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Title:   Author  item
                                            Baker, Jeffreyitem
                                            Kim, Soo Hyungitem
                                            Gitz, Dennisitem
                                            Timlin, Dennisitem
                                            Reddy, Vangimalla
  Submitted to: Journal of Agricultural Meteorology of Japan
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/3/2004
                                    Publication  Date: 11/29/2004
                                    Citation: Baker, J.T., Kim, S., Gitz, D.C., Timlin, D.J., Reddy, V. 2004. Photosynthesis and yield of southern us rice cultivars in response to co2 and temperature. Journal of Agricultural Meteorology of Japan. 60(5):457-462.Interpretive Summary: Due to the continued burning of fossil fuels the amount of carbon dioxide in the Earth's atmosphere is rising. Plants grow by using sunlight to fix carbon dioxide in a process called photosynthesis. Rice is the most important world-wide food crop for humans. Experiments were conducted in outdoor growth chambers to study the effects of high levels of atmospheric carbon dioxide on rice growth and yield. We also conducted these experiments across wide ranges of air temperatures to understand the effects of carbon dioxide on rice grain yield at different temperatures.  We conducted these experiments using four rice varieties grown in the United States. We found that high levels of atmospheric carbon dioxide increased rice grain yields by 12 to 71 percent among the rice varieties.  Temperature extremes of 66 F and 95 F resulted in no rice grain yield.  We found that a moderate air temperature of 80 F produced the highest rice grain yield.  These results can be used by plant breeders to develop new rice varieties that will grow and yield better in our future higher carbon dioxide world.
                                Technical Abstract: Previous studies on the effects and interactions of atmospheric CO2 concentration and air temperatures have shown large differences in growth and yield responses among Asian rice cultivars.  Far less attention has been focused on rice cultivars commonly grown in the Southern USA.  This two year study was conducted to determine the effects of CO2 and air temperature treatments on four Southern US rice cultivars.  In 2000 'Cocodrie', 'Cypress' and 'Jefferson' were grown season-long in five outdoor, naturally sunlit, controlled environment chambers in constant day/night air temperature regimes of 24, 28, 32, 36 and 40 C under an elevated CO2 of 700 ppm.  In 2000, an additional chamber containing all three cultivars was maintained at 28'C and an ambient CO2 treatment of 350 ppm. In 2002 a more detailed study examining both main crop and ratoon crop  yields was conducted with the rice cultivar 'Lamont' in these same chambers with day/night air temperature treatments of 19/15, 23/19, 27/23, 31/27 and 35/31 C under an elevated CO2 of 700 ppm. In 2002 an additional chamber was maintained at 27/23 C and an ambient CO2 treatment of 350 ppm.  In the 2000 experiment, all the plants of all three cultivars in the 40 C treatment died during early vegetative growth.  In the constant 36 C air temperature treatment all three cultivars survived to produce panicles but failed to produce any seed yield.  At the 28 C temperature treatment, CO2 enrichment increased grain yield by 46 to 71% among the three cultivars with the cultivar Cypress being the most responsive to CO2 enrichment. In the 2002 experiment with the cultivar Lamont, plants in the 35/31 and 19/15 C treatments survived to produce panicles but failed to produce any seed yield.  In the 27/23 C treatment, CO2 enrichment resulted in a non-significant increase in seed yield for the main crop but more than doubled ratoon crop yields. Examination of the seasonal trends in canopy photosynthesis revealed that this elevated [CO2] induced increase in RC yield was likely the result of faster re-growth and greater light capture as well as higher canopy photosynthetic rates during the ratoon crop grain filling period.  Short-term cross-switching of [CO2] treatments revealed a significant down-regulation of canopy photosynthesis in response to long-term [CO2] enrichment for the rice cultivar Lamont in the 2002 experiment.  Comparisons of these results with findings from prior studies on Asian indica and japonica cultivars indicate that these Southern US rice cultivars may be more sensitive to high temperature stresses during reproductive development than previously studied Asian cultivars. These results also point to the possibility of selecting or breeding rice cultivars with enhanced capability to take advantage of future global increases in CO2.


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