Measurement of Fluorescence spectra in Tree Leaves by Multi-wavelength Excitation

Abstract

In this study, we measured the fluorescence spectra in 30 species of tree leaves by excitation at multiple wavelengths from 300 nm to 440 nm each season. Variations of spectral transmittance in the upper epidermis were estimated based on the fluorescence spectra changes. In addition, chlorophyll contents (SPAD), anthocyanin contents (ACI), and photosynthetic activity (Fv/Fm) of the leaves were measured. The findings showed that there was a good correlation between chlorophyll fluorescence intensity ratio F740/F685 under excitation at 440 nm and SPAD in deciduous trees. In some tree species, F450 and F530 increased at specific excitation wavelengths. In all seasons, the relative spectral transmittance at a wavelength of 300 nm (RT300) was lower in evergreen trees than in deciduous trees. In evergreen trees, there was a good correlation between RT300 and F530 under excitation at 420 nm. In autumn deciduous trees, the larger RT300 was, the smaller Fv/Fm was. In evergreen trees, there was a correlation between the relative spectral transmittance at a wavelength of 360 nm (RT360) and F450 under excitation at 360 nm. These results suggest that seasonal variation of the fluorescence spectra and spectral transmittance in the upper epidermis of tree leaves are closely related to pigments and photosynthetic activity in the leaves. Therefore, measurement of fluorescence spectra in tree leaves by multi-wavelength excitation is useful for the characterization of tree leaves.