Bioimpedance spectroscopy highlights bioelectrical mechanisms of nitrogen and water interactions in cucumber leaves

Nitrogen (N) and water together significantly influence plant cell electrophysiology and stress responses, but monitoring these effects in soil-grown plants remains challenging. The aim of this study was to test whether bioimpedance spectroscopy (BIS) can detect changes in leaf electrical properties caused by different N supplies and water availability in soil-grown cucumber plants. We used BIS to measure leaf electrical properties in cucumber plants exposed to four N treatments: nitrate (NO 3 − ), mixed ammonium-nitrate (NH 4 NO 3 ), wool pellets containing NH 4 and organic N (WP), and no N (CTRL), across four phases: full nutrition, limited nutrition, drought stress, and rehydration. BIS spectra were interpreted within a Double-Shell model, in which the fitted parameters were treated as indirect electrical descriptors with compartment-level physiological relevance. BIS spectra were recorded from 1 Hz to 100 kHz. Under full and limited nutrition, NO 3 − and wool pellets treatment reduced extracellular fluid resistance and increased cell membrane capacitance compared to the control. The NH 4 NO 3 treatment maintained higher extracellular fluid resistance. Wool pellet treatment increased intracellular and vacuole fluid resistance, consistent with slow N release. Drought stress increased extracellular fluid resistance and lowered cell membrane capacitance; changes were smaller with NH 4 NO 3 . Vacuole fluid resistance increased in control and wool pellet treatment and remained lowest under NO 3 − . After rehydration, extracellular fluid resistance decreased in NO 3 − and wool pellet-treated plants; recovery was moderate in NH 4 NO 3 and weak in the control. In addition, strong associations were observed among N supply, leaf pigments, and vacuole fluid resistance. This study provides insight into the potential application of BIS for monitoring N and water interactions in plants, particularly under soil-grown conditions; however, the biological specificity of the fitted model parameters requires further validation.