Spectral Reflectance Changes Associated with Autumn Senescence of Aesculus hippocastanum L. and Acer platanoides L. Leaves. Spectral Features and Relation to Chlorophyll Estimation

The reflectance spectra of adaxial surfaces of Aesculus hippocastanum L. and Acer platanoides L. leaves in the course of autumn pigment transformation were recorded. A dramatic decrease in and almost complete disappearance of chlorophyll (Chl) gave an opportunity for the investigation of relations between the reflectance changes and the pigment concentrations. The signature analysis of reflectance spectra indicated that in the green to yellow leaves of both species the maximal standard deviation of reflectance coincided with the red absorption maximum of Chla. However, within the leaves with high Chl, minimal sensitivity to pigment variations was observed at 675 nm. The maximal standard deviations were found near 550 to 560 and 700 to 710 nm. The revealed spectral features can serve as sensitive indicators of early stages of leaf senescence. The several functions of reflectance were found to be directly proportional to Chl (a square of correlation coefficient of more than 0.97); that allows an assessment of the pigment concentration ranging from 0.5 to 27.5 nmol/cm² with an estimation error of less than 1.5 nmol/cm². This makes its possible to precisely determine Chla with a background of variable and high pigment concentration.