Energy Exchanges Net Radiation Incident at the Surface...

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GEOG 401 Terrestrial Ecosystem Processes

Terrestrial Ecosystem Processes

•  Energy Balance •  Water Cycling •  Carbon Cycling

Rn = K↓ 1−α( )+ εL↓−εσTs4( )

K↓ αK↓ L↓ 4sTεσ

εL↓Veg Layer

Soil

Net Radiation Incident at the Surface Energy Exchanges

1−α( )K↓

Soil Heat Flux (G)

K↓ L↓ 4sTεσ

G

εL↓

•  Upward and downward conduction of sensible heat •  Driven by vertical temperature gradient in soil •  Modulated by soil thermal properties •  Direction of gradient changes as surface

temperature changes •  Averages near zero over 24-hour period

Energy Exchanges

αK↓

1−α( )K↓

2

Biomass Heat Storage (J)

K↓ L↓ 4sTεσ

εL↓

•  Gain and loss of sensible heat by vegetation •  Observed as heating of biomass during the day and

cooling at night •  Affected by vegetation density, leaf area, stem diameter

and number, net radiation, air temperature, etc. •  Averages near zero over 24-hour period

J

G

Energy Exchanges

αK↓

1−α( )K↓

Photosynthesis (P)

K↓ L↓ 4sTεσ

εL↓

•  Some of solar radiation absorbed by canopy is used for photosynthesis, storing that energy in the form of chemical compounds

•  Generally, P is small enough to be ignored for energy balance purposes

•  P of C4 grasses (e.g. sugarcane) can be significant

J P

G

Energy Exchanges

αK↓

1−α( )K↓

K↓ L↓ 4sTεσ

H Eλ

G

Surface Energy Balance

εL↓ J P

•  Sensible energy (H) and latent energy (λE) are major components of the energy balance

•  The partitioning between H and λE is determined by surface characteristics, especially vegetation type and moisture availability

Energy Exchanges

αK↓

1−α( )K↓

Rn = K↓ 1−α( )+ εL↓−εσTs4( ) = H +λE +G + J +P

K↓ L↓ 4sTεσ

H Eλ

G


εL↓ J P

Radiative Exchange

Storage

Turbulent Flux

Energy Exchanges

αK↓

1−α( )K↓

3

Rn = H +λE +G + J

K↓ L↓ 4sTεσ

H Eλ

G


εL↓ J P

Radiative Exchange

Storage

Turbulent Flux

Photosynthesis can generally be ignored.

X

Energy Exchanges

αK↓

1−α( )K↓

K↓ L↓ 4sTεσ

H Eλ

G


εL↓ J P

Radiative Exchange

Storage

Turbulent Flux

Rn = H +λE

X X X

For 24-hour or multi-day periods, other storage terms (G and J) can be ignored. This allows the energy balance equation to be simplified:

Energy Exchanges

αK↓

1−α( )K↓


EHRn λ+=

nR

H

λE

Energy Partitioning

Energy Exchanges

-100

0

100

200

300

400

500

600

700

0:00 4:00 8:00 12:00 16:00 20:00 0:00

Kd

Rn

EH

G

Brazil: Bare Soil-1000

100200300400500600700800900

0:00 4:00 8:00 12:00 16:00 20:00 0:00

Thailand: 25-yr Secondary Vegetation

Kd

Rn

E

H

G


Energy Exchanges

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Energy Exchanges

Diurnal Cycles Energy Exchanges

Regional Energy Balance Energy Exchanges

MMMeeeaaannn eeennneeerrrgggyyy fffllluuuxxxeeesss...

