Detection of water content in tomato stems by electrical impedance spectroscopy: Preliminary study

Abstract

Tomatoes lack drought-resistant genes, rendering seedlings susceptible to slow growth and death during drought stress. To gauge the water deficit in tomato plants, the electrical impedance spectra of tomato seedlings were measured at distinct water content levels (pristine, 92%, 91%, 90%, and 89%). These measurements tracked changes in water state, microstructure, and shear stress during water loss. The results revealed that impedance values and the real and imaginary parts decreased with increasing frequency, displaying a negative correlation with water content. Notably, the absolute mid-frequency slope (F2) exhibited an R2 of 0.9996, serving as an effective variable to characterize water content changes in tomato seedlings. Drought-induced alterations in stem cells shifted the seedling's equivalent circuit from the improved Hayden model to two parallel constant phase element (CPE) models. Concurrently, as water was lost, the proportion of free water diminished while water-binding capacity increased. This shift was accompanied by the wilting of cells, which reduced tissue rigidity, weakened ion conductivity, and altered the ratio of free water to bound water from 36.22 to 5.43. The pot experiment revealed that the F2 could be utilized to monitor the situation of short and sharp water shortages; however, additional research is required to explore its potential for long-term water monitoring. These findings establish a solid theoretical basis for monitoring water content in tomato plants in field settings.