Estimating leaf carotenoid contents of shade-grown tea using hyperspectral indices and PROSPECT-D inversion

Quantifying carotenoid contents has many applications in agriculture, ecology, and health science. Hyperspectral reflectance has been one of the promising tools for this purpose. However, previous studies were based on measurements under relatively low light-stress conditions. Therefore, assessing its robustness by using measurements under various levels of stress is required. In this study, the measurements of reflectance and carotenoid contents were carried out with four shading treatments including open-0%, 35%, 75%, and 90% shading to generate various chlorophyll/carotenoid ratios. Then the performances of 15 published hyperspectral indices and PROSPECT-D inversion were evaluated based on our data set for estimating leaf carotenoid contents. According to the ratio of performance to deviation, R-NIR/R-510, R-720/R-521-1, and PROSPECT-D inversion were applicable for this purpose, although calibration of the absorption coefficients was required for PROSPECT-D. Using them, root mean square percentage errors of 4.53-5.46% were achieved. Given that total chlorophyll/carotenoid ratios could be a good indicator for evaluating environmental stress in plants, PROSPECT-D, which also estimates total chlorophyll and anthocyanin contents, could be a strong tool for controlling the qualities of shade-grown tea.