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The global Carbon Cycle - The Terrestrial Biosphere Dr. Peter Köhler Monday, 21.11.2005, 11:15 – 13:00 Room: S 3032.

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Presentation on theme: "The global Carbon Cycle - The Terrestrial Biosphere Dr. Peter Köhler Monday, 21.11.2005, 11:15 – 13:00 Room: S 3032."— Presentation transcript:

1 The global Carbon Cycle - The Terrestrial Biosphere Dr. Peter Köhler Monday, , 11:15 – 13:00 Room: S 3032 My background: PhD in Physics, Research: modelling of forest growth, biodiversity, global vegetation, glacial/interglacial variation in the carbon cycle

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3 GPP (gross primary production through photosynthesis) ~ 120 PgC/yr R A (autotrophic respiration) vegetation ~60 PgC/yr NPP = GPP -R A (net primary production) ~ 60 PgC/yr R H (heterotrophic respiration) humus and soil ~ 55 PgC/yr NEP = NPP – R H (net ecosystem production) ~ 5 PgC/yr NBP = NEP – disturbances (fires, etc) ~ 1 PgC/yr (net biome production) Shortcut – terrestrial carbon cycle IPCC 2001

4 gC/(m 2 * yr)

5 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: 6H CO 2 -> C 6 H 12 O6 (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 NADPH 3. Regeneration - the CO2 acceptor RuBP reforms at the expense of ATP Main enzyme: Rubisco

6 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 13 C during photosynthesis differs for C3 and C4 plants:  (C3) = -15 to -23 o/oo versus  (C4) = -2 to -8 o/oo

7 Isotopic Fractionation 1  13 C sample = (( 13 C/ 12 C sample )/( 13 C/ 12 C std ) – 1) * C/ 12 C std = per definition average CO 2 in atmosphere:  13 C atm = -8.0 o/oo (permil) carbon fixed by C3 plants:  13 C C3 ~  13 C atm +   (C3) = -8 o/oo-20 o/oo = -28 o/oo carbon fixed by C4 plants:   13 C C4 ~  13 C atm +   (C4) = -8 o/oo-5 o/oo = -13 o/oo Physical process behind: The molecule enriched in 13 C is heavier and is therefore discriminated during exchange processes (heavier~slower in its movements)

8 Isotopic fractionation 2 Fractionation is species specific and 13 C is therefore used to identify thoses plant species involved in exchange processes 2 reservoir system C2 = C0 + C1 C0: background CO 2; C1: respiration flux of reservoir (plants, soil) to atmosphere C2: resulting CO 2 after exchange process d 13 C2 * C2 = d 13 C0 * C0 + d 13 C1 * C1 d 13 C2 = C0 (d 13 C0 – d 13 C1) * 1/C2 + d 13 C1 y = m * x + b linear equation between new d 13 C2 and 1/C2, with d 13 C1 as y-axis intercept, called KEELING PLOT

9 Keeling plot (C.D.Keeling (1958)) Pataki et al 2003 Two important limitations: 2 reservoir system Fast process

10 Keeling plot 2 Seasonal cycle in atm 13 C, CO 2 has its origin in the variability of the terrestrial biosphere (d 13 C 0 ~ -25 o/oo)

11 C3 vs C4 plants Increase in CO 2 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

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13 Holdridge's Life Zones (1967) Distribution of Biomes (ecosystems defined by dominated types) defined by –Mean annual temperature –Precipitation –Evapotranspiration

14 Remote sensing – Tree cover DeFries et al. 2000

15 Remote sensing – a) evergreen b) deciduous DeFries et al. 2000

16 Remote sensing – a) broadleaf b) needleleaf DeFries et al. 2000

17 Dynamic Terrestrial Vegetation Models DGVM 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.

18 Plant Functional Types in LPJ-DGVM Lund-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

19 Carbon in Vegetation (LPJ)

20 Carbon in Soil (LPJ)

21 Total Carbon (LPJ)

22 Applications Anthropogenic changes –land use change –Terrestrial carbon sink –CO 2 fertilisation Glacial terrestrial carbon storage

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25 pCO 2 measureed Land biotic uptake: Photosynthesis increases O 2 /N 2 ratio Fossil fuel: From known usage -> Residual must be oceanic uptake

26 Data-based estimate of anthropogenic impact After Marland et al 2005, Houghton 2003 Cumulative input: Fossil fuels284 PgC Land use 181 PgC Sum465 PgC Cumulative uptake: Atmosphere150 PgC Ocean106 PgC Terrestial B209 PgC (most uncertain)

27 CO 2 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

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29 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 CO 2 (-80 ppmv)-650 PgC –Total-800 PgC Range given by various studies (d 13 C, pollen-based vegetation reconstructions, modelling): –-( ) PgC Köhler et al 2005


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