Spectral properties of light conducted in stems of woody plants show marked seasonal differences suggesting a close relationship with photomorphogenesis

Optical properties of stems in woody plants were investigated in the winter-spring period, and compared with those in the summer-autumn period. In both periods light could enter the interior of the stems and was conducted efficiently along the axial direction. Vessels, fibers and tracheids were all involved in this axial light conduction. However, spectral properties of the light conducted by stems, differed in different periods. The light conducted in stems of the winter-spring period showed higher relative intensity ratios at wavelengths around 825 nm and 920 nm than that in stems of the summer-autumn period. Furthermore, in the winterspring period, stems of deciduous species conducted light at a wavelength around 825 nm at a higher relative intensity ratio than those of evergreen species. These seasonal variations and inter-specific differences in spectral properties of woody stems suggest a close relationship with rhythms of growth, substance metabolism and photomorphogenesis in plants.