全球碳循環(huán)_Photosynthesis and Respiration_lecture3（英文）

1、Lecture 3&4: Terrestrial Carbon ProcessI. Photosynthesis and respiration (revisit)II. Carbon Stocks and Fluxes in Terrestrial EcosystemsIII. Terrestrial Ecosystems A. Ecosystem Concept B. Ecosystem Carbon Balance (GPP, NPP, NEP, NBP) VI. Missing carbon sinks? Lecture 3: Photosynthesis and Respiratio

2、n1. What is the Photosynthesis?2. Where the Photosynthesis Occurs?3. How Photosynthesis works? Key Processes 4. Alternative Photosynthesis PathwayPhotosynthesis Overview1. What is the Photosynthesis?Photosynthesis is the biogeochemical process by which Plants cover atmospheric CO2 to carbon producti

3、ons that results in plant growth is the conversion of light-energyto chemical-energy via the chloroplasts generates 170 billion metric tonsof sugar annually, which enters our biosphere We express this combined knowledge as the photosynthetic equation:6CO2 + 12H2O + light energy - C6H12O6 + 6O2 + 6H2

4、O(or CO2 + 2H2O + light energy - CH2O+ O2 + H2O)Photosynthesis takes place within leaf (or green stem) cells containing chloroplastse.g. each cell contains 40 to 50 chloroplasts a chloroplast has dozens of the thylakoids and millions of pigment molecules each thylakoid contains thousands of photosys

5、tems2. Where the Photosynthesis Occurs?Photosynthetic Overview A. There are three basic steps in photosynthesis: (1) Light Reactions - energy capture (2) Dark Reactions - fixation of carbon (3)Pigment Regeneration electron replacement from the splitting of H2O in oxygenic photosynthesis.3. How Photo

6、synthesis works? key processes C3 photosynthesis ( three-carbon sugars) C3 plant(2) Crassulacean Acid Metabolism (CAM) (1) C4 Photosynthesis 4. Alternative Photosynthetic PathwaysSome plants (e.g., corn,sugarcane, and many tropical grass)begin the photosynthetic process by producing a four-carbon co

7、mpounds. Plants of this type are called C4 plants(e.g. live in hot and dry environments and are able to photosynthesizeat low CO2 concentration) Like C4 plant, CAM is an adaptation to hot dry environmentsCAM plats utilize both the C3 and the C4 pathways of photosynthesisCO2 is fixed by PEP (phosphho

8、enolpyruvate) carboxylase at night to form malic acid which is then is stored in the vacuole of the cell.Respiration Overview1. Autotrophic Respiration (Plant Respiration) A. Maintenance Respiration B. Growth Respiration 2. Heterotrophic Respiration (Soil Respiration) 1.Autotrophic Respiration (Ra)R

9、a involves the oxidation of organic substances to CO2 and water: CH2O+ O2 - CO2 + 2H2O +energy Total autotrophic respiration (Ra) consists of two major components:(1) Maintenance Respiration (Rm)(2) Growth Respiration (Rs)Maintenance Respiration: the basal rate of metabolism, includes the energy exp

10、ended on ion uptake and transfer within plants. (a) The temperature is most important environmental factor affecting maintenance respiration Protein synthesis rates increase exponentially with increasing temperature (T)(b) The T dependence of Rm is expressed in term of the Q10, or change in rate wit

11、h a 10C rise in temperature:Rm (T) = R0 Q10 (T-T0)/10 Where: R0 is the basal respiration rate at T= 0C (or ref. T)Q10 represents the change in the rate of respiration for 10C change in T (about 2.0-2.3) (c) using plant nitrogen contentMicheal Ryan (1991) derived an empirical relationship based on a

12、wide variety of species and plant tissues:Rm = 0.0106 NWhere Rm is maintenance respiration (moles C per hour), and N is plant nitrogen in moles of N. (see Ryan 1991, Ecological Applications, 1: 157-167).Most of the organic N in plants is in protein and about 60% Rm supports protein repair and replac

13、ement (2) Growth Respiration (Construction respiration)(a) Rg includes the carbon cost of synthesizing new tissue from glucose and minerals. (b) Rg for various tissues differ, depending on the biochemical pathways involved.e.g.: 1 g lignin requires 2.5g of glucose 1 g needles require 1.28 g of gluco

14、se 1 g roots require 1.2 g of glucose (C) Growth respiration can be estimated based on construction cost Estimating Growth respiration (Rg)Growth respiration is generally considered to be independent of temperature and is proportional to GPP:Where rg,i is a growth respiration coefficient for plant c

15、omponent i, and ra,i is the carbon allocation fraction for plant component i. Ryan (1991) used 25% for overall and root growth respiration coefficient. In the TEM (Mellilo et al. 1993), 20% of GPP is applied to growth respiration. 2. Heterotrophic Respiration (Rh) 1) ConceptThe form of respiration b

16、y which organic matter is converted back into CO2, mainly by soil micro-organisms. 2) Modeling RhSoil respiration (total soil CO2 flux) including:root respiration and decomposition litter decompositionsoil organic matter decompositionLinear/nonlinear modelsMoisture and temperature combined modelsLin

17、ear/nonlinear modelPeng and Apps (2000) used the 150 sites published by Raich and Schlesinger (1992)to develop TPAET models for estimating soil respiration (SR) at global scaleGroup A: Major Natural Ecosystems (n=117)SR = 7.6 exp (0.029T) P0.171 AET0.423 (R2 = 0.70)Group B: Croplands (n=19)SR = 0.66

18、P + 0.95 AET 7.11T 468 (R2 = 0.71)Group C: Wetlands (e.g. bogs, mires, and marshes) (n=14)SR = 0.722 AET 0.023P-10.241T140 (R2 = 0.74)Where T is mean annual temperature; P is annual precipitation;AET is actual evapotranspiration(Ref. Peng, C.H. and M.J. Apps 2000. J. of Environmental Sciences, 12: 257-265)Moisture and temperature combined modelsIn CENTURY (Parton et al, 1993), the rate of soil C decomposition for each pool (Ri) is e