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ATMOS 397GATMOS 397GBiogeochemical Cycles and Global ChangeBiogeochemical Cycles and Global Change

Lecture 10: Carbon CycleLecture 10: Carbon Cycle

Don WuebblesDon Wuebbles

Department of Atmospheric SciencesDepartment of Atmospheric Sciences

University of Illinois, Urbana, ILUniversity of Illinois, Urbana, IL

February 4, 2003February 4, 2003

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Per capita

Honduras – CO2 Emissions

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Why are plants green?Why are plants green?

Absorption spectrum of isolated chlorophyll and carotenoid species.

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PhotosynthesisPhotosynthesis

Photosynthesis occurs in organelles called

CHLOROPLASTS

2 Stage Process

Water vapor split high energy molecules formed

— 2H2O 4H+ + O2 (note production of O2)

— NADP NADPH and ADP ATP

Reduction of CO2 by H atoms

— The Calvin Cycle

Net:

6 CO2 + 6H2O --------> C6H12O6 + 6 O2

(glucose)

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Photosynthesis: The Calvin cyclePhotosynthesis: The Calvin cycle

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PhotosynthesisPhotosynthesis

Overview of photosynthetic processes as they occur in plants, algae, and cyanobacteria.

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Flow Chart for PhotosynthesisFlow Chart for Photosynthesis

Photosynthesis (Flow Chart)  

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At nightAt night

The light reactions of photosynthesis stop

when the sun goes down.

However, CO2 fixation can continue as

long as ATP and NADPH is available.

In cacti and other succulents CO2 uptake

by the plant occurs primarily at night.

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April 2001

September 2000

December 2000

0 0.90.5

MODIS FPAR(Fraction of absorbed Photosynthetically Active Radiation)

FPAR is defined as the fraction of incident photosynthetically active radiation (0.4 - 0.7 m) absorbed the vegetation canopy.

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RespirationRespiration

Respiration: oxidation of carbohydrate to CO2

and H20 in living cells is generally termed

respiration Reverse reaction mechanism

Approx. half of the gross carbon fixation by photosynthesis is used by the plants.

As a result, actual rate of photosynthesis is about twice that which is measured by plant growth

Respiration Photosynthesis

Energy Released Stored

Reactants Glucose CO2 and H2O

Products CO2 and H2O Glucose

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Gross Primary Productivity – Europe (Jan 25 – Feb 1, 2001Gross Primary Productivity – Europe (Jan 25 – Feb 1, 2001

From MODIS satellite instrument

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Net Primary ProductionNet Primary Production

NPP = Uptake of carbon by photolysis – autotrophic respiration losses by vegetation

NPP = Gross Primary Production – plant respiration

or

NPP = GPP - Rp

Annual accumulation of organic matter per unit of land is a measure of NPP

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Net Ecosystem ProductivityNet Ecosystem Productivity

NEP = NPP – Respiration losses from soil

NEP is an estimate of the carbon fluxes between the ecosystem and the atmosphere.

The soil respiration losses are caused by the heterotrophic decomposition of soil organic litter.

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Major Terrestrial Biomes Major Terrestrial Biomes

Savannah –Cabazo, Venezuala

Desert – New Mexico

Boreal Forest - Finland

                                             <>

Tropical Forest - Malaysia

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Average annual Net Primary Productivity of the Average annual Net Primary Productivity of the

Earth's major biomesEarth's major biomes

 Ecosystem Type Net Primary Productivity

(kilocalories/meter-2/year)  Tropical Rain Forest  9000

 Estuary  9000

 Swamps and Marshes  9000

 Savanna  3000

 Deciduous Temperate Forest

 6000

 Boreal Forest  3500

 Temperate Grassland  2000

 Polar Tundra  600

 Desert  < 200

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Factors Limiting NPPFactors Limiting NPP

All plants require sunlight, carbon dioxide, and water for photosynthesis. Photosynthesis is also dependent on temperature and soil nutrients. Temperature (heat) controls the rate of plant metabolism which in turn determines the amount of photosynthesis that can take place. Most biological metabolic activity takes place within the range 0 to 50 degrees Celsius. There is little activity above or below this range. The optimal temperatures for productivity coincide with 15 to 25 degrees Celsius optimal range of photosynthesis. Shown is the relationship between the net primary productivity of forests with annual air temperature and precipiatation.

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IBIS Model – from Jon Foley

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