Electrical bioimpedance spectroscopy as a tool for non-destructive monitoring nitrogen supply in two lettuce genotypes

Accurate monitoring of nutrient supply is crucial for effective plant nutrition management. This study introduces a bioimpedance spectroscopy (BIS) approach to evaluate how lettuce genotypes respond to nitrogen (N) supply, illuminating the link between BIS and N metabolism. The research consisted of two parts: a preliminary experiment focusing on extracellular fluid resistance, followed by a second experiment involving five different N treatments applied to two lettuce genotypes. BIS spectra were recorded from 1 Hz to 100 kHz, with a total of 224 measurements. Plant physiological analyses assessed total and extracellular fluid nitrate (NO₃⁻) concentrations, pigment concentration, total N content, and cell membrane stability index. In the preliminary experiment, a significant negative correlation was observed between extracellular fluid NO₃⁻ concentration and extracellular fluid resistance (r = – 0.67). Furthermore, the frequency range around 63 Hz (R² = 0.97) appeared most sensitive to NO₃⁻ dynamics in the ‘Kobak’ lettuce genotype. In the two lettuce genotypes exposed to the five different N treatments, extracellular fluid resistance negatively correlated with total N and NO₃⁻ content (r = – 0.76 and – 0.73), while vacuole fluid resistance showed a moderate correlation (r = – 0.51). Cell membrane capacitance was also significantly correlated with membrane stability index (r = 0.68), indicating that low-N conditions reduce membrane charge storage. However, these correlations appeared highly genotype dependent. Heatmap-based hierarchical clustering of Z-score standardized BIS parameters further confirmed these genotype-specific patterns. Collectively, these findings suggest that BIS captures key aspects of N uptake and storage, particularly in the extracellular fluid compartment. Overall, BIS offers a robust, non-destructive method for monitoring N status and may enhance precision in nutrient management for lettuce and other crops, although the genotype-specific differences must be carefully considered.