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Selecting Crop Cultivars to Capitalize on Rising Atmospheric CO2 Concentrations
Baker, J.T. 2004. Yield responses of southern US rice cultivars to CO2 and temperature. Agricultural and Forest Meteorology 122: 129-137.

The author reports there is "considerable variability among current rice cultivars in their responses to CO2 and temperature (Ziska and Teramura, 1992; Ziska et al., 1996; Moya et al., 1998) leading to the possibility [and, we would add, profitability] of selecting rice cultivars against these two environmental variables for yield increases and/or stability in a possibly warmer, but almost certainly higher future CO2 world."

What was done
In the first year of a two-year study, Baker grew Southern United States rice cultivars Cocodrie, Jefferson and Cypress for an entire season in outdoor, naturally-sunlit, controlled-environment chambers at a constant day/night temperature of 28C at CO2 concentrations of 350 and 700 ppm. In the second year, he grew the cultivar Lamont under the same conditions, but at day/night temperatures of 27/23C, as both a main crop and as a ratoon crop.

What was learned
In the first experiment, grain yield per plant rose by 46%, 57% and 71% in response to the doubling of the air's CO2 content in the Cocodrie, Jefferson and Cypress cultivars, respectively, while in the second experiment with the Lamont cultivar it rose by 12% when the rice was grown as a main crop but by 104% when it was grown as a ratoon crop.

What it means
Baker states that "the wide range in grain yield responsiveness to CO2 enrichment found among these four US rice cultivars points to the potential for selecting or developing high yielding US rice cultivars with the ability to take advantage of expected future global increases in CO2." He also notes that "CO2 enrichment could have potentially large positive effects on ratoon crop yields." By capitalizing on this type of knowledge, we should be able to greatly increase rice productivity and, by analogy, the productivity of many crops in the years and decades to come by appropriate cultivar selections and wise crop breeding strategies.

Moya, T.B., Ziska, L.H., Namuco, O.S. and Olszky, D. 1998. Growth dynamics and genotypic variation in tropical, field-grown paddy rice (Oryza sativa L.) in response to increasing carbon dioxide and temperature. Global Change Biology 4: 645-656.

Ziska, L.H. and Teramura, A.H. 1992. Intraspecific variation in response of rice (Oryza sativa) to increased CO2 - photosynthetic, biomass and reproductive characteristics. Physiologia Plantarum 84: 269-276.

Ziska, L.H., Manalo, P.A. and Ordonez, R.A. 1996. Intraspecific variation in the response of rice (Oryza sativa L.) to increased CO2 and temperature: growth and yield response of 17 cultivars. Journal of Experimental Botany 47: 1353-1359.

Reviewed 2 June 2004