2. Global Carbon Budget

3. of the carbon dioxide emitted from anthropogenic sources)
-Natural sinks of carbon dioxide are the land and the ocean (absorb approximately 55%
of the carbon dioxide emitted from anthropogenic sources)
-The strength of these sinks is increasing, but their efficiencies are declining
Friedlingstein et al Update on CO2 emissions. Nature Geoscience
Global Carbon Project (2010)

4. Friedlingstein et al. 2010. Update on CO2 emissions. Nature Geoscience
Global Carbon Project (2010)

5. Primary Productivity
What is it? The rate at which carbon is transferred from its oxidized form
(CO2) to a reduced organic form (and energy is stored) by photosynthesis.
CO2 + H2O  CH2O + O2
Generally expressed in g dry biomass, or g C, / m2 / y OR kcal / m2 / y
Different from biomass which is a static measurement as opposed to a rate.
High biomass  high productivity
Gross Primary Productivity (GPP) is essentially § photosynthesis over time.
Net Primary Productivity (NPP) = GPP - plant respiration (RP or RA)
Net Ecosystem Productivity (NEP) = NPP - heterotrophic respiration (RH) OR
GPP - total ecosystem respiration (RE)
NEP is the net storage of carbon in an ecosystem
NEP > O - sink for C; NEP < 0 source of C

7. NECB
Chapin et al. 2006

10. Can we measure these things?
Aboveground NPP is usually measure by harvesting
Deciduous woody vegetation subsamples of leaves at peak season OR
subsample of litterfall PLUS
increment of wood
Evergreen woody vegetation more difficult yet can distinguish new vs. old
foliar growth by certain traits
Grasslands plant tissue harvested at peak season OR
plant tissue harvested at end of season MINUS
plant tissue harvested at beginning of season
Belowground NPP - difficult
Harvesting - distinguishing between old vs. new roots by color, pliability, suberization
Rhizotron - photographs of roots over time
In-growth Cores

11. Other ways of measuring
Remote sensing - Normalized Difference Vegetation Index
NDVI = (Near InfraRed [NIR] - Red) / NIR + Red

12. Vegetation controls of NPP
Leaf Biomass
Leaf Area Index

13. Environmental controls on net primary production
PRECIPITATION

14. Precip, NPP, and LAI

15. TEMPERATURE
Great Plains Grasslands
Precipitation held constant

16. BOTH PRECIPITATION AND TEMPERATURE
Actual Evapotranspiration (AET)

17. OTHER CONTROLS
NUTRIENTS
GRAZING

18. TEMPORAL PATTERNS
SEASONAL

19. SUCCESSION

20. SPACE VS. TIME

21. Global Patterns

23. What about NEP? Chambers Instrument Towers
NEP can be estimated by measuring CO2 flux.
Chambers
Instrument
Towers

24. SEASONAL NEP