School of Life Sciences, University of Nevada - Las Vegas, Las Vegas, NV 89154, USA.
New Phytol. 2012 Feb;193(3):721-729. doi: 10.1111/j.1469-8137.2011.03986.x. Epub 2011 Dec 5.
• The flow of xylem sap through conifer bordered pits, particularly through the pores in the pit membrane, is not well understood, but is critical for an understanding of water transport through trees. • Models solving the Navier-Stokes equation governing fluid flow were based on the geometry of bordered pits in black spruce (Picea mariana) and scanning electron microscopy images showing details of the pores in the margo of the pit membrane. • Solutions showed that the pit canals contributed a relatively small fraction of resistance to flow, whereas the torus and margo pores formed a large fraction, which depended on the structure of the individual pit. The flow through individual pores in the margo was strongly dependent on pore area, but also on the radial location of the pore with respect to the edge of the torus. • Model results suggest that only a few per cent of the pores in the margo account for nearly half of the flow and these pores tend to be located in the inner region of the margo where their contribution will be maximized. A high density of strands in outer portions of the margo (hence narrower pores) may be more significant for mechanical support of the torus.
• 针叶树边缘纹孔中木质部汁液的流动，特别是通过纹孔膜上的孔隙的流动，还没有被很好地理解，但对于理解树木中的水分运输至关重要。 • 基于黑云杉（Picea mariana）边缘纹孔的几何形状和显示纹孔膜边缘处孔隙细节的扫描电子显微镜图像，建立了用于解决控制流体流动的纳维斯托克斯方程的模型。 • 结果表明，纹孔腔对流动阻力的贡献相对较小，而环带和纹孔膜边缘孔隙的贡献较大，这取决于单个纹孔的结构。单个纹孔膜边缘孔隙的流动强烈依赖于孔隙面积，但也依赖于孔隙相对于环带边缘的径向位置。 • 模型结果表明，纹孔膜边缘的孔隙中只有百分之几的孔隙占近一半的流量，而且这些孔隙往往位于环带的内区，在那里它们的贡献将最大化。环带外区（因此孔隙较窄）的大量韧皮纤维可能对环带的机械支撑更为重要。
