Carbon balance – overviewBio 164/264January 25, 2007

Chris Field• How do plants fix atmospheric CO2 into organic compounds?

• What happens to the carbon after it is fixed in photosynthesis?

• How is the CO2 fixed in photosynthesis returned to the atmosphere?

• What controls the storage of carbon in plants and soils?

Behrenfeld et al. Science 2001

Sabine et al. 2004 SCOPE 62

• Carbon cycle (big picture perspective)– What explains carbon sources and sinks?– How important are ecosystem versus anthropogenic

fluxes?– How will carbon sources and sinks change in the future?– How will these changes influence the trajectory of

climate change?

Components of the carbon cycle

• GPP = photosynthesis by autotrophs– measure with gas exchange

• Ra = respiration by autotrophs– Measure with gas exchange

• NPP = net growth by autotrophs = GPP – Ra– food available for consumers– Measure with harvest or harvest surrogate

• Rh = respiration by heterotrophs– Measure with gas exchange

• NEP = net change in local carbon storage (land)– Often conceived as including little or no influence from

disturbance, especially combustion (NPP- Rh)– Measure with repeated inventories or whole system

gas exchange• NBP = regional change in carbon storage

– NEP minus losses to fire, harvest, and other disturbance

– Measure with repeated inventories

• Export production = transfer of NPP to deep waters (ocean)

– NPP minus heterotrophic respiration• Biological pump, Bicarbonate pump, Alkalinity

Pump– Facilitate the movement of carbon from surface to

deeper waters

Why so much interest in the carbon cycle?

• Climate change:• Food:• Understanding the world we live in:

Global carbon budgets for the decades of 1980s and 1990s

1980s 1990sEmissions(fossil, cement)

5.4 0.3 6.4 0.6

Atmospheric increase 3.3 0.1 3.2 0.2

Ocean-atmosphere flux -1.9 0.5 -1.7 0.5

Land-atmosphere flux -0.2 0.7 -1.4 0.7

Land use change emission

1.7 (0.6 to 2.5) Assume 1.6 0.8

Residual terrestrial sink -1.9 (-3.8 to 0.3)

-3.0 (highly uncertain) 0.7

Schimel et al. 2001

Localizing the sink: Ocean vs. LandTraditional approach:

deconvolution/reconstructionReconstruction : emissions from historical record of human activitiesDeconvolution : land uptake = emissions - atm increase - ocean uptake

Combination: “Missing” sink = reconstruction - deconvolution

Localizing the land sink: N-S CO2 gradient

• The observed gradient is shallower than expected from the distribution of fossil fuel and land use.

• Tans et al. 1990

• W-E mixing is so rapid that meridional gradients are very difficult to detect.

Annual uptake by the land is highly variable

Canadell et al. 2007 ms

GPP– 6 CO2 + 12 H2O + light → C6H12O6 + 6 O2 + 6 H2O– carbon dioxide + water + light energy → glucose + oxygen +

water

• n CO2 + 2n H2O + ATP + NADPH → (CH2O)n + n H2O + n O2

Ra

• What is respiration?– Consumption of carbohydrate to release CO2 and generate

reducing equivalents• Glycolysis and Krebs cycle• In mitochondria

– Consumption of O2 and reducing equivalents to produce ATP

• In mitochondria• 2 different oxidases with very different efficiencies

– Fundamentally different from photorespiration– Provides the energy for biosynthesis, turnover, ion

pumping --- life– Provides carbon skeletons for biosynthesis– Can occur in light or dark

• May be suppressed in light

McCree – de Wit – Penning de Vries – Thornley Paradigm

• Respiration powers growth and maintenance• Growth component should be proportional to growth

rate– With a growth efficiency that depends on the cost of the

tissues

• Maintenance component proportional to demands for:– Protein turnover– Maintenance of ion gradients

• R = RG + RM = gRG + mRM where G and M refer to growth and maintenance

• G = YG(P-RM) =YGP – YGmRW (Thornley 1970)

• Some models add a wastage term for futile cycles and other inefficiencies

Complementary approaches

• McCree: Measure growth and respiration under conditions that allow an empirical separation

