Mechanical properties affecting the within-tree variation of microfibril angle

幼龄材茎内的微弯角较大，且不同树种和同一树种内的无性系间存在差异。这表明，MFA是遗传成分，但它也受到树木生长变化的因素，如树木的力学性质。以MFA不同的日本柳杉无性系和MFA小的云杉为材料，研究了包括根系在内的树木结构，并比较了重力作用下形成的干材和分支材与无重力作用下形成的根材的木材性质。不同无性系或种的根系具有不同的MFA和强度特性。不同无性系幼龄材间MFA的差异在茎材中较大，而在根材中较小，说明幼龄材MFA的差异仅表现在地上部。根材偏心，不形成压缩材，生长应力分布不对称。

Microfibri angle (MFA) is large in the juvenile wood within stem, and is different by species and clones within the same species. It suggests that MFA is genetic component, but also it is affected by a factor changing by tree growth such as tree mechanical properties. Tree structure including the root system was examined, and the wood properties were compared between the stem and branch wood formed under gravitation and the root wood formed under gravity-free state, using sugi (Cryptomeria japonica) clones having different MFA and spruce having small MFA. The root systems were different by clones or species having different MFA and strength properties in the stem. The MFA difference between young sugi clones were large in the stem wood, but small in the root wood, which suggested that the large MFA variation in the sugi juvenile wood is observed only above the ground. The root wood was eccentric, didn't form the compression wood and its growth stress distribution was not symmetric about the center.