Global Carbon Budget

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. 2010. Update on CO2 emissions. Nature Geoscience Global Carbon Project (2010)

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

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

NECB Chapin et al. 2006

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

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

Vegetation controls of NPP Leaf Biomass Leaf Area Index

Environmental controls on net primary production PRECIPITATION

Precip, NPP, and LAI

TEMPERATURE Great Plains Grasslands Precipitation held constant

BOTH PRECIPITATION AND TEMPERATURE Actual Evapotranspiration (AET)

OTHER CONTROLS NUTRIENTS GRAZING

TEMPORAL PATTERNS SEASONAL

SUCCESSION

SPACE VS. TIME

Global Patterns

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

SEASONAL NEP