Advancing nitrogen diagnostics in plants through bioimpedance spectroscopy: current evidence and future perspectives—a review

Nitrogen (N) is an essential macronutrient that plays a central role in photosynthesis, metabolism, and crop productivity. Accurate and non-destructive evaluation of plant N status is essential for improving N use efficiency and sustainable fertilization. Bioimpedance spectroscopy (BIS) has emerged as a promising tool for in vivo assessment of plant physiological state; however, its application to nutrient monitoring remains limited. Previous studies show that N deficiency significantly alters extracellular and intracellular fluid resistances and reduces cell membrane capacitance, reflecting impaired ion conductivity, loss of membrane integrity, and changes in vacuole storage. These alterations can be detected in vivo within specific frequency ranges and often correlate with leaf N content, but most studies considered only total N and did not account for inorganic nitrate (NO₃⁻) forms or water-related effects. Future research should combine BIS with direct apoplastic NO₃⁻ measurements and factorial N and water experiments to distinguish nutrient-specific responses from drought-induced changes. Applying advanced equivalent circuit models, such as the Double-Shell (DBS) model, could strengthen physiological interpretation and associate impedance parameters with cellular functions. Addressing these issues will enable BIS to become a reliable, non-destructive diagnostic method for N monitoring.