Elevated CO2 and heat stress interactions affect grain yield, quality and mineral nutrient composition in rice under field conditions

Heat stress is a major constrain to sustain rice production and grain quality. Rising atmospheric [CO2] is predicted to increase photosynthesis resulting in higher biomass and yield. Conversely, both elevated (e[CO2]) and heat stress (HT) are documented to deteriorate grain quality traits in rice. However, interactive effect of e[CO2] + HT on rice grain yield, quality traits and particularly mineral composition under natural field condition in tropical environments are limited. Independent field experiments were conducted to assess the potential impact of e[CO2] alone and in combination with HT on grain yield, quality traits and mineral composition of two rice cultivars Nerica-L-44 (heat tolerant) and Indian basmati rice variety Pusa 1121, using field based open top chamber (OTC) facility. Elevated [CO2] significantly influenced grain quality traits by increasing chalkiness (69-83%), amylose content (18-37%), decreasing protein content by 4% and altering grain mineral nutrient composition across the cultivars. Proportion of chalky grains was further increased in Nerica-L-44 and Pusa 1121 under e[CO2] + HT interaction. Correlation analysis revealed negative relationship of grain minerals with chalkiness and amylose content. In summary, independent exposure of rice to e[CO2] reduced grain quality and e[CO2] + HT further increased the negative effects on grain nutrient and quality.