Faculty of Agriculture, Food & Environment, The Hebrew University, HaMerkaz, Israel
Abstract: 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. 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 ppm) and elevated (eCO2 ∼550 ppm) [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 (ΔTleaf-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 ΔTleaf-air under future conditions.
Our results show that eCO2 boosted the booting stage of the late-maturing genotype (cv. Ruta), thereby prolonging its booting-to-anthesis period by 3 days under drought (p < 0.05). 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 higher 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. ΔTleaf-air was more strongly affected by [CO2]. For a similar LE change of 350 W m–2, ΔTleaf-air changed by ∼3.5°C under eCO2 while it changed by more than 10°C under aCO2. PRI, RUE, ΔTleaf-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.
