Thirsty trees emit ultrasonic popping sounds when stressed by drought.

In 2023, researchers at Tel Aviv University led by Lilach Hadany published groundbreaking findings in the journal Cell, documenting tomato and tobacco plants emitting sounds during drought stress. These ultrasonic clicks occur between 20 and 100 kilohertz—well above the human hearing threshold of approximately 20 kilohertz. The sounds result from cavitation, a physical process where air bubbles form, expand, and collapse within the plant's xylem vessels.The xylem is the tissue network that transports water and minerals from roots to leaves. During water scarcity, tension within these tubes intensifies until the water column fractures, creating air pockets. Each bubble collapse generates a mechanical vibration that travels through plant tissue and can be detected by sensitive microphones from several meters away.Using machine learning to analyze recordings, the research team discovered they could identify different types of plant stress by their acoustic signatures. Drought-stressed plants, for instance, produced distinctly different sounds than mechanically damaged ones. This finding revealed that the plant kingdom generates far more acoustic activity than previously recognized.Although humans cannot perceive these sounds, scientists hypothesize that insects such as moths and small mammals like mice may detect them from up to 5 meters away. This capability could shape how these creatures interact with plants—influencing egg-laying site selection or feeding choices. This discovery opens new possibilities for farmers to monitor crop health through acoustic sensors, offering an alternative to traditional visual assessment methods.