Aumann Craig A, Ford E David
Department of Biological Sciences, University of Alberta, Edmonton AB, T6G 2E9, Canada.
Tree Physiol. 2006 Mar;26(3):285-301. doi: 10.1093/treephys/26.3.285.
A tracheid-level model was used to quantify the effects of differences in wood microstructure between coastal and interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii and var. glauca) wood on larger scale properties like hydraulic conductivity. The model showed that tracheid length, the ease of flow through a bordered pit and effective tracheid diameter can all limit maximum hydraulic conductivity. Among the model parameters tested, increasing bordered pit conductivity and tracheid length resulted in the greatest increase in maximum conductivity in both the inland and coastal ecotypes. A sensitivity analysis of the uncertainty between parameters governing flow through the bordered pit and air-seeding potential showed that, although decreased pit flow resistance increased maximum hydraulic conductivity, increased cavitation led to lower conductivity over time. The benefits of increasing the number of bordered pits depended on the intensity of the meteorological driving function: in drier environmental conditions, wood with fewer pits was more conductive over time than wood with more pits. Switching the bordered pit characteristics between coastal and interior wood indicated that the conductivity time course of coastal and interior wood was primarily governed by differences in the number of bordered pits and not differences in tracheid dimensions. The rate at which tracheids refilled had little effect on the conductivity time course of either coastal or interior wood during the first two summers when the wood was highly saturated, but had a marked influence in subsequent years once the cavitation profile stabilized. Our work highlights the need for more empirical work on bordered pits to determine whether variation in their number and properties is related to changing environmental conditions. In addition, a detailed simulation model of a bordered pit is needed to understand how variation in pit properties affects the relationship between ease of flow through a bordered pit and its potential for facilitating air-seeding.
采用管胞水平模型来量化沿海和内陆花旗松（Pseudotsuga menziesii (Mirb.) Franco var. menziesii和var. glauca）木材微观结构差异对诸如水力传导率等较大尺度特性的影响。该模型表明，管胞长度、通过具缘纹孔的流动难易程度以及有效管胞直径均会限制最大水力传导率。在所测试的模型参数中，增加具缘纹孔传导率和管胞长度会使内陆和沿海生态型的最大传导率增幅最大。对控制通过具缘纹孔的流动和空穴播种潜力的参数间不确定性进行的敏感性分析表明，尽管纹孔流动阻力降低会增加最大水力传导率，但随着时间推移，空穴化增加会导致传导率降低。增加具缘纹孔数量的益处取决于气象驱动函数的强度：在更干燥的环境条件下，随着时间推移，具较少纹孔的木材比具较多纹孔的木材传导性更强。将沿海和内陆木材的具缘纹孔特征进行切换表明，沿海和内陆木材的传导率时间进程主要由具缘纹孔数量差异而非管胞尺寸差异所决定。在前两个夏季木材高度饱和时，管胞重新充水的速率对沿海或内陆木材的传导率时间进程影响很小，但在空穴化剖面稳定后的后续年份中影响显著。我们的工作凸显了对具缘纹孔开展更多实证研究的必要性，以确定其数量和特性的变化是否与不断变化的环境条件相关。此外，需要一个详细的具缘纹孔模拟模型来了解纹孔特性的变化如何影响通过具缘纹孔的流动难易程度与其促进空穴播种潜力之间的关系。
