Kiyotsugu Yoda, Mitsuo Suzuki and Hitoshi Suzuki

A new type of dendrometer, comprising two reflection type photointerruptors and flexible mirrors, was developed to record precisely the diameter changes of tree trunks, and the practicality of this device was examined. The maximum resolution of the detector was 600 nm, due to the quantization noise of A /D conversion. Measurement in the laboratory at a constant temperature demonstrated fluctuations in the output of only three bits of A /D conversion, corresponding to a change of c. 3.6 μm in diameter. There was no thermal drift of the device during measurements. Diameter changes of sapling stems and /or a tree trunk of Castanospermum australe (Leguminosae) and Zelkova serrata (Ulmaceae) were measured by this device. In addition to steadily thickening growth and diurnal diameter changes, all the plants showed spikelike diameter changes of the order of minutes, the discovery of which illustrates the superior performance of this new type of dendrometer.

Qiang Sun, Kiyotsugu Yoda and Hitoshi Suzuki

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 winter– spring 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.

Mitsuo Suzuki, Kiyotsugu Yoda and Hitoshi Suzuki

Initiation of vessel formation and vessel maturation indicated by secondary wall deposition have been compared in eleven deciduous broadleaved tree species. In ring-porous species the first vessel element formation in the current growth ring was initiated two to six weeks prior to the onset of leaf expansion, and secondary wall deposition on the vessel elements was completed from one week before to three weeks after leaf expansion. In diffuse-porous species, the first vessel element formation was initiated two to seven weeks after the onset of leaf expansion, and secondary wall deposition was completed four to nine weeks after leaf expansion. These results suggest that early maturation of the first vessel elements in the ring-porous species will serve for water conduction in early spring. On the contrary, the late maturation of the first vessel elements in the diffuse-porous species indicates that no new functional vessels exist at the time of the leaf expansion.