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 (eO₃) 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 O₃ (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 eO₃. 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 O₃ 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 eO₃ 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 eO₃ levels. Under conventional timely sowing, wheat may suffer yield declines of up to 30 % amidst rising eO₃ levels. Early sowing emerges as a proactive strategy to maintain wheat productivity under increasing O₃ stress. Future studies should explore the effectiveness of early sowing across multiple wheat cultivars and climatic conditions to inform sustainable agricultural practices in high O₃ areas.