The effect of individual and combined drought and heat stress under elevated CO2 on physiological responses in spring wheat genotypes

Abiotic stress due to climate change with continuous rise of atmospheric CO2 concentration is predicted to cause severe changes to crop productivity. Thus, research into wheat cultivars, capable of maintaining yield under limiting conditions is necessary. The aim of this study was to investigate the physiological responses of spring wheat to individual and combined drought- and heat events and their interaction with CO2 concentration. Two heat sensitive (LM19, KU10) and two heat tolerant (LM62, GN5) genotypes were selected and grown under ambient (400 ppm, aCO2) and elevated (800 ppm, eCO2) CO2 concentrations. At the tillering stage, the wheat plants were subjected to different treatments: control, progressive drought, heat and combined drought and heat stress. Our results showed that eCO2 mitigated the negative impact of the moderate stress in all genotypes. However, no distinctive responses were observed in some of the measured parameters between heat sensitive and tolerant genotypes. All genotypes grown at eCO2 had significantly higher net photosynthetic rates and maintained maximum quantum efficiency of PSII photochemistry under heat and combined stress compared to aCO2. Under heat and combined stress, the chlorophyll a:b ratios decreased only in heat tolerant genotypes at eCO2 compared to the control. Furthermore, the heat tolerant genotypes grown at eCO2 showed an increased glucose and fructose contents and a decreased sucrose content under combined stress compared to aCO2. These findings provide new insights into the underlying mechanisms of different genotypic responses to combined abiotic stresses at eCO2 that differ from the response to individual stresses.