When leaves flutter in the breeze, the frequency of their vibrations may indicate whether the plant is dehydrated. This finding could lead to new ways of monitoring farm crops and help us understand how rainwater reaches the forest floor.
Think of a leaf as a ruler held by one end while the other end is flicked, says at Cornell University in New York. A stiffer ruler will vibrate at a higher frequency than one that is more flexible.
Previous studies have found that the frequency of fluttering leaves goes down as they dry out. “That is intuitive because as it loses internal water pressure, the leaf will be more flexible,” says Jung.
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But some researchers have reported the opposite. Jung’s research, which was presented at a conference of the American Physical Society in November, explains the inconsistency.
After four days in which Jung didn’t water his soy plants, 60 per cent of their leaves curled up and became stiffer. The cells in the curling leaves were packed more densely, making water transport harder, which caused the edges to dry out faster than the centre. The frequency of vibrations in these leaves doubled.
The other 40 per cent of the leaves went slack; in these leaves, the vibration frequency decreased by 30 per cent. Jung thinks the leaves that curl up are the younger ones, though he hasn’t proved this yet.
The study is exciting because it helps to understand how rainwater enters an ecosystem, says , who studies leaf biomechanics at the University of Colorado in Colorado Springs. “During a common rainfall event, an average of 15 to 20 per cent of rainfall is intercepted by plants. The degree to which leaves vibrate because of raindrop impact or wind during rainfall events can influence the amount of water intercepted by the canopy,” he says. “It is extremely interesting that the leaf water status may influence rainfall interception totals.”
By analysing footage of crop fields and measuring the frequency of leaf vibrations, Jung hopes that software will be able to reveal whether the plants are experiencing water stress and give irrigation advice to farmers.
