Maize hybrids response to limited nitrogen under current and future CO₂ environments

Given the increased nitrogen fertilization, rise in fertilizer prices, and atmospheric CO₂ levels, it is crucial to understand how crops respond to these changing environmental conditions. In this study, using sunlit growth chambers, we investigated the responses of ten maize hybrids to elevated CO₂ (eCO_2, 760 ppm) and low nitrogen (20% of control, LN) conditions during the early seedling stage. The study revealed significant differences (p < 0.5 to p < 0.001) in the measured morpho-physiological parameters among the hybrids under LN, except for root traits. Under eCO₂ and LN conditions, the chlorophyll content and nitrogen balance index reduced by 15% and 39%, respectively, compared to the control. Conversely, the flavonoid and anthocyanin increased by 37% and 25% under eCO₂ and LN, respectively. The LN had a remarkable impact on shoot growth, leading to significant reductions in plant height (28%), leaf area (52%), and shoot dry weight (43%) under eCO₂ compared to control N under ambient CO₂. In contrast, the effect of eCO₂ on shoot growth was not evident, suggesting a cross-over response of C₄ plants to the eCO₂. Under eCO₂ and LN, the plants produced longer roots (8.9%) with a reduced diameter and a high root-to-shoot ratio compared to the control. The percent changes in root length, average diameter, and root-to-shoot ratio under eCO₂ and LN compared to control N and ambient CO₂ were 23%, -8.8%, and 96%, respectively. Among the ten hybrids, the cumulative eCO₂ and LN response index revealed that PGY7215VT2P and Armor-1717 had higher responses compared to D57VP51 and REV-25BHR26, indicating their potential for growing under nitrogen-limited conditions.