Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada, T6G 2H1.
Plant Cell Environ. 2010 Mar;33(3):382-93. doi: 10.1111/j.1365-3040.2009.02088.x. Epub 2009 Nov 24.
The purpose of this study was to determine how shading affects the hydraulic and wood-anatomical characteristics of four boreal conifers (Pinus banksiana, Pinus contorta, Picea glauca and Picea mariana) that differ in shade tolerance. Plants were grown in an open field and under a deciduous-dominated overstory for 6 years. Sapwood- and leaf-area specific conductivity, vulnerability curves, and anatomical measurements (light and scanning electron microscopy) were made on leading shoots from six to nine trees of each treatment combination. There was no difference in sapwood-area specific conductivity between open-grown and understory conifers, although two of four species had larger tracheid diameters in the open. Shaded conifers appeared to compensate for small diameter tracheids by changes in pit membrane structure. Scanning electron microscopy revealed that understory conifers had thinner margo strands, greater maximum pore size in the margo, and more torus extensions. All of these trends may contribute to inadequate sealing of the torus. This is supported by the fact that all species showed increased vulnerability to cavitation when grown in the understory. Although evaporative demand in an understory environment is low, a rapid change into fully exposed conditions could be detrimental for shaded conifers.
本研究旨在确定遮荫如何影响耐荫性不同的四种北方针叶树（Pinus banksiana、Pinus contorta、Picea glauca 和 Picea mariana）的水力和木材解剖学特性。这些植物在开阔地和落叶主导的林冠下生长了 6 年。对来自每个处理组合的六到九棵树的领导枝条进行了木质部和叶片面积比导率、脆弱性曲线和解剖学测量（光镜和扫描电镜）。虽然四个物种中有两个在开阔地的导管直径较大，但在开阔地和林冠下生长的针叶树之间木质部面积比导率没有差异。遮荫的针叶树似乎通过改变纹孔膜结构来补偿小直径的导管。扫描电镜显示，林冠下的针叶树有更薄的边缘链、更大的边缘最大孔径和更多的环纹延伸。所有这些趋势都可能导致环纹密封不足。当所有物种在林冠下生长时，对空化的脆弱性增加，这证实了这一点。尽管林冠下的蒸散需求较低，但迅速转变为完全暴露的条件可能对遮荫的针叶树不利。
