Sunflower physiological adjustments to elevated CO2 and temperature do not improve reproductive performance and productivity

High levels of carbon dioxide (eCO2) and temperature (eT) affect the physiological performance of sunflowers, but the full extent of their influence on productivity and floral traits remains to be disclosed. Here, we show that eT increased the maximum rate of carboxylation, maximum electron transport capacity, and net rate of triose-phosphate production, indicating enhanced carbon fixation. Although eT increased reactive oxygen species (ROS) concentration in the leaves, no signs of lipid peroxidation in cellular membranes were detected, and plants activated antioxidant systems to counteract the increase in ROS. Moreover, under eT, sunflower pollen exhibited higher amounts of Fe and Zn but also experienced reduced development and productivity due to increased production of empty seeds. In response to eCO2, sunflowers reduced stomatal conductance, limiting water loss, contributing to increased water use efficiency and enhanced photosynthesis. Additionally, under eCO2, sunflowers displayed pollen with higher levels of P, increased biomass gain, and productivity. Lastly, the isolated effects of eCO2 and eT had contrasting impacts on inflorescence size, but the combination of these factors did not result in changes compared to current conditions. However, both factors contributed to increased carotenoid content in ray florets. In contrast, the eCO2eT combination enhanced photosynthesis, flavonoid production in ray florets, and reduced the amount of K and Cu in pollen. In conclusion, eCO2eT improved the physiological performance of sunflowers, but this was not accompanied by increased growth and productivity. The reduction in seed production in sunflowers can have negative impacts on ecology, genetic diversity, and agricultural economy. While eCO2eT did not affect sunflower inflorescence size, they did affect petal pigmentation and pollen quality, which can have significant implications for pollinator health. Understanding the full extent of eCO2eT effects poses a challenge for developing effective mitigation strategies and optimizing agricultural sustainability in the face of climate change.