(407j) 3D Xylem Networks in Grapevine: Visualization and Numerical Analysis

Xylem vessels are the primary structures responsible for transporting water and nutrients from the roots to the leaves and fruit in a plant. The numerous xylem micro-conduits (diameter of order 100µm) in a plant form an interconnected network, allowing the plant to create a continuous water column at negative pressure driven solely by the surface tension in the leaves. Recent improvements in the tomography resolution have made it possible for the first time to visualize a three dimensional xylem network. We will present images of the xylem network for Vitis vinifera and the results of flow simulations that analyze the effects of network structure on the mechanism of water transport.

Due to the extreme negative pressures (sometimes exceeding -20 atm) in parts of the xylem network, individual tubes or larger parts of the xylem network often develop gas bubbles (embolisms) in solution, compromising the effectiveness of the transport pathway and rendering parts of the network unusable. A possible mechanism for bubble formation and the spread of vapor from embolized vessels to water-filled vessels will be presented. At a larger scale, a numerical analysis examining the effects of the removal of portions of the network will show that the xylem network structure is a compromise between 1) the efficiency of water transport and 2) safety against embolisms, pathogens, and structural damage.