The global Carbon Cycle-

The Terrestrial Biosphere

Dr. Peter KöhlerE-mail: pkoehler@awi-bremerhaven.de

Monday, 21.11.2005, 11:15 – 13:00Room: S 3032

My background: PhD in Physics, Research: modelling of forest growth, biodiversity, global vegetation, glacial/interglacial variation in the carbon cycle

• GPP (gross primary production through photosynthesis) ~ 120 PgC/yr

• RA (autotrophic respiration) vegetation ~60

PgC/yr

• NPP = GPP -RA (net primary production) ~

60 PgC/yr

• RH (heterotrophic respiration) humus and soil

~ 55 PgC/yr

• NEP = NPP – RH (net ecosystem production)

~ 5 PgC/yr

• NBP = NEP – disturbances (fires, etc) ~ 1 PgC/yr (net biome production)

Shortcut – terrestrial carbon cycle

IPCC 2001

gC/(m2 * yr)

Photosynthesis 1 – C3 plants (Calvin cycle)

• M. CALVN and his collaborators at the University of California, Berkeley were able to reveal completely the reactions taking place during the incorporation of carbon dioxide into carbohydrates in the relatively short period from 1946 – 1953

• A complex process for the net equation:

6H20 + 6 CO

2 -> C

6H

12O6 (Glucose) + O

2

The Calvin Cycle proceeds in three stages (C3):1. Carboxylation - CO2 is covalently linked to a carbon skeleton (RuBP)2. Reduction - carbohydrate is formed at the expense of ATP and NADPH3. Regeneration - the CO2 acceptor RuBP reforms at the expense of ATP

Main enzyme: RubiscoHttp://www.biologie.uni-hamburg.de/b-online/e24/5.htm

Photosynthesis 2 – C4 plants

In C4 plants an initial step preceeds the Calvin cycle (-> 4 steps =C4)

C4 plants photorespiration is lower than in C3 plants (respiration during photosynthesis).

C4 plants: maize, sugarcane, some tropical grasses

C3 plants: all trees, temperate grasses

Isotopic fractionation of 13C during photosynthesis differs for C3 and C4 plants:(C3) = -15 to -23 o/oo versus (C4) = -2 to -8 o/oo

Isotopic Fractionation 1

13Csample

= ((13C/12Csample

)/(13C/12Cstd

) – 1) * 1000

13C/12Cstd

= 0.0112372 per definition

average CO2 in atmosphere: 13C

atm = -8.0 o/oo (permil)

carbon fixed by C3 plants: 13C

C3 ~ 13C

atm + (C3) = -8 o/oo-20 o/oo = -28 o/oo

carbon fixed by C4 plants:

13CC4

~ 13Catm

+ (C4) = -8 o/oo-5 o/oo = -13 o/oo

Physical process behind: The molecule enriched in 13C is heavier and is therefore discriminated during exchange processes

(heavier~slower in its movements)

Isotopic fractionation 2Fractionation is species specific and 13C is therefore used to identify thoses plant species

involved in exchange processes

2 reservoir system

C2 = C0 + C1

C0: background CO2;

C1: respiration flux of reservoir (plants, soil) to atmosphere

C2: resulting CO2 after exchange process

d13C2 * C2 = d13C0 * C0 + d13C1 * C1

d13C2 = C0 (d13C0 – d13C1) * 1/C2 + d13C1

y = m * x + b

linear equation between new d13C2 and 1/C2, with d13C1 as y-axis intercept,

called KEELING PLOT

Keeling plot (C.D.Keeling (1958))

Pataki et al 2003

Two important limitations:• 2 reservoir system• Fast process

Keeling plot 2

Seasonal cycle in atm 13C, CO2 has its origin in the

variability of the terrestrial biosphere (d13C0 ~ -25 o/oo)

C3 vs C4 plants

• Increase in CO2 favours C3 plants

• Crossover temperature: quantum yield for CO

2 fixation is equal for

C3 and C4

• Warmer temperature favours C4 plants

• Depends also on precipitation

Köhler & Fischer 2004

Holdridge's Life Zones (1967)• Distribution of Biomes

(ecosystems defined by dominated types) defined by

– Mean annual temperature

– Precipitation

– Evapotranspiration

Remote sensing – Tree cover

DeFries et al. 2000

Remote sensing – a) evergreen b) deciduous

DeFries et al. 2000

Remote sensing – a) broadleaf b) needleleaf

DeFries et al. 2000

Dynamic Terrestrial Vegetation Models DGVM

Global vegetation model include fundamental processes on different levels (photosynthesis, respiration, allocation, disturbances)

Global vegetation model include fundamental processes on different levels (photosynthesis, respiration, allocation, disturbances)

Global vegetation model include fundamental processes on different levels (photosynthesis, respiration, allocation, disturbances)

Species need to be grouped into so-called Plant Functional Types (PFT), typically 10 – 20 globally.

Plant Functional Types in LPJ-DGVMLund-Potsdam-Jena DGVM

no. PFT name

1 Tropical broadleaved evergreen tree

2 Tropical broadleaved raingreen tree

3 Temperate needle-leaved evergreen tree

4 Temperate broadleaved evergreen tree

5 Temperate broadleaved summergreen tree

6 Boreal needle-leaved evergreen tree

7 Boreal summergreen tree

8 C3 grass

9 C4 grass

Carbon in Vegetation (LPJ)

Carbon in Soil (LPJ)

Total Carbon (LPJ)

Applications

• Anthropogenic changes– land use change– Terrestrial carbon sink

– CO2 fertilisation

• Glacial terrestrial carbon storage

•pCO2 measureed

•Land biotic uptake: Photosynthesis increases O

2/N

2 ratio

•Fossil fuel: From known usage

•-> Residual must be oceanic uptake

Data-based estimate of anthropogenic impact

After Marland et al 2005, Houghton 2003

Cumulative input:•Fossil fuels 284 PgC•Land use 181 PgC•Sum 465 PgC

Cumulative uptake:•Atmosphere 150 PgC•Ocean 106 PgC•Terrestial B 209 PgC (most uncertain)

CO2 fertilisation

Experiments show species specific response to elevated CO

2. Uptake rates seem to increase, but

also the respiration rates: Storage in plants not necessary increased. Soils important.

Körner et al 2005

Glacial terrestrial carbon storage

4 main factors

(preindustrial-last glacial maximum

LGM (~20,000 yr BP)):

– Rising land ice sheets -600 PgC

– Drop in sea level (-120 m) +200 PgC

– Drop in dT (-(5-10)K) +250 PgC

– Drop in CO2 (-80 ppmv) -650 PgC

– Total -800 PgC

Range given by various studies (d13C, pollen-based vegetation reconstructions, modelling):

– -(300-1000) PgC

Köhler et al 2005