Site Rn G E H day all day all day all day all

Thailand (l) Harvested barley 265 116 18 6 68 21 193 96 (m) Fallow rice paddy 306 150 27 1 171 93 56 30 (n) Irrigated bare soil 322 152 31 5 266 171 33 -18 (o) 2-yr Secondary veg 162 72 2 0 155 90 19 -8 (p) 3-yr Secondary veg 235 100 10 4 144 80 79 14 (q) 8-yr Secondary veg 318 136 0 -3 313 158 7 -18 (r) 25-yr Secondary veg 297 141 2 0 274 168 9 -27 + Day refers to 12-hour period 6:00 - 18:00

Surface Energy Balance Energy Exchanges

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Ecosystem Processes Controlling Water Cycling

Water Cycling

•  Evapotranspiration (link to energy cycling) •  Transpiration •  Rainfall interception -  Wet canopy evaporation -  Throughfall -  Stemflow

•  Cloud water interception •  Influences on soil hydraulic properties

Ecosystem Water Balance

RF Irr

GWR

ET - Transpiration - Wet canopy evaporation - Soil evaporation

RO ΔSM

CWI

Water Cycling

Stoma Leaf stomata (stoma) are important in controlling fluxes of water, energy, and carbon dioxide

Water Cycling

Stoma

Pea Leaf Stoma, Vicea sp. (SEM x3,520). This image is copyright Dennis Kunkel at www.DennisKunkel.com

Water Cycling

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Stomata

Water Cycling

Ohm’s Law Analogy for Heat Water and CO2 Exchanges by Leaves

Bonan (2008, Figure 16.2)

Water Cycling

Latent Heat of Vaporization λ = 2.454 x 106 J kg-1 at 20ºC

Typical summer evap. rate: 5 mm per day Water density: 1000 kg m-3 5 mm = 5 kg per square meter

22 mW142

kgJ2454000

s 86400day 1

daymkg5 =××

Water Cycling

Latent Heat of Vaporization λ = 2.454 x 106 J kg-1 at 20ºC

Another way of stating the latent heat of vaporization: The amount of latent heat flux per mm/day of evap:

λ = 28.36 W m-2 per mm day-1

Examples: (a) 5 mm per day:

λE = 5 mm day-1 x 28.36 W m-2 per mm day-1 = 141.8 W m-2

(b) λE = 110 W m-2 : E = 110 W m-2 / 28.36 W m-2 per mm day-1 = 3.88 mm day-1

Water Cycling

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Water Cycling Water Cycling

Rainfall Interception Water Cycling

Measuring Throughfall

Water Cycling

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Measuring Throughfall

Water Cycling

Measuring Stemflow

Water Cycling

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Cloud Water Interception

Water Cycling

Terrestrial Ecosystem Carbon Cycling

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

Adapted from a lecture by Dr. Creighton M. Litton Department of Natural Resources and Environmental Management University of Hawai‘i at Mānoa

Carbon Cycling

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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

•  Forests account for 80% of global terrestrial biomass and 75% of global terrestrial productivity

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

ecosystem processes

Terrestrial Ecosystem Carbon Cycling

Adapted from a lecture by Dr. Creighton M. Litton, NREM, UHM

Carbon Cycling

The“breathing” of Earth

Terrestrial Metabolism


Carbon Cycling

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

• Net photosynthesis (Gross photo - foliage dark 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

Photosynthesis


Carbon Cycling

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

–  Measure a few leaves and scale to the canopy?

→ →

Gross Primary Production


Carbon Cycling

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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 TEM or DGVM



Carbon Cycling

Dynamic Global Vegetation Model

Terrestrial Ecosystem Model

Leaf

Are

a In

dex

Abs

orbe

d PA

R

Light Use Efficiency

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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



Carbon Cycling

•  How do you measure GPP? –  Sum of individual

components •  Need measurements of all the

individual components •  Only ~30 studies worldwide

Litton et al. (2007)



Carbon Cycling

•  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 •  N availability •  Temperature, light, & CO2



Carbon Cycling

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•  How is GPP distributed globally across biomes?

Global Terrestrial GPP Distribution

Biomes GPP


Carbon Cycling

• Net primary production (NPP)

–  Net annual C gain (or loss) by plants

–  NPP = GPP – Rplant

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

Net Primary Production


Carbon Cycling

•  What controls NPP globally?

Net Primary Production

Running et al. (2004)


Carbon Cycling

•  How is NPP distributed globally across biomes?

Global Distribution of Net Primary Production

Biomes NPP


Carbon Cycling

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•  How is NPP distributed globally across biomes?

