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Title: SIMULATED RESPONSES OF ENERGY AND WATER FLUXES TO AMBIENT ATMOSPHERE AND FREE-AIR CARBON DIOXIDE ENRICHMENT IN WHEAT

Author
item GROSSMAN S - PIK GERMANY
item KARTSCHALL T - PIK GERMANY
item KIMBALL B A - 5344-20-10
item HUNSAKER D J - 5344-20-10
item LAMORTE R L - 5344-20-10
item GARCIA R L - LI-COR
item WALL G W - 5344-20-10
item PINTER JR P J - 5344-20-10

Submitted to: Journal of Biogeography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: In order to predict the consequences of present and future global environmental changes on the security of world food production and on future irrigation requirements, efforts are underway to develop the capability to predict the growth, yield, and water use of major food crops. These global changes especially include the increasing concentration of atmospheric carbon dioxide (CO2) which is expected to double sometime during the next century. Climate modelers have predicted that the elevated CO2 will cause the earth to warm and that precipitation patterns will change. Elevated CO2 is also known to alter the growth of plants and may affect their water requirements. Accordingly, a computer model called DEMETER was developed, which is capable of predicting the growth of a wheat crop and its consumption of water. This paper describes a specific validation test of the model comparing its predictions with actual data from a free-air CO2-enrichment experiment on wheat at CO2 concentrations of 550 ppm and present- day ambient of about 370 ppm. The results showed that the model could track the temperature of the crop hour-by-hour reasonably well, and consistent with the data, future wheat water requirements may decease slightly, perhaps 4%, if climate warming is minimal. This work should help future growers develop optimum management strategies and, of course, should ultimately benefit all future food consumers.

Technical Abstract: Increased ambient carbon dioxide has been associated with high CO2-induced stomatal closure and affects growth and evapotranspiration of crop canopies. This results in changes of the energy balance components of the soil-plant-atmosphere-system. The agroecosystem wheat model DEMETER was linked to a Soil-Vegetation- Atmosphere-Transfer module which includes the energy balance of the crop canopy and the energy balance of the soil surface. Thus, it is possible to calculate evapotranspiration, canopy temperature and the changed ratio of sensible and latent heat fluxes in response to elevated atmospheric CO2 concentrations. The Free-Air Carbon Dioxide Enrichment (FACE) technique provides a largely undisturbed regime for atmospheric exchange. During the FACE wheat experiment at Maricopa in 1992/93, the effects of elevated atmospheric CO2 concentrations on energy balance and evapotranspiration of the wheat canopy at about 350 ... 370 micro mol/mol (CONTROL) and 550 micro mol/mol (FACE) were investigated. The recorded data were used for model validation. Diurnal trends of all energy balance components and the canopy temperature were simulated for FACE and CONTROL conditions using hourly weather data. Results were compared with the observed data on 16 March 1993. Simulated cumulative seasonal evapotranspiration was found in good accordance to the observed one. The simulations agree with the observation that there is no significant effect of CO2 enrichment on evapotranspiration but there is an increase in water use efficiency of the crop.