ORNL is managed by UT-Battelle for the US Department of Energy

Vegetation turnover and nitrogen

feedback drive carbon sequestration

in response to elevated CO2

Anthony Walker, Martin De Kauwe, Belinda Medlyn, Sönke Zaehle , Richard Norby

& the FACE-MDS team

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. NACP Meeting 2015

Predictive understanding? (of terrestrial C sequestration in response to

eCO2)

Land C sequestration

Land C release

11 CMIP5 Earth-System models under 3 scenarios of CO2 coupling

Ocean C sequestration

Ocean C release

Arora et al. (2013) J. of Clim.

4. NACP Meeting 2015

FACE-MDS was set up to evaluate predictive understanding of ecosystem responses to

elevated CO2

5. NACP Meeting 2015

Duke FACEPinus taedaNorth Carolina, USA

Oak Ridge FACE Liquidambar styraciflua - Tennessee, USA

Ambient & elevated CO2 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. 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. NACP Meeting 2015

Simulated productivity and sequestration responses to eCO2 over 300 years

Walker et. al. (in revision) BGC

8. NACP Meeting 2015

Cveg

Csoil

fGveg

.NPP

τveg

Cveg τ

soilC

soil

GPP .CUE

Equilibrium ecosystem carbon sequestration analysis

9. NACP Meeting 2015

Equilibrium biomass response to eCO2 is driven by productivity & turnover responses

Walker et. al. (in revision) BGC

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 (Nup) multiplied by the N use efficiency of the plant (NUE).

NPP = Nup x NUE

NPP = Nup x NPP/ Nup

N uptake is a major driver of uncertainty in projections of productivity NPP = Nup x

NUE

Years after start of eCO2: 5 100 295 5 100 295 5 100 295

eCO

2 r

espo

nse

(%)

GDAY

CABLE

PNL

CLM4

LPJ-GUESS

O-CN

No PNL

Walker et. al. (in revision) BGC

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. 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. NACP Meeting 2015

ΔNPP ΔNup ΔNUE

Year 1 post eCO2 Final year – initial year

ΔNPP ΔNup ΔNUE

NPP = Nup x NUE

Nup 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. NACP Meeting 2015 De Kauwe et. al. (2014) New Phyt.

Model evaluation: Allocation at Oak Ridge

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. 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 eCO2

N uptake

Shinichi Asao Ram Oren Tom BodenMichael Dietze Colleen Iversen Bai Yang

Bassil El-Masri Heather McCarthy Xia SongAnna Harper Jeff Warren Lynn TharpThomas Hickler Lynn Fenstermaker And many others …Atul Jain Bob NowakChris Lu Jack MorganYiqi Luo Dan LecainKristina Luus Pat MegonigalWilliam Parton Bruce HungateColin Prentice Lu MengDan Ricciuto Elise PendalShijie Shu Ed RyanPeter Thornton Mark Schimelpfenig

Shusen Wang Don Zak

Ying-Ping Wang Andy Burton

David Wårlind Alan Talhelm

Ensheng Weng Rima Upchurch

Cristian Werner David Ellesworth

Jianyang Xia Adrien Finzi

Ryan Pavlick Anne Gallet-Budynek

Thanks to:

Data:cdiac.ornl.gov/face

FACE-MDS Phase 2