1. 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

7. Photosynthesis CO 2 + H 2 O CH 2 O + O 2

22. Nitrogen Budget: Ambient and Elevated CO 2 ComponentAmbientElevated%Change (kg/ha/yr)(kg/ha/yr) __________________________________________________________ Plant Requirement51.961.518.5 Retranslocation28.631.510.2 Uptake from Soil23.330.028.9 __________________________________________________________ Nitrogen-Use Efficiency2923116.6 (NPP/Requirement) __________________________________________________________ (Finzi et. al. 2002)

29. 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 3 - + 4H 4 SiO 4 + Al 2 Si 2 O 5 (OH) 4

30. Soil Solution Chemistry (meq/liter) DepthAmbientElevated Cl 15 cm0.040.05 200 cm0.100.17 Cations 15 cm0.360.41 200cm0.762.82 HCO 3 –Alkalinity 15cm0.130.13 200cm0.641.68 Dissolved Silicon 15cm0.070.08 200cm0.280.35

31. Estimated Groundwater Sink in 2050 Groundwater Flux (Zekster and Loaiciga 1993) 1 x 10 16 liters/year HCO 3 Concentration at 200 cm Ambient 3 mM = 0.40 x 10 15 gC/yr Elevated4 mM = 0.52 x 10 15 gC/yr Net Sink of 5 gC/m 2 /yr or 0.12 x 10 15 gC/yr worldwide

32. Carbon Sequestration Due to Growth at High CO 2 (gC/m 2 /yr) ______________________________________________________ Control Elevated Change Beta Factor Stem Biomass 397 505108 **27% Forest Floor 78 13052 **67% Soil Organic Matter 0-15 cm 72 9927 ns 38% 15-30 cm 21 3413 ns62% Groundwater Flux 16 215 **31% ______________________________________________________ Total 584 78920535%

34. Crude, upper-limit estimate of forest uptake by atmospheric CO 2 in 2050 Global NPP in Forests26.9 x 10 15 gC/yr (Field et al. 1998) Response to FACE in+20% = 5.6 x 10 15 gC/yr globally …Duke Forest IPCC BAU Emissions15 x 10 15 gC/yr …Estimate for 2050 Gross Increment of carbon 36% …Uptake by Forests _____________________________________________________________