Global Distribution of Net Primary Production

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 ½ of

global biomass and 1/3 of NPP Adapted from a lecture by Dr. Creighton M. Litton, NREM, UHM

Carbon Cycling

•  Rplant = Rgrowth + Rmaint + Rion

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

–  Why does living biomass respire? •  Provides energy for essential metabolic processes

–  Mitochondrial oxidation of CHO’s to make ATP

–  Not “wasted” C

Respiration


Carbon Cycling

•  Rgrowth (growth/construction) –  C in new biomass + C used to

generate that biomass = total C cost

–  Similar across species –  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

Respiration


Carbon Cycling

•  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

Respiration


Carbon Cycling

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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)

Respiration


Carbon Cycling

• 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

Ecosystem Carbon Balance


Carbon Cycling

• 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

Ecosystem Carbon Balance

Litton & Kauffman (2008)

Metrosideros polymorpha


Carbon Cycling

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

loss) by an ecosystem

–  NEP = GPP – Recosystem

–  NEP = NPP – Rhetero

•  Same as NEE???

–  What are we missing?

Net Ecosystem Production


Carbon Cycling

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•  Net biome production (NBP) –  Net ecosystem C gain

(or loss) by large regions over long time scales

–  NBP = NEP ± Flateral - Fdisturb - Fleach - Femissions

•  Information most useful for C sequestration estimates

•  Both natural & anthropogenic disturbances

Net Biome Production


Carbon Cycling

•  TBCA (Total Belowground Carbon Allocation) –  Measuring BNPP and Rbelow is exceedingly difficult

•  Would also miss a lot of C that goes to other components –  TBCA is the total amount of C that plants allocate

belowground •  Root production + root respiration + C to symbionts +

rhizodeposition

–  Based on conservation of mass •  Direct measurements of all inputs & outputs of C except

the one you can’t measure and you want to solve for –  TBCA = FS + FE - FA + ΔCS + ΔCR + ΔCL

Carbon Allocation


Carbon Cycling

See: http://nrs.fs.fed.us/pubs/jrnl/2002/nc_2002_giardina_001.pdf

•  TBCA (Total Belowground Carbon Allocation) –  TBCA is as easy as taking a bath…

Carbon Allocation

Giardina & Ryan (2002)


Carbon Cycling

•  High LAI is needed to maximize GPP (or NPP), yet LAI is largely constrained by aboveground and belowground resource availability

•  How do plants deal with this dilemma? –  Alter allocation in response to resource availability

•  Allocate growth and biomass to aboveground to maximize C gain

•  Allocate growth and biomass to belowground to maximize belowground resource capture

Carbon Allocation


Carbon Cycling

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•  Liebig’s Law of the Minimum –  Plants allocate growth to tissues that maximize

capture of the single most limiting resource •  Allocate to roots when substrate is dry or nutrient poor •  Allocate to stem (&/or leaves) when light is limiting

–  (a) more biomass, (b) more efficient, and/or (c) longer retention

•  Plants constantly adjust allocation –  Prevents overwhelming limitation by one resource –  Tends to result in plants being limited by multiple

resources

Carbon Allocation


Carbon Cycling

•  Do global patterns exist for C allocation? –  Litton et al. (2007) examined a diverse global

dataset of forest stand C budgets –  Divided allocation into 3 separate components:

•  Biomass (the amount of organic material present) •  Flux (the flow of carbon to a given component per unit

time) •  Partitioning (the fraction of GPP used by a given

component)

Carbon Allocation


Carbon Cycling

•  Global forest C allocation patterns –  Biomass ≠ flux or

partitioning –  Why? –  Does C storage = C

sequestration? •  C storage ≠ C

sequestration!!!!!!!!


Carbon Allocation


Carbon Cycling

•  Global forest C allocation patterns –  R uses a ~constant fraction

of GPP


Terrestrial Ecosystem Carbon Exchange


Carbon Cycling

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•  Global forest C allocation patterns –  As resources (GPP) increase,

partitioning shifts from below- to aboveground

–  Partitioning to foliage is ~constant

•  An increase in resources increases partitioning to wood




Carbon Cycling

• Disturbance & succession are major causes of variation in C storage and C sequestration rates


or

Wardle et al. (2004)

Barnes et al. (1998)


Carbon Cycling

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