Abstract
Fluid flow between adjacent tracheids is realized through bordered pits in the xylem of conifers. The pit has an extremely small size and a highly complex structure. This paper presents a mesoscopic analytical method for the relationship between the pit structure and its hydraulic characteristics through mathematical modeling using the lattice Boltzmann method (LBM) and curved boundary treatment. Mongolian Scots pine were selected as the research subject of this study, and the bordered pit structure parameters was collected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the original geometric features were maintained for direct modeling analysis. The model revealed the relationship between various components of the bordered pit and liquid flow velocity/resistance, indicating that margo is the main factor affecting flow resistance. Further anatomical investigation separately analyzed the influence of change in a single factor, including pit diameter, pit aperture diameter, pit depth, torus diameter, and margo thickness, on the overall flow and pressure drop to confirm the importance of various factors in this relationship. Additionally, the influence of pore size and pore location distribution in the margo on the flow rate and pressure drop was further analyzed quantitatively. The results showed that the flow rate through individual pores is the result of the combined effect of pore area and radial position of the pore in the margo. Our study promotes the research and application of the mesoscopic model LBM in simulating flow conditions in the complex flow field of pits, which realizes the numerical analysis of the flow field model based on individualized real bordered pits. In comparison with the classical macroscopic model, the accuracy and effectiveness of the proposed model are proved. This research can provide a promising method for analyzing the physiological and ecological functions of conifer and realizing the efficient utilization of wood resources.
Highlights
Bordered pits play an important role in conducting water through the xylem, and act as a bridge to transport water or nutrients between tracheids [1,2]
By modifying the curved boundary processing scheme, we proposed the use of lattice Boltzmann method (LBM)-C method to analyze the complex flow field inside the pit, and obtained the relationship of the bordered pit structure components with velocity, flow rate, pressure drop, and resistance
The results show that when the diameter of the pit increased, flow rate increased, whereas total pressure drop decreased
Summary
Bordered pits play an important role in conducting water through the xylem, and act as a bridge to transport water or nutrients between tracheids [1,2]. Bordered pits of Mongolian Scots pine, a coniferous tree species, were selected as the research subject of this study (Figure 1). A primary thickening, known as torus, is formed in the middle of the pit membrane on the axial tracheid wall (Figure 1c,f), which is generally considered to be non-water-conducting. The diameter of the torus is usually larger than that of the pit aperture, and it acts as a piston to regulate the intertrachedral fluid flow. The pit membrane contains a complex network composed of Forests 2021, 12, 526.
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