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Title: FREE-AIR CO2 ENRICHMENT EFFECTS ON WHEAT AND SORGHUM AT MARICOPA, ARIZONA, USA

Author
item MATTHIAS, ALLAN - UNIV OF ARIZONA TUCSON AZ
item LEAVITT, STEVEN - UNIV OF ARIZONA TUCSON AZ
item THOMPSON, THOMAS - UNIV OF ARIZONA TUCSON AZ
item Kimball, Bruce
item Pinter Jr, Paul
item Wall, Gerard - Gary
item RAUSCHKOLB, ROY - UNIV OF ARIZONA TUCSON AZ
item OTTMAN, MICHAEL - UNIV OF ARIZONA TUCSON AZ
item ROTH, ROY - UNIV OF ARIZONA TUCSON AZ
item BROOKS, TALBOT - UNIV OF ARIZONA TUCSON AZ

Submitted to: International Symposium on Carbon Dioxide and Vegetation Advanced Internati
Publication Type: Proceedings
Publication Acceptance Date: 3/19/2001
Publication Date: 7/15/2001
Citation: Matthias, A.D., Leavitt, S.W., Thompson, T.L., Kimball, B.A., Pinter Jr, P.J., Wall, G.W., Rauschkolb, R.S., Ottman, M.J., Roth, R.L., Brooks, T.J. 2001. Free-air co2 enrichment effects on wheat and sorghum at maricopa, arizona, usa. International Symposium on Carbon Dioxide and Vegetation Advanced Internati. pp. 87-96.

Interpretive Summary: In order to determine the consequences of present and future global environmental changes on the security of world food and fiber production, efforts are underway to determine the growth and other physiological responses of major crops to changing environmental factors. These global changes especially include the increasing concentration of atmospheric carbon dioxide (CO2), which is expected to double sometime during the next century. We have determined the yield, growth and physiological responses of cotton, wheat, and sorghum growing under open-field conditions to elevated concentrations of CO2 like those expected near the middle of the next century. Briefly, cotton growth showed substantial increases (40%). Wheat yield increases were more modest, about 15% at ample water and fertilizer but more under drought and less under low fertility. Preliminary sorghum yields showed little response at ample water but about a 13% increase in yield under drought. Eventually, this work should led to optimum management strategies for future crop production and, of course, should ultimately benefit all future food and fiber consumers.

Technical Abstract: Atmospheric CO2 concentration is expected to increase from the current level of about 360 ppm to about 500 ppm by the end of the 21st century. Free-air carbon dioxide enrichment (FACE) technology is being used at several locations throughout the world to improve our understanding of how increasing CO2 may impact natural and agroecosystems in the coming century. In Arizona, the technology has been used at the University of Arizona Maricopa Agricultural Center to study FACE effects on cotton (1989-1991) and spring wheat (1992-1997), both important C3 species. Our current two-year study (1998-1999) at Maricopa is focused on sorghum, an important C4 species. Briefly, yield results from the FACE wheat experiments suggest that with ample water, wheat grain yields are likely to increase about 15% for an increase in atmospheric CO2 levels to 200 umol mol-1 above current ambient levels, whereas under water stress we found the yield stimulation due to elevated CO2 to be about 22%. When grown under low soil nitrogen conditions characteristic of agriculture in many developing nations, CO2 increased yield by 8%. For sorghum, preliminary results from the 1998 growing season (July- December) indicate that a +200 umol mol-1 CO2 enrichment has little effect on grain yield when plants are well supplied with water. Under limited irrigation, sorghum yields were stimulated by 17%. In addition to grain yield and carbon accumulation results, findings are presented concerning the effects of FACE on canopy temperature, reflectance, PAR absorptance, energy budget, evapotranspiration, root development, soil CO2 and N2O fluxes, and changes in soil C from soil and plant C isotope analysis.