• Penning de Vries: Trace known biochemical pathways to calculate potential costs Specific growth rate (g g-1)S

peci

fic

resp

irati

on r

ate

(g g

-

1)

Maintenance resp

dR/dG = growth coef

Penning de Vries• Construction costs

– Component processes• NO3- & SO42- reduction• Active uptake• Monomer synthesis• Polymerization• Tool maintenance• Active mineral uptake• Phloem loading

– starch 1.1 g glucose/g product (YG =0.91)

– Protein: 1.5 g glucose/g product (YG = 0.67)

– Lipid: 3 g glucose/g product (YG = 0.33)

• Maintenance costs– Protein breakdown: 0.13-2 ATP/amino acid– Protein synthesis: 4.5-5.9 ATP/amino acid

– Can be related to tissue N: R = gRG + mR,NN

Alternative oxidase

• 1st observed in thermogenic plants– Tissues warm as a result of high respiration– Pollinator attraction: usually foul-smelling

• Insensitive to cyanide– A powerful inhibitor of cytochrome c oxidase

• Energy coupling efficiency only 1/3 of cytochrome c pathway

• Gene in all angiosperms, many algae, and some fungi

Thermogenic respiration

Seymour, R. S., Gibernau, M. & Ito, K. Thermogenesis and respiration of inflorescences of the dead horse arum Helicodiceros muscivorus, a pseudo-thermoregulatory aroid associated with fly pollination.Functional Ecology  17 (6), 886-894.doi: 10.1111/j.1365-2435.2003.00802.x

NPP

• Major controls from– Growing

season length– Water– Temperature– Nutrients

Baldocchi and Valentini 2004 SCOPE 62

NPP• A simple model for large scale estimates

– NPP = APAR•= FPAR•PAR•– Where APAR = absorbed photosynthetically active

radiation = light us efficiency– FPAR = fraction of PAR absorbed– Monteith demonstrated that for many crops grown under

ideal conditions, is close to 1.4 g biomass per mJ absorbed solar radiation

– Wide range of under naturalconditions

Joel et al 1997

Mean annual terrestrial NPP from 16 models:

~ 55 Pg C yr-1

NP

P g

C m

- 2 y

r- 1

Cramer et al. GCB 1999

Global Primary Production: 9/97 – 8/00

Rh

• Dominated by microorganisms – bacteria and fungi

• Can be aerobic or anaerobic

Rh

• Usually modeled as proportional to soil organic matter

• Soil organic matter often conceptualized as pools with distinct turnover times– Metabolic C: a few days to weeks– Active C: a few months to years– Slow C: several years to decades– Passive C: many centuries

• Influence of temperature, moisture, & “quality”– Quality increases with amount of good stuff (e.g. N) and

decreases with amount of bad stuff (e.g. lignin)

Parton et al. Science 2007

70

65

60

55

50

45

C fl

ux (

Pg)

6050403020100

Simulation year

NPP increase 1%/yr

NPP increase 0.5%/yr

Short dashes - 5 yr residenceLong dashes -- 20 yr residence

NEP/NBP and carbon sinks

• In general, an increase in NPP will produce net C storage

• Amount of storage increases with amount of NPP increase

• Amount of storage increases with turnover time of recipient pools– Allocation to wood

leads to substantial storage

– Allocation to exudate leads to little

products

aquaticforests

croplands

non-forest/non-

crop

In the US:Forests may not dominate land

sinks

• Apparent sink: 0.4 –0.7 Pg/yr• “Real” sink: 0.3-0.6 Pg/yr• Forest fraction: 30%• Aquatic fraction 13%

•Pacala et al. Science 2001

For your reading pleasure

• Field, C. B., M. J. Behrenfeld, J. T. Randerson, and P. Falkowski, 1998: Primary production of the biosphere: Integrating terrestrial and oceanic components. Science, 281, 237-240.

