Sensing Plant Physiology and Environmental Stress by Automatically Tracking Fj and Fi Features in PSII Chlorophyll Fluorescence Induction

Following a step excitation, chlorophyll fluorescence (ChlF) from photosystem II of a dark-adapted plant leaf exhibits the well-known OJIP pattern. The OJIP induction has been widely applied in plant science, agriculture engineering, and environmental engineering. While the J and I phases are related to transitions of photochemical reaction redox states, characteristic fluorescence intensities for the two phases (Fj and Fi) are often treated as fixed time points in routine measurement and thus do not account for variations in plant and experimental conditions, which (1) neglects the time differences, potentially useful information for characterizing plant status and environmental factors, and (2) leads to errors in measured Fj and Fi values. In this work, a method for consistent measurement of Fj and Fi was developed through polynomial fitting and curvature analysis. The method measures the curvatures in the OJIP curve and automatically tracks the characteristic transition points under variable sample and experimental conditions. Experiments were carried out to demonstrate the concept and classification capabilities of the developed method. This research established a new framework to analyze ChlF and enhanced the applications of ChlF.