Effects of Elevated CO₂ and Global Climate Change on Rice Yield in Japan

Abstract

Long-term CO₂ x temperature experiments on rice using Temperature Gradient Chambers (TGCs) revealed that nearly doubled CO₂ concentration in the atmosphere increases crop dry matter production by 24% through the enhancement of radiation conversion efficiency to biomass, but not through the promotion of radiation interception rate. Although temperature gave a negligibly small influence on the CO₂ effect on biomass production, it significantly affected the grain yield through spikelet fertility. High temperatures were most damaging rice spikelets at the moment of their flowering and made them sterile. The temperature (Tmh) at which 50% spikelets are sterile was 38.2°C for a high temperature-tolerant genotype ‘Koshihikari’, and 36.6°C for a sensitive genotype ‘Akihikari’. Those findings from TGC experiments were parametrized and incorporated into rice growth simulation model SIMRIW.

Impact assessments of elevated CO₂ concentration and global climate change on regional rice yield in Japan were made by using SIMRIW under various climate scenarios. The model predicted that a 100 μmol mol⁻¹ increase in CO₂ concentration alone increases rice yield in Japan by 7 – 8%, and that a 2°C temperature rise significantly reduces this CO₂ effect in the most part of Japan. Then, the effects of 2 × CO₂ climates on regional rice yield were predicted for high temperature-sensitive and tolerant genotypes by using 2 × CO₂ climate scenarios generated by GFDL, GISS and UKMO general circulation models. It was found out that the 1.6°C difference in the spikelet sensitivity to high temperature damage between those two genotypes gives significantly large effects on the predicted rice yield in central-south (Tokai and South Kanto districts) and south-western Japan under 2 × CO₂ climates. Even with the high temperature-tolerant genotype, rice yield in those regions was predicted to decrease by 0 – 10% than the present under 2 × CO₂ climates except for GISS, while that in northern Japan was predicted to increase by 10 – 25% depending on climate scenarios. The model also predicted that 2 × CO₂ climates significantly increase yearly yield variability in the central-south and southwestern Japan, while they stabilize the yield fluctuation in the northern Japan. Alternations of phenological development genotypes and cropping seasons furthermore promoted the positive effects of 2 × CO₂ climates in the northern Japan, but did not significantly mitigate the negative effects in the southern Japan. For mitigating the predicted negative effects of 2 × CO₂ climates in the southern Japan, explorations for high temperature-resistant genotypes are necessary.