03_13_Xin - Xin Xi March 13, 2008 Basis 1. Photosynthesis...

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    Xin Xi March 13, 2008
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    Basis 1. Photosynthesis (gross photosynthesis minus photorespiration) C3/C4/ CAM (Crassulacean Acid Metabolism) 2. Ecosystem Respiration Autotrophic (Plant) Respiration Heterotrophic (Soil) Respiration 3. Terrestrial carbon budget concepts Gross Primary Production (GPP) Net Primary Production (NPP) Net Ecosystem Production/Exchange (NEP/NEE) Net Biome Production/Exchange (NBP/NBE)
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    Rubisco Rubisco Solar visible radiation temporary chemical energy (ATP+NADPH) permanent chemical energy (sugar)
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    Acronyms Mes: mesophyll cell; BS: bundle sheath cell; Rmi: mitochondrial respiration; C3 Ps: C3 carbon fixation (CO2+RuBP 2C3); C4 Ps: C4 carbon fixation (CO2+PEP C4 acid);
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    C4 vs. C3: (1). C4 acid is moved to bundle sheath cells and releases CO2 around Rubisco, thus increasing the CO2 concentration and fixation rate; Photorespiration is low; high efficiency of Rubisco reduces the demand for Nitrogen, and makes the plants survive in warm-dry environment. (2). PEP captures CO2 and increases the CO2 concentration gradient between external air and inside leaf, thus enhancing CO2 absorption with smaller stomata and less water loss. (3). For each CO2 fixation, 2 ATPs are needed to generate one PEP, causing a 30% increase in energy requirement. C4 vs. CAM: (1). CAM fix CO2 in C4 acid at night and release it at daytime for the normal C3 photosynthesis pathway. So it can close the stomata at daytime avoiding water loss in very dry environment (e.g, pineapple). (2). CAM has a temporal separation of C3 and C4 fixation, while C4 has a spatial separation of C3 and C4 fixation between bundle sheath and mesophyll cells. NOTE: plants can adapt to the environment and change their photosynthesis paths.
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    2. Respiration Ecosystem Res. (Reco) = Autotrophic Res. (Ra) + Heterotrophic Res. (Rh) Autotrophic (Plant) Respiration : carbon lost by plant itself (biomass above and below ground) CH2O + O2 CO2 + H2O + energy Maintenance respiration : basal rate of plant metabolism; Temperature Growth respiration : use carbon to synthesize new tissues Heterotrophic (Soil) Respiration : carbon lost by animals (herbivore) and soil micro-organisms, which convert organic matter back to CO2.
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    3. Terrestrial carbon budget concepts Gross Primary Production (GPP): the total amount of carbon fixed by photosynthesis in an ecosystem. total global GPP estimate: 120 Gt C per yr
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This note was uploaded on 11/07/2011 for the course EAS 8803 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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03_13_Xin - Xin Xi March 13, 2008 Basis 1. Photosynthesis...

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