Bending and Squeezing: Gradual Electric Potentials Encode Mechanical Stimuli in Poplar

Mechanical stimuli such as wind elicit rapid electrical signals in plants, yet the mechanisms underlying these responses remain poorly understood. Here, we investigated the electrophysiological responses of young poplar trees to controlled stem bending. We identified a gradual potential (GP), distinct from classical action potentials, whose attenuation and propagation distance depend strongly on stimulus speed and intensity. While the maximal GP amplitude recorded near the bending site remained stable across stimulation conditions, slower or gentler flexions resulted in faster spatial decay and shorter propagation distances. Similar GP responses were elicited by stem bending and by direct root pressurization, indicating a coupling between hydraulic perturbations and electrical signaling. Although GP propagation and attenuation are consistent with a diffusive pressure signal, key features-such as the invariance of peak amplitude at generation site and progressive waveform narrowing-cannot be explained by hydraulic diffusion alone and point to a nonlinear transduction process. Together, these results constrain the biophysical mechanisms underlying mechanically induced electrical signaling in trees and provide a framework for future studies addressing their physiological relevance.