Panicle temperature explains contrasting yield responses of rice genotypes to elevated CO2 and increased temperature in T-FACE environments

Abstract Elevated CO2 increases, while high temperature decreases, rice yield. We hypothesize, the interplay between these opposite effects vary across genotypes and these variations are associated with abilities of genotypes in avoiding and tolerating stress. We evaluated Japonica genotype (Changyou5) and Indica genotype (Yangdao6) under combinations of two CO2-levels (ambient and enriched to 590 μmol mol−1) and two canopy temperatures (ambient and warmed by 2.0 ºC) in Temperature-by-Free-Air-CO2-Enrichment systems over two seasons. The elevated-CO2 fully offset the adverse effects of the elevated-temperature on grain yield of Yangdao6 but failed to do so for Changyou5. Yangdao6 increased yield by 20.0%, while Changyou5 decreased it by 7.8% under the combined elevated-CO2 and elevated-temperature. This genotypic difference was partly due to higher leaf-nitrogen content of cv. Yangdao6, resulting in superior light conversion efficiency. However, it was more explained by a comparatively smaller decrease in spikelet fertility (thus, harvest index) in Yangdao6, mainly resulting from lower panicle temperature during flowering. The lower panicle temperature in Yangdao6 was due to earlier flowering hours as well as to higher panicle-nitrogen content that presumably led to more transpirational cooling. The above key genotypic traits could be explored in rice breeding programs to improve yield resilience to climate change.