Tracking water limitation in photosynthesis with sun-induced chlorophyll fluorescence

Sun-induced chlorophyll fluorescence (SIF) has an inherent link to photosynthesis. It is therefore very sensitive to subtle, stress-induced changes in photosynthetic activity. This study shows the evolution of the SIF emission of a yellow mustard stand grown in plant boxes under varying water supply and under varying meteorological conditions, causing changes in the evaporative demand. Affected by both plant physiological processes and by changes in the plant canopy structure, we combined the fluorescence measurements at different wavelengths with reflectance measurements to assess the effect of both components. Using the Fluorescence Correction Vegetation Index, we are able to separate the contribution of the vegetation structure and the plant physiology to the SIF signal. A decrease in water availability causes an instantaneous drop in the SIF emission at 760 nm (SIFA). This decrease is not shown in the SIF emission at 687 nm (SIFB). Because of the difference in behavior between the SIF emission at the two bands, their ratio is a promising metric for detecting a stress-induced reduction in photosynthetic activity. Soon after the decrease in SIFA, we notice structural changes in the canopy architecture. These structural changes cause additional changes in the SIFA emission. Due to the increase in the non-photochemical quenching component, the decrease in SIFA emission is associated with a decrease in the photochemical reflectance index (PRI). This presentation illustrates the relative importance of each process at every step of the plant’s reaction to drought stress by means of field data collected over a mustard canopy