Ethylenediurea offers moderate protection against ozone-induced rice yield loss under high ozone pollution.

Tropospheric ozone (O3) is the main phytotoxic air pollutant threatening food security, while ethylenediurea (EDU) can effectively mitigate O3-induced crop yield loss. EDU's mode of action, however, remains unclear, and the underlying physiological mechanisms of mitigating O3-induced crop yield loss are poorly understood. We cultivated hybrid rice seedlings under two O3 treatments (NF, nonfiltered ambient air; and NF60, ambient air plus 60 ppb O3) and sprayed foliage with 0 or 450 ppm EDU every ten days and determine photosynthesis-related traits, biomass indicators, and yield components. We found that EDU significantly increased the leaf nitrogen (N) allocation to photosynthesis (NP) and the grain N accumulation, while the grain N accumulation was positively correlated with NP and root biomass. EDU significantly increased the rice yield mainly by increasing the individual grain weight rather than the number of panicles and grains. While EDU protected from yield loss, the degree of protection was only 31% under NF60 treatment, thus EDU was unable to offer complete protection under high O3 pollution. These results will be conducive to a better understanding of the EDU protection mechanism and better application of EDU under high O3 pollution in the future.