Jagels Richard, Visscher George E, Lucas John, Goodell Barry
Department of Forest Ecosystem Science, University of Maine, Orono, ME 04469, USA.
Ann Bot. 2003 Jul;92(1):79-88. doi: 10.1093/aob/mcg117. Epub 2003 May 21.
The xylem of Metasequoia glyptostroboides Hu et Cheng is characterized by very low density (average specific gravity = 0.27) and tracheids with relatively large dimensions (length and diameter). The microfibril angle in the S2 layer of tracheid walls is large, even in outer rings, suggesting a cambial response to compressive rather than tensile stresses. In some cases, this compressive stress is converted to irreversible strain (plastic deformation), as evidenced by cell wall corrugations. The heartwood is moderately decay resistant, helping to prevent Brazier buckling. These xylem properties are referenced to the measured bending properties of modulus of rupture and modulus of elasticity, and compared with other low-to-moderate density conifers. The design strategy for Metasequoia is to produce a mechanically weak but hydraulically efficient xylem that permits rapid height growth and crown development to capture and dominate a wet site environment. The adaptability of these features to a high-latitude Eocene palaeoenvironment is discussed.
水杉（Metasequoia glyptostroboides Hu et Cheng）的木质部具有密度极低（平均比重 = 0.27）以及管胞尺寸相对较大（长度和直径）的特点。即使在外部年轮中，管胞壁S2层的微纤丝角也很大，这表明形成层对压缩应力而非拉伸应力作出了响应。在某些情况下，这种压缩应力会转化为不可逆应变（塑性变形），细胞壁起皱即为证明。心材具有一定的抗腐性，有助于防止巴西利尔屈曲。这些木质部特性与测得的抗弯强度模量和弹性模量相关，并与其他低密度至中密度针叶树进行了比较。水杉的设计策略是产生一种机械强度较弱但水力效率较高的木质部，以实现快速的高度生长和树冠发育，从而占据并主导潮湿的立地环境。本文讨论了这些特征对始新世高纬度古环境的适应性。
