Rice yield enhancement by elevated CO 2 is reduced in cool weather

Abstract

The projected increase of atmospheric CO 2 concentration ([CO 2 ]) is expected to increase rice yield, but little is known of the effects of [CO 2 ] at low temperature, which is the major constraint to growing rice in cool climates. We grew rice under two levels of [CO 2 ] (ambient and elevated by 200 μmol mol −1 ) and two nitrogen (N) fertilization regimes in northern Japan in 2003 (cool weather) and 2004 (warm weather) in the field in a free‐air CO 2 enrichment (FACE) system. Elevated [CO 2 ] significantly increased grain yield in both years in both N regimes, but the magnitude of the increase differed between years: 6% in 2003 vs. 17% in 2004, with a significant interaction between [CO 2 ] and year. This difference resulted from responses of spikelet number and ripening percentage to elevated [CO 2 ]. Enhancement of dry matter production and N uptake at heading by elevated [CO 2 ] was smaller in 2003 than in 2004, although at maturity there was no difference between years. No significant interaction between N regime and [CO 2 ] was detected in yield and yield components. The results suggest that yield gain due to elevated [CO 2 ] can be reduced by low temperature.

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