Adverse high temperature effects on pollen viability, seed-set, seed yield and harvest index of grain-sorghum [Sorghum bicolor (L.) Moench] are more severe at elevated carbon dioxide due to higher tissue temperatures

Global climate change, especially, increases in carbon dioxide (CO2) concentration and the associated increases in temperature will have significant impact on the crop production. Grain-sorghum [Sorghum bicolor (L.) Moench] cultivar DeKalb 28E was grown at daytime maximum/nighttime minimum temperature regimes of 32/22, 36/26, 40/30 and 44/34 8C at ambient (350 mmol CO2 mol ) and elevated (700 mmol CO2 mol ) CO2 from emergence to maturity in controlled environments to quantify the effects of temperature and CO2 on the reproductive processes and yield. Growth temperatures of 40/30 and 44/34 8C inhibited panicle emergence. Growth temperatures 36/26 8C significantly decreased pollen production, pollen viability, seed-set, seed yield and harvest index when compared to 32/22 8C. Percentage decreases in pollen viability, seed-set, seed yield and harvest index due to elevated temperature were greater at elevated CO2 when compared with ambient CO2. Elevated CO2 increased seed yield (26%) at 32/22 8C, but decreased seed yield (10%) at 36/26 8C. At high temperatures, elevated CO2 increased vegetative growth but not seed yield, thus, leading to decreased harvest index. We conclude that the adverse effects of elevated temperature on reproductive processes and yield of grain-sorghum were more severe at elevated CO2 than at ambient CO2; and the beneficial effects of elevated CO2 decreased with increasing temperature. The adverse temperature sensitivity of reproductive processes and yield at elevated CO2 was attributed to higher canopy foliage and seed temperatures. # 2006 Elsevier B.V. All rights reserved.