Kiyotsugu Yoda

Phenological Comparison of the Onset of Vessel Formation Between Ring-Porous and Diffuse-Porous Deciduous Trees in a Japanese Temperate Forest

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.

Remote sensing methods for the evaluation of the mesquite tree (Prosopis juliflora) environmental adaptation to semi-arid Africa

In this study a remote sensing approach for the mesquite tree (Prosopis juliflora) control is proposed. The mesquite tree is well known for its high adaptability to arid and semi-arid conditions and characterized by very high water use efficiency. Introduction of the mesquite has caused several environmental problems in Sudan. In this study, to monitor mesquite water use efficiency the concept of a Normalized Difference Infrared Index (NDII), which is defined as the ratio of actual to foliar water content, have been applied and compared with the ground measurements of stomatal conductance (mmol. m-2. s-1), field spectral, volumetric soil water content. As results, on the base of the PALSAR L-band microwave polarimetric backscatter coefficient, the soil moisture (in bare soil area) and surface roughness (in dense forest covered area) could be estimated with a good accuracy for bare-soil surfaces.

DEVELOPMENT AND EVALUATION OF A NEW TYPE OF OPTO-ELECTRONIC DENDROMETER

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.

Diurnal fluctuation of groundwater levels caused by the invasive alien mesquite plant.

Invasive alien plants such as mesquite (Prosopis juliflora) alter patterns of groundwater uptake. We measured the groundwater level beneath a mesquite stand in an arid area in Sudan. The changes in groundwater level closely followed plant water uptake. The groundwater level started to decline a few hours before sunrise, recovered around noon, and then continued to decline until a few hours after sunset, before recovering again during the night. Thus, groundwater level showed two peaks: just before sunrise and around midday. The midday recovery was due to the depression of photosynthesis by heat and light.

SPECTRAL PROPERTIES OF LIGHT CONDUCTED IN STEMS OF WOODY PLANTS SHOW MARKED SEASONAL DIFFERENCES SUGGESTING A CLOSE RELATIONSHIP WITH PHOTOMORPHOGENESIS

SUMMARY 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 spec tral properties of woody stems suggest a close relationship with rhythms of growth, substance metabolism and photomorphogenesis in plants.

Evaluation of the Effect of a Rain Pulse on the Initial Growth of Prosopis Seedlings

Prosopis juliflora is a useful “multi-purpose” tree, but it invades rapidly in arid and semi-arid environments, causing livelihood degradation of local communities. A rain pulse under drought conditions has been reported to be an important factor to promote plant invasion. The purpose of this research was to evaluate the effect of a rain pulse on the invading process of Prosopis juliflora and to propose a feasible plan to control the expansion of this species in Sudan. First, seed germination was examined under eight irrigation conditions, corresponding to 4–32 mm of rainfall. Most seeds imbibed in all the irrigation conditions, about half or more of the imbibed seeds germinated in 12 mm or more of irrigation. Twenty mm or more of irrigation induced seed emergence. Second, initial growth of germinated seeds was examined under ten irrigation conditions (1–32 mm rainfall) over 54 hours or 138 hours of cultivation. Radicle elongated most vigorously in 24 mm irrigation, and extended over 20 cm in length. Allocation to radicle was dominant, and its elongation was promoted in higher soil moisture condition. Based on these results, we propose that seedlings of P. juliflora should be eradicated within a few weeks after a single large rainfall, which might be convenient and effective to control additional expansion of this species in Sudan.