Ambient ozone pollution degrades rice grain nutritional quality and straw feed value under field conditions in Bangladesh.

Ambient tropospheric ozone is a pervasive air pollutant and an emerging threat to crop quality, food security, and agroecosystem sustainability. While ozone-induced yield losses are well documented, its impacts on crop nutritional quality and livestock feed value under field conditions remain poorly quantified. We investigated the effects of chronic ambient ozone exposure on nutrient uptake, grain micronutrient composition, and straw feed quality in six genotypes grown under field conditions in Bangladesh, one of the world's most ozone-exposed rice-growing regions. Ethylenediurea was applied to provide a diagnostic contrast for ozone-related responses under ambient field conditions across three consecutive growing seasons. Ambient ozone was associated with reduced plant carbon and nitrogen uptake and lower crop nitrogen-use efficiency in ozone-sensitive genotypes. Grain nutrient uptake declined, accompanied by a reduction in grain iron concentration (≈22%) and smaller declines in zinc, together with increased phytate levels, indicating reduced micronutrient bioavailability. In parallel, straw lignin content increased in sensitive genotypes, reflecting stress-induced carbon allocation to structural defenses and a deterioration in forage quality. Multivariate analyses demonstrated that ozone exposure weakened the association between nutrient-use efficiency and grain nutritional quality. In contrast, the tolerant genotype Kasalath maintained nutrient uptake, use efficiency, and grain micronutrient composition under ozone stress. Our findings demonstrate that field-level ambient ozone pollution is associated with declines plant physiological performance, degrade livestock feed value, and exacerbate human micronutrient risks, highlighting the need for integrated air-quality management and crop adaptation strategies in ozone-affected regions.