牧的草地，退化的或沙漠化土地,灌溉的土壤放牧的草地的生态系统的土壤碳固定潜力不包括在全球的土壤碳固定中，这是因为它部分的被覆盖在其它生态系统下以及具有很大的不确定性。CommonRMPsthatleadtoSOCsequestrationaremulchfarming,conservationtillage,agroforestryanddiversecroppingsystems,covercrops(Fig.3),andintegratednutrientmanagement,includingtheuseofmanure,compost,biosolids,improvedgrazing,andforestmanagement.通常导致土壤有机碳固定的RMPs措施是：覆盖农业，保护性耕作，混农林和多样性种植系统(Fig.3)，和包括由粪肥、堆肥、生物固体、改善的放牧模式和林地管理的使用的综合养分管理。2.SoilCarbonSequestrationFig.3.Importantrecommendedmanagementpracticesareno-tillfarming,covercrops,manuringandagroforestry.(A:Long-termno-tillplotsB:Agroforestry)TherateofSICsequestrationassecondarycarbonatesislow(5to150kgC/haperyear)andisaccentuatedbybiogenicprocessesandleachingofcarbonatesintothegroundwater(11,12),especiallyinsoilsirrigatedwithwatercontaininglowcarbonates.作为处于次要地位的碳酸盐，土壤无机碳的固定的速率是很低的(每年5到150kgC/ha)，土壤无机碳作为生命必须的过程和碳酸盐向地下水的淋洗过程被重视，(11,12)特别是在含有低碳酸盐的水中的土壤灌溉区。2.SoilCarbonSequestration•土壤无机碳的固定3.SoilCarbonSequestrationforMitigatingClimateChange土壤碳固定对气候变化的缓解EstimatesofthetotalpotentialofCsequestrationinworldsoilsvarywidelyfromalowof0.4to0.6GtC/year(9)toahighof0.6to1.2GtC/year(13).Thus,thepotentialisfiniteincapacityandtime.Nonetheless,soilCsequestrationbuysustimeuntilthealternativestofossilfueltakeeffect.Someissuesrelatedtothisstrategyareasfollows:全球土壤碳固定总的潜力的估算值是非常广泛的，从低的0.4to0.6GtC/year(9)到高的0.6to1.2GtC/year(13)。因此，这种固定的潜力在容量和时间上是有限的。尽管如此，直到我们能找到化石燃料的替代品时，土壤碳固定为我们争取了时间。(1).Agriculturalchemicals农化用品MostRMPsinvolveC-basedinput.Item(1Kg)NeedC(Kg)N0.86P2O50.17K2O0.12Lime0.36Herbicides4.7Fungicides5.2Insecticides4.9However,inputsareneedednotforsoilCsequestrationperse,butforincreasingfoodproductionandensuringsustainableuseofsoilandwaterresources.(1).Agriculturalchemicals然而输入不仅是为了土壤碳固定自身，也是增加了粮食生产，确保水土资源使用的可持续。(2).Nutrientsrequired养分需求Itisestimatedthatsequestrationof1GtofCinworldsoilswouldrequire80milliontons(Mt)ofN,20MtofP,and15MtofK.Incomparison,theglobalfertilizerusein2000was136Mt(17).据计算，世界土壤中10亿吨的碳固定需要8000万吨的N，2000万吨的P，1500万吨的K。与此相比，2000年全球肥料的施用量为1.36亿吨（17）。Onetonofcerealresiduecontains12to20kgN,1to4kgP,7to30kgK,4to8kgCa,and2to4kgMg.Annually,3Gtofresiduesofgraincropsareproducedglobally(tableS3),whichifrecycledratherthanremovedforfuelandotheruses,wouldimprovesoilqualityandsequesterC.一吨的禾谷类作物残渣含有12到20Kg的N，1到4Kg的P，7到30Kg的K,4到8Kg的Ca以及2到4Kg的Mg。每年全球有30亿吨的禾谷类作物残渣被生产(tableS3)，这些作物残渣如果是循环利用而不是用于燃料和其它方面的使用，将提高土壤质量和固定碳。(2).NutrientsrequiredCropresidueisalsoapotentialsourceofenergybydirectcombustion,orforproductionofethanolorH2.ItcanbeusedeitherforbiofuelproductionortosequesterCandimprovesoilquality.Theeconomicsofthesetwocompetingusesneedtobeassessed.作物残渣通过直接的燃烧也是能源的一个潜在的库，或者也可以作为乙醇或氢气的生产原料。作物残渣既可以用于生物燃料的生产或用于碳的固定以提高土壤质量。这二者的竞争使用的经济效益需要被评估。(3).Soilerosionanddeposition土壤的侵蚀和沉积TheSOCispreferentiallyremovedbywind-andwater-bornesedimentsthrougherosionalprocesses.SomeoftheSOC-enrichedsedimentsareredistributedoverthelandscape,othersaredepositedindepressionalsites,andsomearecarriedintotheaquaticecosystems(Fig.1).Yet,aneffectivesoilerosioncontrolisessentialtosusta