Investigating the Effect of Elevated Tropospheric Ozone Concentrations on Grain Yield and Nitrogen Use Efficiency of Tropical Rice (Oryza Sativa L.): Evidence from Path Modelling

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Tropospheric ozone (O3), an emerging climate change-induced stressor, enters leaf tissues via stomata, triggering reactive oxygen species (ROS) generation and suppressing key N assimilation enzymes like nitrate reductase and glutamine synthetase impairing nitrogen metabolism and reducing grain yield and nitrogen use efficiency (NUE) in rice. This study evaluated the impact of elevated O3 (e[O3]) on nitrogen (N) uptake, NUE components, and yield attributes across two contrasting seasons using Open Top Chambers (OTCs) with four treatments: UC (ambient, open field, 30 ± 5 ppb), CC (ambient, OTC, 30 ± 5 ppb), EO40 (40 ± 5 ppb), and EO60 (60 ± 5 ppb), across three N levels. Partial Least Squares Path Modeling (PLS-PM) was used to analyze trait interrelationships affecting grain yield. Results showed that e[O3] significantly reduced total N uptake (17–28%), agronomic NUE (27–35%), N recovery efficiency (22–28%), physiological NUE (6–10%), and partial factor productivity of N (14–23%) compared to CC. Grain yield declined by 14–23%, with greater reductions observed during Kharif season, likely due to higher stomatal conductance facilitating increased O3 uptake. Higher N application only partially mitigated O3-induced NUE impairment. PLS-PM identified spikelet fertility as the strongest direct yield determinant under O3 stress.