全球碳循环-Terrestrial-Carbon-Process-lecture4(英文).ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Lecture 4:Terrestrial Carbon Process,I.Carbon Stocks and Fluxes in Terrestrial Ecosystems,II.Terrestrial Ecosystems,A.Ecosystem Concept,B.Ecosystem Carbon Balance(GPP,NPP,NEP,NBP),III.Missing Carbon sinks,Fluxes and Pools of,Carbon,on the Earth,Carbon pool:,The reservoir containing carbon,(carbon stock),Carbon flux:,The rate of exchange of carbon between,pools(i.e.reservoirs),Carbon sinks:,Carbon reservoirs and conditions that,take-in and store more carbon(e.g.carbon,sequestration)than they release.,Carbon sources:,Carbon reservoirs and conditions that,release more carbon than take-in and store,Carbon sequestration:,The uptake and storage of carbon,Terminology,Pg C:,petagrams of carbon(1 Pg C=10,15,g C=1 billion tons C),Gt C:,gitatonnes of carbon(1 Gt C=1 Pg C),Mt C:,megatonnes of carbon (1 Mt C=10,12,g C),Tg C:,teragrams of carbon(1 Tg C=1 Mt C),(1 Pg C=3.7 Pg carbon dioxide),2).The Units of Carbon,1 C=3.7 CO,2,1.Terrestrial ecosystems are important components in,the global carbon cycle that create many of the sources and sinks,of CO,2,(methane,and nitrous oxide);,The Ecosystem Concept,The ecosystem including“not only the organism-complex,but the whole,complex of physical factors forming what we call the environment”,(,Tansley,1935),Whittaker(1975)suggested that“an ecosystem is a functional system that includes assemblage of interacting organisms(plants,animals and microbes)and their environment,which acts on them and on which they act.”,Ecosystem:,Biotic community:,Plant,animal,microbial community,Abiotic environment:,atmosphere,soil and geological substrate,2.The dynamics of terrestrial ecosystem depend on interactions,between a variety of biogeochemical cycles,particularly the carbon cycle,the cycles of nutrient and water.,For example:the interconnectedness of the various living and,nonliving components of ecosystem that a change in any one,will results in a subsequent change in almost all others.,3.Carbon Balance of Terrestrial Ecosystem(4 important concepts),GPP(Gross Primary Production):,The total amount of carbon fixed in the process of photosynthesis,by plants in an ecosystem,such a stand of trees.,Global total GPP:,120,Gt,C yr,-1,(b),NPP(Net Primary Production):,The net production of organic matter by plants in an ecosystem,that is,GPP reduced by losses resulting from the respiration,of plants(autotrophic respiration,R,a,).,NPP=GPP-R,a,Global total NPP:60 Gt C yr,-1,(c)NEP(Net Ecosystem Production):,The net accumulation of organic matter or carbon by an ecosystem.,NEP=NPP-R,h,(heterotrophic,respiration),R,h,includes losses by herbivory and the decomposition of organic,debris by soil biota(=50 Gt C yr,-1,),Global total NEP:10,Gt C yr,-1,(NEP is also called,NEE-net ecosystem exchange,),(d)NBP(Net Biome Production):,The net production of organic matter in a region containing,a range of ecosystem(a biome).,NBP=NEP non-respiratory C losses,through ecosystem disturbances,(harvest,forest fire,clearance,insect etc.),(by Schulze,E-D and M.Heimann,1998),Global NBP:is small(about,1 Pg C for 1989-1998),NEP and NBP are key indicators used to describe,the annual net C balance of forest ecosystems,CO,2,Med.-term,Carbon,Storage,GPP,=120 Gt C yr,-1,NPP,60 Gt C yr,-1,NEP,10 Gt C yr,-1,NBP,1 Gt C yr,-1,Short-term,Carbon,Uptake,Long-term,Carbon,Storage,Plant Respiration,(60Gt C yr-1),Decomposition,(50Gt C yr-1),Disturbance,(9 Gt C yr-1),50%,5%,0.5%,CO,2,assimilation,4.Carbon Stocks and Flows in Major Biomes of Terrestrial Ecosystems,-Total ecosystem area:151.2,10,6,km,2,-Vegetation carbon:,500 Gt C,-Soil carbon:,2000 Gt C,-Total terrestrial biomes:,2500 Gt C,Forests contain a large part of carbon stored on land,in the form of biomass(trucks,branches,foliage,roots etc.)and,in the form of soil organic carbon.,Grassland ecosystems store most of their carbon in soils,where turnover is relatively slow.,Wetlands are important carbon reservoirs.,-Undrained peatlands in high latitude -C sinks,(0.2-0.5 t C ha,-1,yr,-1,),but,sources of methane,(0.03-0.3 t CH4 ha,-1,yr,-1,);,-,Peatlands,that are drained for agriculture,or for,afforestation,release carbon as CO,2,No significant methane release.,In croplands,carbon stocks are primarily in the form of,below-ground plant organic matter and soil,Atmospheric evidence of large carbon exchanges,by the biosphere,3).Major carbon pools on the Earth,The Earth contains about 10,23,g of carbon,Active surface Pools,Atmosphere:7.5,x 10,17,g(=750 Pg),Land plants:6.1 x 10,17,g (=610 Pg),Soils:1.6 x 10,18,g (=1,600 Pg),Ocean Dissolved Inorganic carbon:3.9 x 10,19,g,(surface and deep oceans)(=39,000 Pg),Fossil Fuels and cement production:4 x 10,18(,=4,000 Pg),-,Sedimentary rocks,organic compounds:1.56,x 10,22,g,carbonate:6.5 x 10,22,g,4).Major carbon fluxes on the Earth,NPP(net