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Carbon dynamics: perspectives from ecosystem models Sarah C. Davis Interface Meeting, Captiva Island Fl March 2, 2011 Major challenges • Long-term responses to climate change • Effects of land use change Outline • Approach to modeling • Carbon trends in perennial grass crops – belowground carbon sequestration • Land use issues and challenges • Carbon dynamics in forested ecosystems – aboveground carbon sequestration • Resolving long term responses of forests to climate change Ecosystem modeling approach • Comparative ecosystem physiology • Comparative ecosystem biogeochemistry • Coupled to hypothesis-driven research Example of a physiology-driven model (PnET) GPP Maximum gross photosynthesis Realized gross photosynthesis Net photosynthesis VPD Radiation Leaf nitrogen content NPP Basal respiration PAR daylength Day temperature Night temperature Realized respiration Example of biogeochemistrydriven model Miscanthus x giganteus Parton et al. 1998 Above- vs. Below-ground Carbon Sinks • “Judicious management” can increase soil C – Lugo et al., 1986, Cerri et al. 1991, Izaurralde et al. 2000, Conant et al. 2001, Zan et al. 2001, Lal 2004 • Long-term carbon sequestration more dependent on increasing aboveground biomass – Schlesinger 1990, Richter et al. 1999, Schlesinger and Lichter 2001 Ecosystem Models productivity Ecosystem CO2 Atmospheric Tools for characterizing effects of both climate change and land use change Ecosystem productivity Biomass Atmospheric Harvest CO2 Miscanthus and Switchgrass Davis , Parton et al. 2011 in press Net Greenhouse Gas Fluxes Corna -2 gC m yr -1 Switchgrass c no fertilizer b Miscanthus Switchgrass fertilizer d < -450 -450 to -300 -300 to -150 -150 to -75 -75 to -50 -50 to -25 -25 to 25 25 to 50 > 50 Davis , Parton et al. 2011 in press Soil Carbon Corn a gC m-2 < 2000 Switchgrass no fertilizer c Miscanthus b Switchgrass fertilizerd 2000 - 2250 2250 - 2500 2500 - 2750 2750 - 3000 3000 - 3500 3500 - 4000 4000 - 4500 4500 - 5000 > 5000 Davis , Parton et al. 2011 in press Land Use Change • • • • A controversial issue for biofuels Scaling beyond the case study is very difficult Political forces are sometimes inhibitory We need internationally standardized land use monitoring and databases – See Davis et al. 2011 in Journal of the Royal Society Interface Eastern US Forest Carbon Sink • Regenerating forests – Caspersen et al. 2000, Schimel et al. 2000, McGuire et al. 2001, Hurtt et al. 2002, Goodale et al. 2002, Houghton 2003, Nabuurs et al. 2003 • Climate change – Schimel 1995, Cao & Woodward 1998, Kicklighter et al. 1999, Joos et al. 2001, Joos et al. 2002, McGuire et al. 2001 Loblolly Pine Production Wood Production (g m-2 y1) 1800 1600 Modeled 1400 Measured 1200 1000 800 600 400 200 0 0 20 40 60 Age (years) 80 100 120 Pine Plantation Harvests How do forested respond to climate change over time? Loblolly pine production over time Drake, Davis, Raetz, DeLucia 2010 Global Change Biology Photosynthetic Response to CO2 Ca = 12CO2 + 13CO2 Ci Ci :Ca is proportional to photosynthesis (A) Lower Ci:Ca means more 13C is assimilated Do young and old forests respond similarly to climate change? Old forests have experienced the changing atmospheric CO2 concentration Is the gradual response to CO2 over a century similar to the instantaneous response? Historical response vs. Projected Response 0.8 y = 0.672e0.0002x R² = 0.0749 Ci:Ca 0.7 0.6 y = 0.639e-0.002x R² = 0.7237 0.5 Ca in current year Ca in establishment year 0.4 0 25 50 75 Forest Age (y) 100 125 Physiological Constraints on Response to CO2 vary over time Linear (Young) 1.5 1.4 1.4 1.3 1.3 1.2 1.2 1.1 1.1 1.0 delAmax at 458 ppm CO2 Ci:Ca in current year Ci:Ca in establishment… Linear (Old) 27 Amax 22 17 12 7 0 25 50 75 Forest Age (y) 100 125 380 580 780 980 1180 Atmospheric CO2 1380 Summary • Soil carbon sequestration is greater in perennial crops than row crops. • There is a need for internationally standardized land use data. • Older forests may be more responsive to increases in atmospheric CO2 than younger forests. Acknowledgements • • • • • • • • • Steve Del Grosso Evan DeLucia John Drake Cindy Keough Ernest Marx Tim Mies Steve Long Bill Parton Lisa Raetz