Rice is arguably the most important food source on the planet and is consumed by over half of the world's population. Considerable increases in yield are required over this century to continue feeding the world's growing population. This meta-analysis synthesizes the research to date on rice responses to two elements of global change, rising atmospheric carbon dioxide concentration ([CO2]) and rising tropospheric ozone concentration ([O3]). On an average, elevated [CO2] (627 ppm) increased rice yields by 23%. Modest increases in grain mass and larger increases in panicle and grain number contributed to this response. The response of rice to elevated [CO2] varied with fumigation technique. The more closely the fumigation conditions mimicked field conditions, the smaller was the stimulation of yield by elevated [CO2]. Free air concentration enrichment (FACE) experiments showed only a 12% increase in rice yield. The rise in atmospheric [CO2] will be accompanied by increases in tropospheric O3 and temperature. When compared with rice grown in charcoal-filtered air, rice exposed to 62 ppb O3 showed a 14% decrease in yield. Many determinants of yield, including photosynthesis, biomass, leaf area index, grain number and grain mass, were reduced by elevated [O3]. While there have been too few studies of the interaction of CO2 and O3 for meta-analysis, the interaction of temperature and CO2 has been studied more widely. Elevated temperature treatments negated any enhancement in rice yield at elevated [CO2], which suggests that identifying high temperature tolerant germplasm will be key to realizing yield benefits in the future.
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