Setting the stage for their study, Roy et al. (2015) write that rice is “one of the most important C₃ species of cereal crops,” adding that it “generally responds favorably to elevated CO₂.” However, they note that the actual response of rice crops to elevated CO₂ and warming “is uncertain.” The team of five Indian scientists set out “to determine the effect of elevated CO₂ and night time temperature on (1) biomass production, (2) grain yield and quality and (3) C [carbon], N [nitrogen] allocations in different parts of the rice crop in tropical dry season.”

The experiment they designed to achieve these objectives was carried out at the ICAR-Central Rice Research Institute in Cuttack, Odisha, India, using open-top-chambers in which rice (cv. Naveen) was grown in either control (ambient CO₂ and ambient temperature), elevated CO₂ (550 ppm, ambient temperature) or elevated CO₂ and raised temperature (550 ppm and +2°C above ambient) conditions for three separate growing seasons.

In discussing their findings, Roy et al. write that the aboveground plant biomass, root biomass, grain yield, leaf area index and net C assimilation rates of the plants growing under elevated CO₂ conditions all showed significant increases (32, 26, 22, 21, and 37 percent, respectively) over their ambient counter-parts. Each of these variables were also enhanced under elevated CO₂ and increased temperature conditions over ambient CO₂ and temperature, though to a slightly lesser degree than under elevated CO₂ conditions alone. 

With respect to grain quality, the authors report there was no difference among the parameters they measured in any of treatments, with the exception of starch and amylose content, which were both significantly higher in the elevated CO₂ and elevated CO₂ plus elevated temperature treatments. The C and N grain yields were also both significantly increased in both of these treatments compared with control conditions.

The results of this study thus bode well for the future of rice production in India during the dry season. As the CO₂ concentration of the air rises, yields will increase.  And if the temperature rises as models project, yields will still increase, though by not quite as much. These findings, coupled with the fact that the grain nutritional quality (as defined by an increase in amylose content) was enhanced by elevated CO₂, suggest there is a bright future in store for rice in a carbon dioxide-enhanced atmosphere.

Reference

Roy, K.S., Bhattacharyya, P., Nayak, A.K., Sharma, S.G. and Uprety, D.C. 2015. Growth and nitrogen allocation of dry season tropical rice as a result of carbon dioxide fertilization and elevated night time temperature. Nutrient Cycling in Agroecosystems 103: 293-309.