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• O 3 pollution is a hidden threat to oilseed rape cultivation and processing. • O 3 reduces yield by 20% in spring and 40% in winter oilseed rape cultivars. • O 3 decreases seed quality of the spring, but not the winter, cultivar. • O 3 decreases on-farm quality premiums and profit margins. • Variation in cultivar tolerance may offer agronomists ways to mitigate O 3 impacts. Oilseed rape (Brassica napus L.) is cultivated worldwide, producing 11.5% of global oilseeds at an economic value of 38 billion USD in 2020. It is sensitive to phytotoxic damage from exposure to tropospheric ozone (O 3), a major air pollutant, which disrupts plant physiological processes and thus decreases biomass accumulation. As background ozone concentrations continue to increase globally, we investigated the impact of ozone exposure on seed and oil yield of a shorter-lived spring (cv. Click) and a longer-lived winter (cv. Phoenix) oilseed rape cultivar to ozone levels (treatments with peaks of 30, 55, 80, 110 ppbv) representative of typical European conditions where these cultivars are common. Thousand Seed Weight (TSW), an important measure of final yield, decreased more in Phoenix (40%) than Click (20%) with increasing ozone exposure. Click produced more racemes and many small seeds while Phoenix produced fewer racemes and larger seeds. However, seed quality declined more substantially in Click than Phoenix. The oil content in Click's seed significantly decreased with increased ozone exposure, while less desirable components (moisture, chlorophyll, ash) increased. Scaled to field-level, our findings imply substantial economic penalties for growers, with potential losses of 175–325 USD ha−1 in Click and 500–665 USD ha−1 in Phoenix under ozone concentrations typical of spring and summer periods in Europe. Decreased total yield would likely outweigh the benefits of any improvement in animal oilseed cake quality (increased protein and key micronutrients for livestock feed). Neither cultivar sustained visible injury at earlier growth stages, and Phoenix sustained photosynthesis even under high exposure, thereby making ozone an invisible threat. Our findings of reduced oilseed quantity and quality threaten oilseed rape production, but differences between the cultivars may also offer an opportunity for breeders and agronomists to identify and exploit variation in ozone tolerance in oilseed rape. [Display omitted]. [ABSTRACT FROM AUTHOR]

• Increased temperature improved plant growth and photosynthetic carbon fixation. • O 3 inhibited growth, and Quercus mongolica has a self-repair ability to O 3 stress. • The adverse effects of O 3 on growth and C fixation were mitigated by air warming. • Urban trees show a species-specific difference in plant functional traits. With continuous urbanization and climate warming, increased air temperature and elevated ozone (O 3) concentration often co-occur in many urban areas, but we still lack information about the interactive effects of warming and elevated O 3 on urban trees. In the present experiment, the single and combined effects of increased air temperature (IT, ambient air temperature + 2 °C) and elevated O 3 (EO, ambient air O 3 concentrations + 80 ppb) on carbon (C) fixation and allocation in Quercus mongolica and Pinus tabuliformis, which are widely used as street tree species in urban areas of China, were investigated over two consecutive growing seasons by using 13C isotope techniques. The results showed that IT increased biomass, photosynthetic gas exchange parameters and total 13C content of both tree species. Compared to ambient temperature, IT significantly increased the total 13C content labelled by 56.6 % in Q. mongolica and by 31.2 % in P. tabuliformis in 2021. Elevated O 3 induced a decrease in biomass and net photosynthetic rate (P n) in both tree species. Compared to ambient O 3, elevated O 3 significantly decreased P n by 52.6 % in Q. mongolica and by 37.4 % in P. tabuliformis in 2020. The treatment EO decreased 13C allocation to roots but increased 13C content and distribution in leaves in Q. mongolica. These findings demonstrated that EO inhibited the growth and photosynthesis of the two tree species. Our results showed that Q. mongolica was more sensitive to IT and EO than P. tabuliformis , but the former has a self-repair mechanism under increased O 3 stress as it is able to invest more carbon to repair leaf damage to a certain extent. Our study also found that the total biomass, relative growth rate, P n and total 13C content remained higher under the combination of IT and EO compared to EO alone, suggesting that moderate warming may mitigate the negative effects of elevated O 3 stress to some extent. [ABSTRACT FROM AUTHOR]