primary production)on land:60 Pg yr.,-1,-Photosynthetic Uptake 120 Pg yr.,-1,-Plant Respiratory Loss-60 Pg yr.,-1,Soil Respiration-60 Pg yr.,-1,Fossil Fuels 5.5 Pg yr.,-1,Land Use Changes 1.6 Pg yr.,-1,Ocean Uptake(physiochemical diffusion)92 Pg yr.,-1,Ocean Release(physiochemical diffusion)90 Pg yr.,-1,Two important factors contributing,global carbon budgets,Contemporary carbon cycle is controlled primarily by,the rate,at that carbon moves in and out of these pools,not by their size;,Small change in the rate of large carbon pools can have,a dramatic impact on the atmospheric CO,2,For example:,Calcium carbonate in desert soil:930 Pg C(930 x10,15,g C),Flux from this pool to atmosphere:0.0023 Pg C yr,1,(85,000 years turnover time!),For example:,A 0.1%increase in the rate of decomposition on land,release about 0.6 Pg C/yr to the atmosphere,2.The Missing Carbon Sinks,Atmospheric Imbalance-the Missing Carbon Sink?,Net sources of CO,2,to the atmosphere(in units of 10,15,g),Fossil Fuels-5.5 Pg yr.,-1,Land Use Change-1.6 Pg yr.,-1,Net sinks for CO,2,from the atmosphere,Atmospheric Increase 3.2 Pg yr.,-1,Oceanic uptake(increase)2.0 Pg yr.,-1,Net carbon emissions=Net carbon sinks,Imbalance 1.9 Pg yr.,-1,(unknown carbon sinks),(ref.1980 to 1989),Missing Carbon Sinks:,The imbalance between carbon emissions and sinks,(of about 1.9 Pg C yr,-1,for 1980s)is often refereed to,as the“missing carbon sinks”,Hypothesis 1:,There is a large terrestrial sinks for anthropogenic CO,2,in the Northern Hemisphere,Hypothesis 2:,The ocean carbon sinks will continue to increase in response,to rising atmospheric concentrations,But,the rate of increase,will be modulated by changes in ocean circulation,biology,and chemistry,Finding the Missing Carbon Sinks,Take home message:,Two Questions,1.What are the evidences in support of the terrestrial,carbon sinks?,2.What are the major factors contributing the terrestrial,carbon sinks?,A.Expected CO,2,North-South Gradient:,The smaller than expected north-south gradient of atmospheric CO,2,combine,With data on the partial pressure of CO,2,in ocean surface waters,suggests that,There is a large terrestrial carbon sinks at temperate latitudes in the,Northern Hemisphere(Tans et al.,1990),Tans,P.,I.Y.Fung,and T.Takahashi.1990.Observational constraints on the global atmospheric CO2 budget.,Science,247:4131-1438.,1.What are the evidences in support of the terrestrial carbon sinks?,B.Isotopic Fractionation:,The existence of a large terrestrial sink,at northern latitude is supported by,13,C/,12,C ratio measurement,in atmospheric CO,2,(Ciais et al.,1995)and by measurements of,the O,2,/N,2,ratio(Keeling et al.,1996).,Ciais,P.,P.P.Tans,M.Trolier,J.W.C.White,and R.J.Francey.1995.A large north hemisphere,terrestrial CO2 sinks indicated by the,13,C/,12,C ration of atmospheric CO2.Science:269:1098-1102,.,Keeling,R.F.,S.C.Piper,and M.Heimann.1996.Global and hemisphere CO2 sinks deduced from,changes in atmospheric O2 concentration.,Nature,381:218-221.,C.New Technique of Eddy Covariance:,Flux measurements obtained by,this technique in different ecosystems have demonstrated the ability,of some forest to act as significant net sinks for atmospheric CO,2,(Wofsy et al.,1993),Wofsy,S.C et al.1993.Net exchange of CO2 in a mid-latitude forest.,Science,260:1314-1317.,D.Recent Forest Inventory:,suggested that there has been a substantial,increase in the carbon stock in northern forest biomass,of the order of,06-0.8 Pg C y,-1,(Caspersen et al.,2000;Fang et al.2001Goodale et al.2002),Caspersen,J.P.,et al.2000:Contributions of land-use history to carbon accumulation in U.S.forests.,Science,290,1148-1151.7,Fang,J.A.Chen,C.Peng,X.Zhao,and L.Ci,2001:Changes in forest biomass carbon storage in,China between 1949 and 1998.,Science,292,2320-2322.,Goodale,C.L.et al2002.Forest carbon sinks in the Northern Hemisphere.,Ecological.Application,12:891-899,E.Remote Sensing Estimates:,A,large carbon sink,of order 0.68 Pg C,Was found in the woody biomass of Northern forests based on 19 years of data,from remote-sensing spacecraft and forest inventory.,Myneni,R.B.et al.2001.A large carbon sink in the woody biomass of Northern forests.,PNAS:98:14784-14789,2.What are the major factors contributing the terrestrial carbon sinks?,Several factors contribute to carbon sinks including:,Direct human impact(e.g.reforestation and tree regrowth),Indirect human impacts(e.g.CO,2,and nitrogen fertilization),Natural factors(e.g.climate variability,Fire),Schimel et al.(1995)attributed the missing carbon sinks to:,Enhance forest growth due to CO,2,fertilization(Beta factor),e.g.CO,2,stimulation of plant growth(32-41%),(2)Forest regrowth due to land-use and land cover change,(3)Increase N deposition,(4)Positive response to climate anomalies(climate variability),Ref.G.C.Hurtt et al.,Proc.Natl.Acad.Sci.USA,99,1389(2002).,Land Cover Change,in USA,