Do leaves make waves? Detecting vibrations from rapid movements in the sensitive plant, Mimosa pudica

There is great current interest in the field of plant acoustics, including the potential for plants to both perceive and produce acoustic cues. Many plants emit high-frequency clicks under water stress or injury, and the growing root tips of corn seedlings produce audio-frequency clicks. We investigated the possibility that rapid plant movements produce acoustic cues in the form of plant-borne vibration, focusing on the leaf-folding movements of the sensitive plant, Mimosa pudica. We induced leaf-folding while recording vibrations from the leaf base using a laser vibrometer. Having recorded characteristic and relatively high-amplitude vibrations, we then assessed the source of the vibrations: the physiologic motor that drives movement, or the contact between moving parts of the leaf. Vibrations were produced when folding pinnules contacted neighboring pinnules and the rachis of the stem. The frequency range and amplitude of the vibrations are comparable to other vibrational cues that both plants and insects perceive and respond to. In nature, leaf folding is induced by contact with potential herbivores. Potential receivers of leaf-folding vibrations include the attacking herbivore, for which the leaf movement and vibration may constitute a multimodal startle display; nearby predatory insects, for which the vibration provides a cue of prey location; and leaves on the same or neighboring plants.