A Novel SIF-Based Framework Outperforms Empirical Models in Regional Ozone Stress Assessment for Winter Wheat

Accurate estimation of regional-scale ozone (O 3 ) uptake flux is critical for assessing crop stress. Traditional Jarvis-type empirical models are limited in capturing canopy conductance dynamics governed by both environmental conditions and plant physiology. Focusing on the winter wheat region of the North China Plain (NCP), this study integrated sun-induced chlorophyll fluorescence (SIF) data from Sentinel-5P/TROPOMI into a photosynthesis model to retrieve canopy conductance ( G c _SIF) and dynamically estimate a SIF-based O 3 uptake flux (POD 0 _SIF) during a 75-d window centered on flowering (44 d before to 30 d after). Jarvis-model-based POD 0 (POD 0 _Jarvis) and AOT40 (accumulated exposure over a threshold of 40 parts per billion) were also calculated for comparison. The results showed good agreement between G c _SIF and eddy covariance-based canopy conductance estimates ( G c _EC) at the site scale, with R 2 values of 0.59 to 0.67 and 0.41 to 0.46 at the daily and hourly scales, respectively. G c _SIF exhibited stronger spatiotemporal consistency with gross primary production than Jarvis-based stomatal conductance ( g s _Jarvis). Spatially, high AOT40 levels were concentrated in the central and northern NCP, while high POD 0 _SIF and POD 0 _Jarvis occurred in the central and southern regions. POD 0 _SIF exhibited greater spatial heterogeneity than POD 0 _Jarvis, with coefficients of variation of 22.62% and 7.50%, respectively, and their difference (ΔPOD 0 ) peaking in the western and northern NCP. Vapor pressure deficit (VPD) contributed 32.3% to ΔPOD 0 , indicating that the Jarvis model inadequately captures the nonlinear stomatal response to varying atmospheric moisture conditions. The POD 0 _SIF framework provides a physiologically constrained approach for regional-scale O 3 stress assessment during critical growth stages of winter wheat.