Response of rice production to elevated [CO2] and its interaction with rising temperature or nitrogen supply: a meta-analysis

We used meta-analysis to synthesize 125 studies assessing the responses\nof rice production to elevated atmospheric carbon dioxide concentration\n({[}CO2]), and the interaction of elevated {[}CO2] with rising\ntemperature or N supply. Elevated {[}CO2] significantly enhanced rice\nyield by 20 %, despite no significant increase in grain size and\nharvest index at elevated {[}CO2]. Belowground biomass increased at\nelevated {[}CO2] to a larger extent than aboveground biomass. Among the\nJaponica, Indica and Hybrid rice cultivars, Hybrid cultivars generally\nshowed the greatest growth response to elevated {[}CO2]. The maximum\nenhancement of rice yield was observed at 600-699 ppm {[}CO2] with less\nbenefit in studies with lower or higher elevated {[}CO2] levels. Rice\nyield responses to elevated {[}CO2] were smaller in FACE compared with\nthe other fumigation methods, largely associated with lower\nphotosynthesis. Increases in rice yield at elevated {[}CO2] were\nconstrained by limited N supply. The detrimental effect of rising\ntemperature on spikelet fertility and harvest index were not be fully\ncounteracted by elevated {[}CO2] effects. Together, the results of this\nmeta-analysis suggest that rising {[}CO2] and warming accompanied by low\nN supply are unlikely to stimulate rice production, especially with the\ncurrent trajectory of emissions scenarios.