1. ORNL is managed by UT-Battelle for the US Department of Energy Vegetation turnover and nitrogen feedback drive carbon sequestration in response to elevated CO 2 Anthony Walker, Martin De Kauwe, Belinda Medlyn, Sönke Zaehle, Richard Norby & the FACE-MDS team

2. 2. NACP Meeting 2015 Predictive understanding of what? at what scales? with what accuracy? where is there? where do we want to be? are we there yet?

3. 3. NACP Meeting 2015 Predictive understanding? (of terrestrial C sequestration in response to eCO 2 ) Land C sequestration Land C release 11 CMIP5 Earth-System models under 3 scenarios of CO 2 coupling Ocean C sequestration Ocean C release Arora et al. (2013) J. of Clim.

4. 4. NACP Meeting 2015 FACE-MDS was set up to evaluate predictive understanding of ecosystem responses to elevated CO 2

5. 5. NACP Meeting 2015 Duke FACE Pinus taeda North Carolina, USA Oak Ridge FACE Liquidambar styraciflua - Tennessee, USA Ambient & elevated CO 2 treatments, site specific meteorological data, parameterisation, and land use history used to simulate the Duke and Oak Ridge FACE sites: –Experiment simulations for 11 years –Extended simulations for 300 years FACE model-data synthesis (FACE-MDS) Synthesising models & experiments to advance our predictive understanding data: cdiac.ornl.gov/face

6. 6. NACP Meeting 2015 What are the key drivers of model variability in predictions of C sequestration? Can data from FACE experiments inform/constrain these key drivers? Land C sequestration Land C release

7. 7. NACP Meeting 2015 Simulated productivity and sequestration responses to eCO 2 over 300 years Walker et. al. (in revision) BGC

8. 8. NACP Meeting 2015 C veg C soil fG veg.NPP τ veg C veg τ soil C soil GPP.CUEGPP.CUE Equilibrium ecosystem carbon sequestration analysis

9. 9. NACP Meeting 2015 Equilibrium biomass response to eCO 2 is driven by productivity & turnover responses Walker et. al. (in revision) BGC

10. 10. NACP Meeting 2015 Plant productivity (NPP) is constrained by nitrogen (N) such that NPP is equal to the N taken up by the plant (N up ) multiplied by the N use efficiency of the plant (NUE). NPP = N up x NUE NPP = N up x NPP/ N up N uptake is a major driver of uncertainty in projections of productivity NPP = N up x NUE Years after start of eCO 2 : 5 100 295 5 100 295 5 100 295 eCO 2 response (%) GDAY CABLE PNL CLM4 LPJ-GUESS O-CN No PNL Walker et. al. (in revision) BGC

11. 11. NACP Meeting 2015 Key drivers of variability in modelled C sequestration response N uptake (supply & demand vs solely supply) Mortality – self-thinning Allocation – many schemes resulted in increased wood allocation Effect of soil wetness on decomposition

12. 12. NACP Meeting 2015 What are the drivers of model variability in predictions of C sequestration? Can data from FACE experiments inform/constrain these key drivers?

13. 13. NACP Meeting 2015 ΔNPP ΔN up ΔNUE Year 1 post eCO 2 Final year – initial year ΔNPP ΔN up ΔNUE NPP = N up x NUE N up was not well simulated by the models Because models were unable to reproduce priming effects Zaehle et. al. 2014 New Phyt. Model evaluation: N uptake at Duke

14. 14. NACP Meeting 2015 De Kauwe et. al. (2014) New Phyt. Model evaluation: Allocation at Oak Ridge

15. 15. NACP Meeting 2015 Model evaluation: Turnover & mortality Not possible with current dataset –Due to the successional stage of the forests & stochastic distribution of mortality through space and time –Was evidence of less damage in a severe ice storm at Duke Model evaluation: Effect of soil water on decomposition –Model causes not yet fully investigated –Effects in the experiment may be difficult to tease out from priming effects

16. 16. NACP Meeting 2015 Are we there yet? Priming Mortality & Allocation Soil Water Effects on Decomposition The road to predictive understanding of terrestrial C sequestration in response to eCO 2 N uptake

17. Shinichi AsaoRam Oren Tom Boden Michael DietzeColleen Iversen Bai Yang Bassil El-Masri Heather McCarthy Xia Song Anna Harper Jeff WarrenLynn Tharp Thomas Hickler Lynn FenstermakerAnd many others … Atul Jain Bob Nowak Chris Lu Jack Morgan Yiqi Luo Dan Lecain Kristina Luus Pat Megonigal William Parton Bruce Hungate Colin Prentice Lu Meng Dan Ricciuto Elise Pendal Shijie Shu Ed Ryan Peter Thornton Mark Schimelpfenig Shusen WangDon Zak Ying-Ping WangAndy Burton David WårlindAlan Talhelm Ensheng WengRima Upchurch Cristian WernerDavid Ellesworth Jianyang XiaAdrien Finzi Ryan PavlickAnne Gallet-Budynek Thanks to: Data: cdiac.ornl.gov/face FACE-MDS Phase 2