• Behrenfeld, M. J., J. T. Randerson, C. R. McClain, G. C. Feldman, S. O. Los, C. J. Tucker, P. G. Falkowski, C. B. Field, R. Frouin, W. E. Esaias, D. D. Kolber, and N. H. Pollack, 2001: Biospheric primary production during an ENSO transition. Science, 291, 2594-2597.

• Pacala, S. W., G. C. Hurtt, D. Baker, P. Peylin, R. A. Houghton, R. A. Birdsey, L. Heath, E. T. Sundquist, R. F. Stallard, P. Ciais, P. Moorcroft, J. P. Caspersen, E. Shevliakova, B. Moore, G. Kohlmaier, E. Holland, M. Gloor, M. E. Harmon, S. M. Fan, J. L. Sarmiento, C. L. Goodale, D. Schimel, and C. B. Field, 2001: Consistent land- and atmosphere-based US carbon sink estimates. Science, 292, 2316-2319.

• Schimel, D. S., J. I. House, K. A. Hibbard, P. Bousquet, P. Ciais, P. Peylin, B. H. Braswell, M. J. Apps, D. Baker, A. Bondeau, J. Canadell, G. Churkina, W. Cramer, A. S. Denning, C. B. Field, P. Friedlingstein, C. Goodale, M. Heimann, R. A. Houghton, J. M. Melillo, B. Moore, D. Murdiyarso, I. Noble, S. W. Pacala, I. C. Prentice, M. R. Raupach, P. J. Rayner, R. J. Scholes, W. L. Steffen, and C. Wirth, 2001: Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems. Nature, 414, 169-172.

• Gruber, N., P. Friedlingstein, C. B. Field, R. Valentini, M. Heimann, J. E. Richey, P. Romero-Lankao, E.-D. Schulze, and C.-T. A. Chen. 2004: The vulnerability of the carbon cycle in the 21st century: An assessment of carbon-climate-human interactions. in The Global Carbon Cycle: Integrating Humans, Climate, and the Natural World, C. B. Field and M. R. Raupach, Eds. Island Press, Washington. 45-76.

• Sabine, C. L., M. Heiman, P. Artaxo, D. C. E. Bakker, C.-T. A. Chen, C. B. Field, N. Gruber, C. LeQuéré, R. G. Prinn, J. E.Richey, P. Romero-Lankao, J. A. Sathaye, and R. Valentini. 2004: Current status and past trends of the carbon cycle. in The Global Carbon Cycle: Integrating Humans, Climate, and the Natural World, C. B. Field and M. R. Raupach, Eds. Island Press, Washington. 17-44.

• Prentice, I. C. 2001: The carbon cycle and atmospheric carbon dioxide. in Climate Change 2001: The Scientific Basis (Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change).

• Tans, P. P., I. Y. Fung, and T. Takahashi, 1990: Observational constraints on the global CO2 budget. Science, 247, 1431-1438.

More readings• Baldocchi, D., and R. Valentini. 2004: Geographic and temporal variation of carbon exchange by

ecosystems and their sensitivity to environmental perturbations. in The Global Carbon Cycle: Integrating Humans, Climate, and the Natural World, C. B. Field and M. R. Raupach, Eds. Island Press, Washington. 295-316.

• Cramer, W., D. W. Kicklighter, A. Bondeau, B. M. III, G. Churkina, B. Nemry, A. Ruimy, A. L. Schloss, J. Kaduk, and participants of the Potsdam NPP Model Intercomparison, 1999: Comparing global models of terrestrial net primary productivity (NPP): overview and key results. Global Change Biology, 5 supplement, 1-15.

• Parton, W., W. L. Silver, I. C. Burke, L. Grassens, M. E. Harmon, W. S. Currie, J. Y. King, E. C. Adair, L. A. Brandt, S. C. Hart, and B. Fasth, 2007: Global-Scale Similarities in Nitrogen Release Patterns During Long-Term Decomposition. Science %R 10.1126/science.1134853, 315, 361-364.

http://www.epa.gov/globalwarming/What is our contribution to greenhouse gases?

5.3 metric tons C from CO2 per person per year = 19.6 metric tons CO2 per person per year

U.S.: 6.6 metric tons carbon per person per year

Range of US uptake