Effects of Elevated CO2 Concentration and High Temperature on the Growth and Development of Rice

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Abstract
The effects of elevated CO2 concentrations and high temperatures on growth and development were investigated in the Japonica rice cultivar ‘Akihikari’ which was grown in two temperature gradient tunnels (TGT) newly developed by the authors. The TGT system provided temperature gradients along the long axis of the tunnel of up to 4°C above the ambient in Kyoto, Japan, while maintaining natural daily and seasonal temperature variations. The daytime CO2 concentration in one tunnel was kept at an ambient level (≈350ppm), and that in the other at 840ppm in 1990 and 690ppm in 1991 during the entire growing season. Three N fertilization levels (0.3, 1.2, 2.4g/pot) were created at each temperature × CO2 treatment in TGT. The elevated CO2 slightly promoted leaf area development at the initial stage, though this effect decreased with growth, resulting in only a small effect at the heading stage. The nearly doubled CO2 concentrations increased the crop dry weight at the intermediate N level by 24% at the heading and 16% upon maturity on average over different temperature conditions. The enhancement rates of the doubled CO2 in the panicle dry weight under outdoor temperature conditions were 15, 30 and 24% at the low, intermediate and the high N applications, respectively. Panicle dry weights under ambient and doubled CO2 both decreased drastically with temperature rises. These results obtained by long-term experiments under field-like conditions suggested that, although elevated CO2 concentrations in the atmosphere promote crop dry matter production, the effects on yield are significantly influenced by temperature and N conditions.

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