The idea that plants emit and perceive sounds is among the most provocative claims in plant neurobiology. For decades it was relegated to pseudoscience (Luther Burbank's theory of plants responding to music and its New Age versions). But in recent years, rigorous research has produced concrete evidence that plants emit acoustic vibrations with biological significance and that some respond to specific frequencies. The field is young, methodologies are still developing, and the distinction between solid findings and exaggerated claims remains delicate.

Plant Acoustic Emissions: The Solid Evidence

Cavitation and ultrasonic clicks: the most solidly documented phenomenon. When a plant suffers water stress (drought), water columns in the xylem (the vascular tissue for water) break through cavitation (formation and collapse of vapor bubbles). Each cavitation event produces an ultrasonic click (frequencies of 20-300 kHz) that propagates through plant tissue and, as the study by Lacointe et al. (Science, 2023) demonstrated, also through the surrounding air. The intensity and frequency of ultrasonic clicks is proportional to the plant's water stress: a potential tool for non-invasive diagnosis of water stress in crops. The study by Khait et al. (Cell, 2023): researchers from Tel Aviv University recorded sounds emitted by tobacco and tomato plants both intact and under water stress or after mechanical cutting, using acoustic microphones placed 10 cm from the plant (in the air, without contact). The results: stressed plants emitted sounds at 20-100 kHz (ultrasounds, inaudible to humans) with a frequency of 30-50 clicks/hour. Non-stressed plants emitted approximately 1 click/hour. A machine learning algorithm could distinguish with 70% accuracy the type of stress (water vs. mechanical) from the shape of the clicks. Plants "scream" when they suffer: a provocative conclusion (and headline in many newspapers) that the researchers themselves later downplayed: there is no proof that the clicks are produced intentionally as communication, nor that other organisms receive and interpret them in the open field.

Plants Respond to Sound: The Evidence

The most controversial part of plant bioacoustics is plants' response to sounds. Response to mechanical vibration: research by Appel and Cocroft (2014, Oecologia) showed that Arabidopsis plants exposed to vibrations produced by feeding caterpillars (recorded and reproduced as mechanical vibrations through the stem) produced more glucosinolates (chemical defenses against caterpillars) compared to plants not exposed to vibrations. Plants distinguished vibrations from feeding caterpillars from those of wind or other insects. A highly cited result but difficult to replicate with identical methodologies. Response to specific frequencies: Monica Gagliano (2017, Oecologia) reported that corn root tips grow in the direction of a water source even when water flows through a closed tube (without vapor or VOC release), hypothesizing that roots "hear" the sound of flowing water. The proposed mechanism: root cells have structures sensitive to mechanical vibrations. Result contested and not replicated by other groups. The response of bees to flower frequencies: a more solid result than that on roots. Lavender exposed to vibrations at 200-400 Hz (in the frequency range of bee wings) produced more nectar. Bees visited flowers that vibrated more, preferring this nectar source. A plant-bee communication system through mechanical vibrations of petals? The mechanism remains to be clarified.

"Music" and Plants: Separating Science from Pseudoscience

The question "does music help plants grow better?" is one of the most searched on the Internet and is surrounded by much pseudoscience. What the research says: some studies show that exposure to specific sound frequencies (typically 100-2000 Hz, both classical music and pure sounds) can influence plant growth under controlled laboratory conditions. But results are highly variable between different studies and difficult to replicate. Low frequencies (50-200 Hz) can activate mechanosensitive ion channels on cell membranes, inducing responses similar to wind or thigmotropism. High frequencies (>5000 Hz) can interfere with photosynthesis through thermal effects on thylakoid membranes of the chloroplast. Classical music vs. heavy metal: no methodologically rigorous study has demonstrated a difference between music types. The meta-analysis by Creath and Schwartz (2004) on plant bioacoustics studies found inconsistent effects dependent on methodology. The current scientific verdict: some specific sounds at specific frequencies and intensities can influence some physiological responses of some plants under controlled conditions. The broader claim that "classical music helps plants grow better" is not supported by robust evidence. The "sound of water" and roots: some companies sell devices that emit sounds in the frequency range of water to increase root growth. There is no robust scientific evidence for these effects under real cultivation conditions.

Plant Bioacoustics in Agriculture: Potential Applications

If plants emit significant sounds in response to stress, plant bioacoustics could become an agricultural monitoring tool. Applications in development: diagnosis of water stress with ultrasonic microphones: arrays of microphones that detect xylem cavitation clicks in crops, allowing identification of field areas with water stress before visual symptoms appear. Potential advantage over precision irrigation: it intervenes before damage, not after. Early disease diagnosis: some fungal infections alter vascular tissue structure producing characteristic cavitation patterns. Preliminary studies show that xylem sound changes in infected plants before visual symptoms. Not yet in commercial application. Ultrasonic stimulation for germination: some research (mainly from China, India) shows that exposure to ultrasounds (20-100 kHz) during germination accelerates germination and initial growth in some crops. Hypothesized mechanism: ultrasounds increase cell membrane permeability, facilitating seed imbibition. Promising results but with high variability between species and conditions. Acoustic deterrence of herbivores: some frequencies in the 50-200 Hz range appear to deter some herbivorous insects. Studies on aphids and mites show population displacement from plants exposed to specific frequencies. Not yet in commercial application.

How to Study Plant Sounds: The Techniques

Plant bioacoustics requires specialized equipment and rigorous methodologies to distinguish biologically relevant sounds from background noise. Ultrasonic microphones (ultrasonic microphones): piezoelectric or condenser sensors in direct contact with the stem or leaves (solid conduction) or positioned in the air near the plant. Microphones must have a flat response up to 300-500 kHz to capture cavitation clicks. Anechoic chambers: rooms with walls of sound-absorbing material that eliminate reflections and ambient background noise. Indispensable for precise experiments. Background noise (ventilation, traffic, equipment) can mask biological signals. Frequency analysis (FFT: Fast Fourier Transform): algorithms that decompose the recorded acoustic signal into its frequency components, allowing identification of characteristic patterns of cavitation clicks or other biological signals. Machine learning for classification: machine learning algorithms trained to recognize the type of stress (water, mechanical, pathogenic) from the shape of ultrasonic clicks. Used in the Khait et al. (2023) study. Laser interferometry for leaf vibrations: lasers that measure micro-vibrations of the leaf surface (similar to a Doppler laser velocimeter) without physical contact. Allows measurement of vibrations produced by insects walking on leaves and the leaf's response to external vibrations. Plant bioacoustics is still in its infancy as a discipline: standardized protocols are lacking and methodologies vary enormously between laboratories, making result replication difficult.