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Title: MODELING A SPRING WHEAT CROP UNDER ELEVATED CARBON DIOXIDE AND DROUGHT

Author
item GROSSMAN-CLARKE, S - ARIZONA STATE UNIV
item Pinter Jr, Paul
item KARTSCHALL, T - POTSDAM INSTITUTE
item Kimball, Bruce
item Hunsaker, Douglas - Doug
item Wall, Gerard - Gary
item GARCIA, R - LI-COR INC
item LAMORTE, R - USDA-ARS-USWCL - PHOENIX

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2001
Publication Date: 6/6/2001
Citation: Grossman-Clarke, S., Pinter Jr, P.J., Kartschall, T., Kimball, B.A., Hunsaker, D.J., Wall, G.W., Garcia, R.L., Lamorte, R.L. 2001. Modeling a spring wheat crop under elevated carbon dioxide and drought. New Phytologist. 150(2):315-335.

Interpretive Summary: The carbon dioxide (CO2) concentration of the atmosphere is expected to double near the end of the 21st Century and is likely to have significant effects for many agricultural crops including wheat, one of the world's most important food sources. The magnitude of these CO2 effects and the extent to which they will alter the water requirements, growth, and yield of wheat are likely to be influenced by other environmental factors such as temperature and precipitation that also are expected to vary in the future. To examine the interactive effects of all of these factors on wheat productivity and to help formulate strategies to deal with global change, the crop simulation model DEMETER was tested using the results from Free Air Carbon dioxide (FACE) experiments conducted at the Maricopa Agricultural Center, Maricopa, Arizona. The model simulation showed that elevated CO2 resulted in greater productivity and grain yield under drought conditions because plants had a lower rate of water use, produced a greater root mass, and were more efficient in photosynthesis. The contribution of these different mechanisms changed in significance during the growing season. The results of this study show that a well-tested simulation model can be a useful research tool for understanding the complex interactions underlying observed crop responses to water stress under elevated CO2 and in predicting the effect that global change will have on crop productivity in the future. This study will benefit researchers, policymakers, and ultimately consumers of wheat and wheat products.

Technical Abstract: The model DEMETER was used to determine which mechanisms led to a higher CO2 effect on biomass production and yield of a spring wheat crop under drought compared to unlimited water supply. Field data of the Free-Air Carbon Dioxide Enrichment wheat experiments in Arizona(1993-94) were used to test the model. The influence of a particular mechanism leading to a higher CO2 effect under drought was investigated by eliminating the influence of the other causes on the simulation results on selected days during the growing seasons. A higher CO2 effect under drought was caused in the model by the lower potential transpiration rate, higher root biomass and the non-linear functional dependence of net assimilation rate on leaf internal CO2 concentration. The contribution of the different mechanisms changed in significance during the growing season. A well-tested simulation model can be a useful tool in understanding the complex interactions underlying observed ecosystem responses to stress under elevated CO2.