Single versus recurrent heat stress: A case study on the impact of a stress at flowering on the sorghum response to a subsequent post-flowering stress

Abstract

The increasing intensity and frequency of heat waves due to climate change pose a growing threat to global food security. Two experiments were conducted under controlled conditions using six temperature scenarios to compare the effects of single and recurrent heat stresses on maximum photosystem II quantum efficiency (F_v/F_m), above-ground plant biomass, grain yield and grain yield components in two sorghum genotypes. This study confirmed that the responses of grain number and thousand grain weight are highly dependent on stage development for both single and recurrent heat stresses. Recurrent heat stresses have synergistic effects, leading to around 20 % more yield losses than the cumulative responses to the corresponding single stresses. In contrast, F_v/F_m was less reduced by heat stress if the plants had been subjected to a previous stress. The large reduction in thousand grain weight under recurrent heat stresses may result in a strong remobilization of carbohydrates to sinks other than the main stem panicle. The increased tillering induced by single heat stresses and further amplified under recurrent heat stresses could partly explain this effect. The study highlights the complexity of plant responses to heat stress and the challenges of predicting outcomes under recurrent stress conditions.