Development of Novel Sun-Induced Chlorophyll Fluorescence Spectral Indices for Assessing Leaf Chlorophyll and Carotenoid Contents in Rice

Abstract. Monitoring the in-situ photosynthetic pigments content in crop leaves is of great significance for the study of the interaction mechanism between plants and the environment. Numerous reflectance spectral indices have been developed for estimating pigments. However, in most cases, the estimation accuracy decreased when employing the indices for individual growth stages or single cultivars. In this study, we aim to develop fluorescence spectral indices for estimating photosynthetic pigments which are insensitive to cultivars and growth stages. We used leaf sun-induced chlorophyll fluorescence and developed four types of spectral indices: fluorescence difference index (FDI), fluorescence ratio index (FRI), normalized fluorescence difference index (NFDI), three-band sum ratio index (TBSR). Each index considers upward and downward situations, and compared our results with the published reflectance indices and some multivariate models. We obtained the indices by using “lambda-by-lambda” band-optimization (LLBO) algorithm and acquired the target indices using statistical methods. Results showed that each fluorescence index except FDI is better than the published reflectance indices. This advantage will be more obvious when there are many cultivars. Under evaluation of chlorophyll content, the FRI type index‘s coefficient of determination (R2) of more than 70% of the cultivars is better than the published reflectance indices. Meanwhile, in the evaluation of carotenoids content, the fluorescence indices can effectively avoid the emergence of extreme situations. This study showed that fluorescence indices can eliminate the influence of different cultivars on photosynthetic pigments to a certain extent, but it was not significant when it extended to different growth stages.