Ethylenediurea applied during grain filling alleviates physiological damages without yield recovery in wheat under...

Tropospheric ozone (O₃) threatens crop growth and yield, particularly in China, necessitating the urgent exploration and optimization of effective mitigation strategies. Ethylenediurea (EDU) has been widely utilized as a common exogenous chemical protectant against O₃ stress, while its specific mechanism of action remains unclear. In this study, wheat cultivar Lianmai 7 was subjected to ambient O₃ and elevated O₃ (1.5 × ambient) in an O₃ free-air concentration enrichment (O₃-FACE) system and sprayed with either water or 450 μmol/mol EDU exclusively during grain filling, at the interval of 7-10 days. EDU provided partial mitigation for photosynthetic impairment induced by O₃ exposure and effectively improved the antioxidant defense capacity, by enhancing leaf ascorbic acid (AsA) contents, and altering antioxidant enzymes response patterns. Water-treated plants primarily relied on enhancing ascorbate peroxidase (APX) activities to mitigate O₃ stress, while EDU-treated plants tended to maintain peroxidase (POD) and superoxide dismutase (SOD) activities. EDU-mediated protection became progressively insufficient to counteract cumulative O₃ damage between 3 and 7 days post-application during mid-grain filling, as evidenced by attenuated correlations between physiological traits. EDU significantly improved transport and deposit of carbon assimilates from vegetative organs into grains under elevated O₃ as indicated by harvest index, though non-significantly increasing grain yield under elevated O₃. These results suggested that optimizing frequency of EDU application during critical growth stages is essential to improve its protective efficacy under elevated O₃, particularly for the O₃-sensitive cultivars. This study contributes to elucidating the EDU protection mechanism and informing its optimized application in high-O₃ scenarios.