Our common corn under climate change:

How accurately do crop models simulate the impact of CO2

atmospheric concentration on maize yield and water use ?

K. Delusca; JL. Durand; K. Boote; J. Lizaso; R. Manderscheid; HJ. Weigel; A. Ruane; C. Rosenzweig; J. Jones; S. Anapalli; L. Ahuja; B. Basso; C. Baron; P. Bertuzzi; D. Ripoche; C. Biernath; E. Priesak; D. Derynge; F. Ewert; T. Gaiser; S. Gayler; F. Heilein; KC. Kersebaum; SH. Kim; C. Müller; C. Nendel; J. Ramirez; R. Rötter; S. Seidel; A. Srivastava; F. Tao; D. Timlin; T. Twine; K. Waha; E. Wang; H. Webber; Z. Zhao.

Objectives. • Previous asssessment of models showed large variability

in simulation the CO2 response (Bassu et al 2014). • Lack of real test of models against real data. • FACE experiments are rare but some available. - Do models properly simulate CO2 effects on yield ? - Do models simulate well CO2 impacts on water use ? - Do models catch the actual crop physiology of the responses ? - How do we improve models in order to get the actual impact of CO2 ?

Maize sown 2 years (2007 2008). Treatments with rainout shelters or irrigated (+ rainfalls) FACE : circa 550 ppm , from LAI >= 0,5 on. 4 Treatments : Ambient DRY, Ambient Wet, Elevated DRY and Elevated wet

v

--- > A relevant and challenging data set to test models against CO2 effects on Maize crop.

Data for watered - ambient treatments 2007 and 2008 were provided Authors adjusted the cultivar dependant ones parameters for yield, LAI, above ground biomass and water use. Then all treatments simulated using 20 different models by 16 modelling groups.

LAI AMBIENT

LAI ELEVATED

Leaf senescence not fast enough

Simulated Dry plots not dry enough in top soil horizons

CONCLUSIONS Models caught the CO2 impact measured in the experiment: • Showing an effect only in 2008 and under Dry conditions • On LAI. • On grain number. • On above ground biomass. • And no impact on water use But general under-estimate of CO2 impact under dry situations and over-estimate of water use . PERSPECTIVES: -> better simulate evapotranspiration is the challenge

Thank you for your attention