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

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 (ΦF) also accounted for 23 % of the observed SIF variability. Notably, using the partial correlation analysis, ΦF 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 (Tmax, r = -0.12) and vapor pressure deficit (VPD, r = -0.06). Furthermore, model simulations demonstrated that ΦF 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.