Assessing the effects of early and timely sowing on wheat cultivar HD 2967 under current and future tropospheric ozone scenarios

This study investigates the impact of elevated ozone (eO 3 ) levels on the growth and yield of the wheat cultivar HD 2967 under different sowing dates in open-top chambers. Wheat was sown early on November 1st and timely on November 20th, 2017, under ambient and elevated O 3 (ambient + 20 ppb), resulting in four treatment groups: AT (ambient + timely), ET (elevated + timely), AE (ambient + early), and EE (elevated + early). Results showed significant reductions in morphological traits and gas-exchange parameters, including photosynthetic rate, stomatal conductance , and water use efficiency under eO 3 . The most notable decreases were observed 40 days after germination (DAG) compared to 80 DAG. Interestingly, while a higher percentage reduction was observed under ET at 80 DAG, a reversal in the trend of percentage reduction between the two stages was noted, suggesting a dynamic response of the wheat cultivar to stress across the growth stage. However, compared with ET's results, early sowing mitigated these negative effects under a futuristic O 3 level scenario, showing no significant impact on grain yield and productivity factors. This resilience is attributed to the extended growth period, enhancing photosynthesis and biomass accumulation while avoiding high eO 3 concentrations during critical reproductive stages. Furthermore, a trade-off in ET plants suggests resources are allocated towards defense (enzymatic and non-enzymatic antioxidants) at the expense of growth, while EE conditions favor growth at later stages, maintaining reproductive fitness despite eO 3 levels. Under conventional timely sowing, wheat may suffer yield declines of up to 30 % amidst rising eO 3 levels. Early sowing emerges as a proactive strategy to maintain wheat productivity under increasing O 3 stress. Future studies should explore the effectiveness of early sowing across multiple wheat cultivars and climatic conditions to inform sustainable agricultural practices in high O 3 areas. Diagram illustrating the implications of adjusting crop sowing dates. The upper part depicts the conventional sowing practice under ambient O 3 condition. The lower part of the picture demonstrates the shift to early sowing dates by 20 days to circumvent peak O 3 levels during critical growth phases. Early sowing enables plants to complete their reproductive cycle before O 3 levels peak, potentially mitigating significant yield losses and other negative impacts observed under ET. • Early sowing mitigates adverse effects of eO 3 on wheat biomass and photosynthesis. • Extended growth period under early sowing compensates for grain yield loss despite increased O 3 . • Conventional timely sowing risks significant wheat yield decline under projected higher O 3 levels. • Trade-off observed between growth and defense mechanisms under timely sowing and eO 3 conditions. • Early sowing can be akey strategy to safeguard wheat productivity in the IGP region against escalating O 3 concentrations.