William H. Schlesinger Nicholas School of the Environment and Earth Sciences Duke University The Global Carbon Cycle and the Duke Forest Free-Air CO 2 Enrichment (FACE) Project

Photosynthesis CO 2 + H 2 O CH 2 O + O 2

Nitrogen Budget: Ambient and Elevated CO 2 ComponentAmbientElevated%Change (kg/ha/yr)(kg/ha/yr) __________________________________________________________ Plant Requirement Retranslocation Uptake from Soil __________________________________________________________ Nitrogen-Use Efficiency (NPP/Requirement) __________________________________________________________ (Finzi et. al. 2002)

Chemical Weathering by Carbonation CO 2 + H 2 O H + + HCO 3 - H 2 CO 3 2NaAlSi 3 O 8 + 2H 2 CO 3 + 9H 2 O 2Na + + 2HCO H 4 SiO 4 + Al 2 Si 2 O 5 (OH) 4

Soil Solution Chemistry (meq/liter) DepthAmbientElevated Cl 15 cm cm Cations 15 cm cm HCO 3 –Alkalinity 15cm cm Dissolved Silicon 15cm cm

Estimated Groundwater Sink in 2050 Groundwater Flux (Zekster and Loaiciga 1993) 1 x liters/year HCO 3 Concentration at 200 cm Ambient 3 mM = 0.40 x gC/yr Elevated4 mM = 0.52 x gC/yr Net Sink of 5 gC/m 2 /yr or 0.12 x gC/yr worldwide

Carbon Sequestration Due to Growth at High CO 2 (gC/m 2 /yr) ______________________________________________________ Control Elevated Change Beta Factor Stem Biomass **27% Forest Floor **67% Soil Organic Matter 0-15 cm ns 38% cm ns62% Groundwater Flux **31% ______________________________________________________ Total %

Crude, upper-limit estimate of forest uptake by atmospheric CO 2 in 2050 Global NPP in Forests26.9 x gC/yr (Field et al. 1998) Response to FACE in+20% = 5.6 x gC/yr globally …Duke Forest IPCC BAU Emissions15 x gC/yr …Estimate for 2050 Gross Increment of carbon 36% …Uptake by Forests _____________________________________________________________