Christensen-Dalsgaard Karen K, Ennos Anthony R, Fournier Meriem
The University of Manchester, Faculty of Life Sciences, Jackson's Mill, Manchester M60 1QD, UK.
J Exp Bot. 2007;58(15-16):4095-105. doi: 10.1093/jxb/erm268. Epub 2007 Nov 26.
Roots have been described as having larger vessels and so greater hydraulic efficiency than the stem. Differences in the strength and stiffness of the tissue within the root system itself are thought to be an adaptation to the loading conditions experienced by the roots and to be related to differences in density. It is not known how potential mechanical adaptations may affect the hydraulic properties of the roots. The change in strength, stiffness, conductivity, density, sapwood area, and second moment of area distally along the lateral roots of two tropical tree species in which the strain is known to decrease rapidly was studied and the values were compared with those of the trunk. It was found that as the strain fell distally along the roots, so did the strength and stiffness of the tissue, whereas the conductivity increased exponentially. These changes appeared to be related to differences in density. In contrast to the distal-most roots, the tissue of the proximal roots had a lower conductivity and higher strength than that of the trunk. This suggests that mechanical requirements on the structure rather than the water potential gradient from roots to branches are responsible for the general pattern that roots have larger vessels than the stem. In spite of their increased transectional area, the buttressed proximal roots were subjected to higher levels of stress and had a lower total conductivity than the rest of the root system.
根部被描述为具有比茎更大的导管，因此具有更高的水力效率。根系自身组织的强度和刚度差异被认为是对根部所经历的负载条件的一种适应，并且与密度差异有关。目前尚不清楚潜在的机械适应性如何影响根部的水力特性。研究了两种已知应变会迅速降低的热带树种侧根沿远侧方向的强度、刚度、传导率、密度、边材面积和截面惯性矩的变化，并将这些值与树干的值进行了比较。结果发现，随着应变沿根部向远侧降低，组织的强度和刚度也随之降低，而传导率呈指数增加。这些变化似乎与密度差异有关。与最远端的根相比，近端根的组织传导率较低，强度高于树干。这表明，对结构的机械要求而非从根到枝的水势梯度，是导致根部导管比茎更大这一普遍模式的原因。尽管支撑近端根的横截面积有所增加，但它们承受的应力水平更高，总传导率低于根系的其他部分。
