Developing Hyperspectral Indices for Assessing Seasonal Variations in the Ratio of Chlorophyll to Carotenoid in Deciduous Forests

Guangman Song,Quan Wang

doi:10.3390/rs14061324

Abstract

Leaf pigments are sensitive to various stress conditions and senescent stages. Variation in the ratio of chlorophyll to carotenoid content provides valuable insights into the understanding of the physiological and phenological status of plants in deciduous forests. While the use of spectral indices to assess this ratio has been attempted previously, almost all indices were derived indirectly from those developed for chlorophyll and carotenoid contents. Furthermore, there has been little focus on the seasonal dynamics of the ratio, which is a good proxy for leaf senescence, resulting in only a few studies ever being carried out on tracing the ratio over an entire growing season by using spectral indices. In this study, we developed a novel hyperspectral index for tracing seasonal variations of the ratio in deciduous forests, based on a composite dataset of two field measurement datasets from Japan and one publicly available dataset (Angers). Various spectral transformations were employed during this process in order to identify the most robust hyperspectral index. The results show that the wavelength difference (D) type index, using wavelengths of 540 and 1396 nm (calculated from the transformed spectra that were preprocessed by the combination of extended multiplicative scatter correction (EMSC) and first-order derivative), exhibited the highest accuracy for the estimation of the chlorophyll/carotenoid ratio (R2 = 0.57, RPD = 1.52). Further evaluation revealed that the index maintained a good performance at different seasonal stages and can be considered a useful proxy for the ratio in deciduous species. These findings provide a basis for the usage of hyperspectral information in the assessment of vegetation functions. Although promising, extensive evaluations of the proposed index are still required for other functional types of plants.

Highlights

A number of previous studies have indicated that knowledge of the proportion of the leaf chlorophyll and carotenoid content can be more beneficial than the amount of individual pigments in determining plants’ physiological status, since it has become a good indicator for evaluating plant senescence and stress [10–12]
The ratio of chlorophyll to carotenoid content varies for different environments [17–20], with light conditions, which have been extensively demonstrated in different species [21–24]
This study demonstrates the ability of spectral indices to remotely detect the ratio of chlorophyll to carotenoid with seasonal changes in deciduous forests

Summary

Introduction

Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan; Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan. Variation in the ratio of chlorophyll to carotenoid content provides valuable insights into the understanding of the physiological and phenological status of plants in deciduous forests. Further evaluation revealed that the index maintained a good performance at different seasonal stages and can be considered a useful proxy for the ratio in deciduous species. These findings provide a basis for the usage of hyperspectral information in the assessment of vegetation functions. A number of previous studies have indicated that knowledge of the proportion of the leaf chlorophyll and carotenoid content can be more beneficial than the amount of individual pigments in determining plants’ physiological status, since it has become a good indicator for evaluating plant senescence and stress [10–12]. The chlorophyll/carotenoid ratio in leaves with high light published maps and institutional affiliations

Objectives

Methods

Results

Discussion

Conclusion