Severe ozone pollution drives physiological stress in winter wheat: Evidence from satellite-based chlorophyll...

Understanding the impact of ozone (O₃) pollution on photosynthesis is essential for estimating crop yields and ensuring food security. While remote sensing of Sun-induced chlorophyll fluorescence (SIF) effectively assesses plant stress, most studies have focused on temperature and water deficits, with limited attention to O₃-induced chlorophyll degradation. To address this gap, we utilized the SIF data from the TROPOspheric Monitoring Instrument (TROPOMI) to investigate the response of winter wheat to severe O₃ stress in China's primary wheat-producing region during 2019-2023, a period marked by substantial O₃ pollution. Our analysis revealed that variations in satellite-derived SIF were largely driven by crop structural traits; however, the physiological signal captured by SIF yield (Φ_F) also accounted for 23 % of the observed SIF variability. Notably, using the partial correlation analysis, Φ_F exhibited a stronger sensitivity to O₃ exposure (r = -0.36, as indicated by the maximum daily 8-hour average O₃ concentration [MDA8]) compared to other traditionally influential factors such as maximum daily air temperature (T_max, r = -0.12) and vapor pressure deficit (VPD, r = -0.06). Furthermore, model simulations demonstrated that Φ_F begins to decline sharply when the MDA8 threshold exceeds 132 µg/m³. These findings deepen our understanding of satellite-based SIF observations and underscore the critical importance of monitoring O₃ pollution, an often-overlooked factor, in the context of crop growth and productivity under changing climatic conditions.