TREES MAKE SOUNDS DURING DROUGHT CONDITIONS
Under drought-like conditions, bubbles formed inside the vascular tissues of trees emit sounds. According to researchers at Grenoble University in France who presented this research at last month’s American Physical Society meeting in Baltimore, Maryland, these sounds can alert us to trees in desperate need of water during droughts.
Within trees, there are two types of vascular tissues: xylem and phloem. Phloem transports sugars and proteins used for energy from photosynthetic sources (i.e. leaves) to the parts of the plant that do not produce energy (i.e. roots). Xylem is responsible for lifting water and nutrients from the roots to the leaves and other structural parts of the plant. These tubes make use of the attractive forces present between water molecules and the cells of the plant to lift water against the force of gravity to these upper areas.
Under conditions when adequate water is available, the water in the xylem is highly pressurized due to the small circumference of the tubes and the height of the trees. However, during drought conditions, pressure on the water in the xylem increases in the tree’s attempt to extract more water from the ground. As a result, air bubbles can become trapped in the xylem tubes, which block the water from moving freely through the xylem. The blockages of water movement are called cavitations, and can kill trees.
The researchers wanted to detect when cavitations occur inside the xylem, so they mimicked the body of a tree by slicing a thin section of pine and placing it into a liquid-filled gel capsule. By evaporating the water from the capsule, the scientists created drought-like conditions. Cavitations were recorded on film and with a microphone. A range of sounds was recorded from the mock drought, but the cavitations made a specific sound pattern and were detected and differentiated. The sounds were matched with images of the xylem captured under light transmission microscopy to ensure that the sounds were produced from the cavitations. The tree samples in this study were tested under extreme conditions, however, so testing this on larger trees in real-world conditions may yield differing results.
This study could potentially lead to specially designed microphones that can be used on trees to detect whether they are in danger from succumbing to drought-related deaths. Potentially, this device could be linked to an emergency watering system that can be activated, if necessary. Drought-like conditions are a potential result of our changing climate, and this is one way to combat those effects to save plant life.
-Jeanne K.
Photo courtesy of Peter Firminger.
References: http://meetings.aps.org/Meeting/MAR13/Event/189852