Mechanical properties affecting the within-tree variation of microfibril angle

茎内幼龄材的微纤丝角(MFA)较大，不同树种和同一树种内的无性系差异较大。这表明MFA是遗传成分，但也受到树木生长变化因素的影响，如树木的力学性质。以具有不同MFA的日本柳杉无性系和MFA较小的云杉为材料，研究了树体结构，包括根系结构，并比较了在重力状态下形成的树干和树枝以及在非重力状态下形成的根材的木材性质。不同的无性系或树种具有不同的MFA和茎中的强度特性，其根系也不同。杉木幼龄无性系间的MFA差异在茎木材中较大，而在根材中较小，说明杉木幼林的MFA变异较大的是地上部分。根材偏心，不形成压缩材，其生长应力分布围绕中心不对称。

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.