Spectroscopic Characterization of Leaf Color for Identifying Riparian Woody Species

This study aims to develop and apply two spectroscopic techniques to characterize leaf color and identify riparian woody species that play a fundamental role in the stability of riverine ecosystems.

First, a handheld spectrophotometer was used to measure the chromatic coordinates in the green color (G) of leaves from five riparian woody species—Salix salviifolia, Populus nigra, Fraxinus angustifolia, Alnus glutinosa, and Prunus avium—located downstream of the "El Pardo" reservoir in Madrid, Spain (near a military base). Measurements were recorded in the CIELAB color space and subsequently converted to RGB for color differentiation analysis, totaling 1.000 chromatic readings. A generalized linear model (GLM) logistic regression was applied to compare green color (G) variations among the species.

Second, UV-vis spectroscopy was employed to quantify total chlorophylls (Chl), the primary pigments responsible for leaf coloration. A total of 605 plant samples were collected, comprising 11 samples per species. UV-vis spectra were measured from 400 to 700 nm using a quartz cuvette with a 1 cm optical path.

Alnus glutinosa showed the highest green reflectance at 98.8%, followed by Salix salviifolia at 92.3%. Regarding chlorophyll a concentration, Alnus glutinosa exhibited the highest levels (10.16 ± 1.69 mg/L), followed by Populus nigra and Fraxinus angustifolia with concentrations of 9.10 ± 0.71 mg/L and 9.18 ± 1.71 mg/L, respectively. Salix salviifolia and Prunus avium had lower chlorophyll a concentrations. To further assess green color (G) data, two chlorophylls' spectra were analyzed using PNOA orthophotos 2006, 2009, 2011, 2014, 2017, 2020, and 2023.

This study enhances our understanding of the relationship between green reflectance and chlorophyll content, providing valuable insights for ecological monitoring and riparian restoration efforts.