No abstract

Bamboos are among the largest woody grasses and grow very rapidly. Although lignin is a crucial factor for the utilization of bamboo biomass, the lignification mechanism of bamboo shoots is poorly understood. We studied lignification in the bamboo Sinobambusa tootsik during culm development. Elongation growth began in May and ended in late-June, when the lignin content was approximately half that in mature culms. Thioacidolysis analysis indicated that p-hydroxyphenyl units in lignin formed even at late stages of lignification. The syringyl/ guaiacyl ratio varied during culm development. Various lignin precursors were detected in developing culms by liquid chromatography-mass spectrometry. The ferulic acid content decreased from May to June, indicating that ferulic acid was utilized in early stages of cell wall formation. Monolignol glucosides were detected at early stages of lignification, whereas the contents of monolignols, coniferaldehyde, sinapaldehyde, p-coumaric acid, and ferulic acid peaked at later stages of lignification. Therefore, lignin precursors may be supplied differentially during the lignification process. In August, the rate of lignification decreased, although the contents of various lignin precursors peaked, implying that the rate-limiting step in the cessation of lignification in bamboo is transport or polymerization of lignin precursors, rather than their biosynthesis.

To promote the use of sugi woods, the information on the variation of wood properties is very important. Obisugi is a major group of sugi cultivars planted in Southern Kyushu. However there is no information on the variation of wood properties with height position in the stems of Obi-sugi trees. We examined in detail the difference between the wood properties at 5 m above ground upper height position and those at 1.5 m above ground lower height position of Obi-sugi cultivars. Obtained results were as follows : Mechanical properties in both mature and juvenile wood at the upper height position were higher than those at the lower height position in most cultivars. Radial variations of mechanical properties at the upper height position were larger than those at the lower height position in most cultivars. Microfibril angle of latewood tracheids MFA in both mature and juvenile wood at the upper height position was smaller than those at the lower height position in most cultivars. On the other hand, basic density and latewood tracheid length in both mature and juvenile wood at the upper height position did not differ from those at the lower height position in many cultivars. Higher mechanical properties at the upper height position were mainly the result of the decrease of MFA with height position. In addition, to examine the whole tree variation from top to bottom, we investigated the variation of wood properties of Obi-sugi trees at different height increments. The results suggested that longitudinal variations of mechanical properties were well explained by variations of MFA and basic density, and that height increment affected the mechanical properties and the longitudinal variation pattern of wood properties. Keywords :Obi-sugi cultivars, wood property variation, microfibril angle, basic density, height increment.

It was previously believed in Japan that the wood qualities of hinoki (Chamaecyparis obtusa) were superior to sugi (Cryptomeria japonica). However, few studies of wood properties such as MFA (microfibril angle of S 2 layer in secondary wall of tracheid) have been completed for hinoki. Some reports have found that hinoki plus tree families have similar mechanical properties to sugi. Here we report the characteristics of MFA and density of hinoki half-sib families in a progeny test stand. There were significant differences in MFA and density between families. The wood properties of two families, Nakatsu 3 and Kanzaki 5, are stable in radial pattern and suitable for structural use. Early selection of hinoki families by MFA and density may be difficult. Effects of MFA and density on E d (dynamic modulus of elasticity) of logs differed between families. The effects of growth rate on MFA and density differed between families and also between juvenile and mature wood. The faster growth rate in Nakatsu 3 appeared to improve wood properties and increase E d of logs, although in many other families, faster growth rate had negative effects on desirable wood properties for structural use.

A modified confocal laser scanning microscopy (CLSM) system was developed not only to observe the microcracks on the surface of Cryptomeria japonica D. Don in situ at the cellular level but also to obtain information about the moisture content (MC) of the wood surface by measuring the change in its electrical resistivity. The sequential images and changes in the electrical resistivity of the wood surface indicated that microcracks formed between the tracheid and ray parenchyma in the latewood region at >1.0E + 07 Ω/sq (square). Microcracks formed when the MC of the wood surface was below the fiber saturation point determined through regression analysis of the surface electrical resistivity and MC. Most of the microcracks develop when the surface electrical resistivity ranged from 3.95E + 10 to 3.60E + 12 Ω/sq. When the surface MC was ∼2.5%, microcracks closed and the surface electrical resistivity was either ∼1.00E + 15 Ω/sq or outside the measurement range. The modified CLSM and the method to measure the MC of the wood surface can be used to acquire information about the surface MC in specific areas shown in CLSM images. The findings indicated that the MC of the surface of the wood plays an important role in suppressing the emergence of microcracks in drying wood. The modified CLSM system and the method of measuring the MC of the surface of wood can be used to efficiently evaluate methods of drying wood and the quality of dried wood.