Carbon dioxide responsiveness mitigates rice yield loss under high night temperature.

Increasing night-time temperatures are a major threat to sustaining global rice (Oryza sativa L.) production. A simultaneous increase in [CO2] will lead to an inevitable interaction between elevated [CO2] (e[CO2]) and high night temperature (HNT) under current and future climates. Here, we conducted field experiments to identify [CO2] responsiveness from a diverse indica panel comprising 194 genotypes under different planting geometries in 2016. Twenty-three different genotypes were tested under different planting geometries and e[CO2] using a Free Air CO2 Enrichment (FACE) facility in 2017. The most promising genotypes and positive and negative controls were tested under HNT and e[CO2]+HNT in 2018. [CO2] responsiveness, measured as a composite response index on different yield components, grain yield, and photosynthesis, revealed a strong relationship (R2=0.71) between low planting density and e[CO2]. The most promising genotypes revealed significantly lower (P < 0.001) impact of HNT in high [CO2] responsive genotypes compared to the least [CO2] responsive genotype. [CO2] responsiveness was the major driver determining grain yield and related components in high [CO2] responsive genotypes with a negligible yield loss under HNT. A systematic investigation highlighted that active selection and breeding for [CO2] responsiveness can lead to maintained carbon balance and compensate for HNT-induced yield losses in rice and potentially other C3 crops under current and future warmer climates.