COS 101-6 - Future impacts of global warming and drought on wheat production and quality in a world with a higher atmospheric CO₂ level

Background/Question/Methods

The combination of a future rise in atmospheric carbon dioxide concentration ([CO₂]), warming, and drought will significantly impact wheat production and quality. Genotype phenology is likely to play an essential role in such an effect. Yet, its response to elevated [CO₂] and drought has not been studied before. We simulated future conditions by conducting temperature-controlled glasshouse [CO₂] enrichment experiments in which two wheat cultivars with differing maturity timings and life cycle lengths were grown under ambient (aCO₂ ∼ 400 μmol mol^–1) and elevated (eCO₂ ∼ 550 μmol mol^–1) [CO₂]. The two cultivars, bred under dry and warm Mediterranean conditions, were well-watered or exposed to drought at 40% pot holding capacity. Leaf latent heat flux (LE) was derived to assess evaporative cooling, and radiation use efficiency (RUE) was calculated from the gas exchange and radiation measurements on several dates along the season. Simultaneous hyperspectral and thermal images were taken to derive the photochemical reflectance index (PRI) and the temperature difference between the leaf and its surrounding (ΔT_leaf-air) at the leaf and canopy levels. We aimed to explore water×[CO₂]×genotype interaction in terms of phenology, physiology, and agronomic trait response and to describe remote sensing-based parameterization of RUE and ΔT_leaf-air under future conditions.

Results/Conclusions

Our results showed that eCO₂ boosted the booting stage of the late-maturing genotype (cv. Ruta), thereby prolonging its booting-to-anthesis period by 3 days (p< 0.05) under drought. The prolonged period resulted in a much higher carbon assimilation rate, particularly during pre-anthesis (+87% for Ruta vs. +22% for the early-maturing genotype of Zahir). Surprisingly, transpiration rate and grain protein content were unaffected by [CO₂] in both cultivars and water treatments. Ruta’s higher photosynthesis rate was not translated into more aboveground biomass or grain yield, whereas both cultivars showed a similar 20% increase under eCO₂ and drought. Overall, Zahir had a more efficient source-to-sink balance with a lower sink limitation than Ruta. There was a decoupling in the PRI-RUE relationship under drought at aCO₂, but the relationship remained strong at eCO₂. ΔT_leaf-air was more strongly affected by [CO₂]. For a similar LE change of 350 W m^–2, ΔT_leaf-air changed by ∼3.5°C under eCO₂ while it changed by more than 10°C under aCO₂. PRI, RUE, ΔT_leaf-air, and LE decreased linearly with canopy depth, displaying a single model throughout the canopy layers. The complex water×[CO₂]×genotype interaction in this study implies that future projections should account for multifactor interactive effects.