Endogenous Circadian Rhythms in Plant Bioelectric Signals: Cross-Station Replication and Visitor-Driven Suppression in a Public Exhibition

We report a cross-station replication of endogenous circadian rhythms in plant bioelectric voltage, recorded continuously for 42 days at three independent sensor stations within a public science exhibition (Phänomena, Dietikon, Switzerland; March–April 2026). Three primrose (Primula vulgaris) stations were equipped with custom Biolingo bioelectric sensors (ESP32 + AD8232) and recorded autonomously through approximately 21,000 visitor interactions. We extracted DC-invariant spectral features from 5–10 second volt-age windows (n = 78,431 quality-filtered files) and fitted two-stage cosinor models with bootstrap 95% confidence intervals. All three stations show a robust 24-hour rhythm in the 1–5 Hz band power (bp1–5), with peak-to-trough amplitudes between 0.35× and 1.19× of mesor (R²med 0.72–0.87). Acrophase varies across stations from 05:00 to 11:00 local time. Critically, the rhythm survives an overnight-only restriction (18:00–09:00, no visitors) at all three stations, ruling out visitor presence as the rhythm driver. The most visi-tor-intensive station (faces of museum visitors triggering an emotion-recognition instal-lation) additionally shows a sharp daytime amplitude collapse coincident with exhibition opening at 09:00, consistent with the cardiovascular-mechanosensory coupling demon-strated in a companion study [20]. We argue that bp1–5—the spectral band most directly related to plant action-potential activity—carries an endogenous circadian signal in Primula vulgaris, and that this signal is modulated by sustained nearby human cardio-vascular activity in a manner consistent with frequency-selective mechanosensory transduction. From a biomimetic perspective, this demonstrates that the plant’s evolved bioelectric sensing apparatus can be leveraged as a live ambient biosensor for nearby human activity, complementing the more common biomimetic approach of replicating plant sensing in synthetic devices.