Terrestrial Ecosystem Carbon Exchangeclimate.socialsciences.hawaii.edu/Courses/GEOG402/GEOG...Deserts 27.7 10 3.5 Arctic tundra 5.6 2 0.5 Crops 13.5 4 4.1 Ice 15.5 Total 149.3 652

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Terrestrial Ecosystem Carbon Exchange

Dr. Creighton M. Litton Department of Natural Resources and Environmental Management

University of Hawai‘i at Mānoa

•  Objectives –  Terrestrial Ecosystem Carbon Cycling

•  Carbon Input (GPP) •  Autotrophic respiration (R) •  Net primary production (NPP) •  Net ecosystem production (NEP) •  Net Ecosystem Carbon Balance (NECB) •  Belowground C flux (TBCA) •  C allocation & global patterns

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•  Why should we care about C cycling? –  C is the energy currency of all ecosystems

•  Plant (autotrophic) production is the base of almost all food/energy pyramids

•  Central to all ecosystem goods & services

–  Plant C cycling, to a large extent, controls atmospheric CO2 concentrations (& climate)

•  ~4x as much C stored in terrestrial ecosystems as the atmosphere

•  Forests account for ~50% of global terrestrial biomass and ~35% of global terrestrial productivity

–  Plant-derived C fundamental to soil processes •  Belowground resources are a primary control over all

ecosystem processes


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• Terrestrial metabolism: the “breathing” of Earth


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•  C enters via photosynthesis – Gross Primary Production (GPP)

• Net photosynthesis (Gross photo - foliage R during the day)

1. Accumulates in ecosystems (C sequestration) as: (a) plant biomass; (b) SOM & microbial biomass; or (c) animal biomass

2. Returned to the atmosphere via (a) respiration (R; autotrophic or heterotrophic); (b) VOC emissions; or (c) disturbance

3. Transferred laterally to another ecosystem


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•  How do you measure GPP? –  Measure photosynthesis of every leaf in the canopy?

–  Measure a few leaves and scale to the canopy?

→ →


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•  How do you measure GPP? –  Modeling studies

•  LAI estimates from remote sensing or field studies

•  APAR or FPAR •  LUE from existing studies •  Plug it all into a TEMs or DGVM


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•  How do you measure GPP? –  Eddy flux / covariance

•  CO2 sensor above the canopy –  Vertical flux of CO2 is a function

of the covariance of wind velocity and gas concentration

•  Really measure Net Ecosystem Exchange (NEE) –  NEE = GPP - Recosystem


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•  How do you measure GPP? –  Sum of individual

components •  Need measurements of all

individual components •  Only ~30-40 studies globally

Litton et al. (2007)


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•  What controls GPP? –  Within a given set of biotic &

environmental conditions: •  Leaf area

–  LAI (leaf area / unit ground area; m2 m-2)

•  Growing season length •  Nutrient availability (esp. N) •  Temperature, light, & CO2


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•  How is GPP distributed globally across biomes?


Biomes GPP

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•  Net primary production (NPP) –  Net annual C gain (or

loss) by plants

–  NPP = GPP – Rplant

–  ANPP, ANPPwood, ANPPfoliage, BNPP, TNPP, etc.


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•  What controls NPP globally?


Running et al. (2004)

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•  How is NPP distributed globally across biomes?


Biomes NPP

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•  How is NPP distributed globally across biomes?


Global distribution of terrestrial biomes and their total carbon in plant biomassa.

Biome

Area (106 km2) Total C pool (Pg C)

Total NPP(Pg C yr-1)

Tropical forests 17.5 340 21.9Temperate forests 10.4 139 8.1Boreal forests 13.7 57 2.6Mediterranean shrublands 2.8 17 1.4Tropical savannas andgrasslands

27.6 7914.9

Temperate grasslands 15.0 6 5.6Deserts 27.7 10 3.5Arctic tundra 5.6 2 0.5Crops 13.5 4 4.1Ice 15.5Total 149.3 652 62.6

a Data from [Roy, 2001 #3858]. Biomass is expressed in units of carbon,assuming that plant biomass is 50% carbon.• Tropical forests are ~12% of land area, but account for

~50% of global biomass and ~35% of global NPP

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•  Rplant = Rgrowth + Rmaint + Rion

–  What respires? •  All living biomass, all the time

–  Why does living biomass respire? •  Grow new biomass and maintain existing biomass •  Provides energy for essential metabolic processes

–  Mitochondrial oxidation of CHO’s to make ATP

–  Not “wasted” C


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•  Rgrowth (growth/construction) –  Total C cost = C in new

biomass + C used to generate that biomass

–  Varies widely by compound •  Function of concentration & cost •  Protein rich (leaves), structural

(wood), and defense

–  How do you measure Rgrowth? •  ~25% x NPP

–  Total C cost = ~1.23g CHOs per 1 g of biomass produced


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•  Rmaint (maintenance of existing biomass) –  Repair of non-growing tissues

•  Protein turnover (~85%)

•  Membrane lipids •  Rion (transport across membranes)

–  ≥ ½ of Rtotal

–  How do you measure Rmaint? •  Strongly correlated with temperature and N content


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•  Rmaint –  Rm = R0(Q10)(T/10)

–  Rm = 0.0106 x N content

Ryan et al. (2004)

Tw (°C)

Curtis et al. (2005)


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• NPP = GPP - Rplant

• Typically measured on annual time scales • Units of biomass or C / unit area / unit time

• g C m-2 yr-1

• How do you measure NPP? • Remember that we typically get GPP by measuring all the components, including NPP


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• Measuring NPP • NPP = ΔBiomass

• Biomass from allometric equations

• Need to account for biomass increment and loss because plant tissue is continually shed

• NPP = (ΔLeaf Bio. + Leaf Litter) + (ΔWood Bio. + Wood Litter) + (ΔRoot Bio. + Root Litter) • Litterfall quantified with littertraps


Litton & Kauffman (2008)

Metrosideros polymorpha

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•  Net ecosystem production (NEP) –  Net annual C gain (or

loss) by an ecosystem

–  NEP = GPP – Recosystem

–  NEP = NPP – Rhetero

•  Same as NEE???

–  What are we missing?


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•  Net Ecosystem Carbon Balance (NECB) –  Net annual C gain (or

loss) by an ecosystem over long time scales

–  NECB = GPP - Recosystem - Fdisturb - Fleach - Femissions

•  Information most useful for C sequestration estimates

•  Both natural & anthropogenic disturbances


Terrestrial Ecosystem Carbon Exchangeclimate.socialsciences.hawaii.edu/Courses/GEOG402/GEOG...Deserts 27.7 10 3.5 Arctic tundra 5.6 2 0.5 Crops 13.5 4 4.1 Ice 15.5 Total 149.3 652

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