Yield responses of southern US rice cultivars to CO2 and temperature

Previous studies on the effects and interactions of atmospheric carbon dioxide concentration ([CO2]) and air temperatures have shown large differences in growth and yield responses among Asian rice (Oryza sativa L.) cultivars. Far less attention has been focused on rice cultivars commonly grown in the Southern US. This 2-year study was conducted to determine the effects of [CO2] and air temperature 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 mol mol−1. In 2000, an additional chamber containing all three cultivars was maintained at 28 ◦C and an ambient [CO2] treatment of 350 mol mol−1. In 2002, a more detailed study examining both main crop (MC) and ratoon crop (RC) 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 mol mol−1. In 2002, an additional chamber was maintained at 27/23 ◦C and an ambient [CO2] treatment of 350 mol mol−1. 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 46–71% 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 MC but more than doubled RC yields. 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]. Published by Elsevier B.V.