Xylem Network Model

GIF of the new flowering plant xylem network model showing the process of cavitation. Black vertical lines are vessels and red horizontal lines are intervessel connections (IVCs). ΔP is the pressure difference between the water and the atmosphere. As the pressure difference increases, emboli propagate and embolize some vessels (cyan) while isolating others (magenta).

Without water plants can’t photosynthesize. Without photosynthesis plants can’t produce the sugar required to grow or produce the fruits and vegetables so many organisms depend on, including all of us. To become better informed on how plants will react to our ever-changing climate, investigating the fragility of plant water use and its adaptive capabilities is paramount.

Xylem, the water conductive tissues of plants, uses a delicate combination of physics, biology, and alleged chemistry to move water against gravity. Any attempt to directly observe xylem functioning in detail (such as cutting wood, inserting probes,…) almost always makes it obsolete due to how fragile the water transport mechanism is. Since humanity still heavily needs to understand this process for many reasons, we developed a computational program to mimic xylem function.

We used the object-oriented capabilities of Matlab, a powerful computational tool developed by MathWorks. As shown in the above GIF, water goes “up” from the roots to the leaves through ducts called vessels in flowering plants. However, no vessel spans the whole length of the plant so water has to flow horizontally from one vessel to the other through vessel contact walls. It may seem like a like not to use a single duct to transport all the water from the roots to the leaves until you realize what happens when a prolonged drought makes available water scarce.

When a drought persists and soil water decreases in quantity, the soil and the leaves of the plant start competing for the same water like in a tug of war: the leaves high up and the soil below the plant. The water inside the trunk of the tree, however, is not as strong as the rope you always use and can therefore break. When a water column breaks inside a vessel, an air bubble fills it up and inhibits further water movement (in cyan in the above GIF). This is why it is important that the plant depend on multiple vessels for water. If one vessel is filled with an air bubble, the plant can still depend on the other ones for water. It really is fascinating how, for hundreds of millions of years, plants have relied on such an apparently fragile mechanism.

The model simulates water flow, air bubble formation and its propagation. It elucidates how different anatomical characteristics of flowering plants affect the vulnerability of plants to water scarcity and ensuing bubble formation. We submitted a manuscript that is currently under review. The Matlab code used is online on Github and you can access the all important Readme file on this link.