## 2 Impedance Spectroscopy
### Scopes of Application
#### 2.1.2 Is Applied in Forest and Agriculture Management  
Structural changes observed in plants or animal tissue reflect the organisms' physiological state. In the case of plants, there are already strong indications that their impedance evaluation over a range of frequencies allows for the ascertainment of diverse physiological characteristics. For instance, phospholipid bilayers (phospholipids are a class of lipids that contain a hydrophilic head and a hydrophobic tail) are critical components of plants' cell membranes; lipid bilayers act as barriers to the passage of molecules and ions into and out of the cell and are revealed when an electrical field is applied to the plants. Consequently, changes in plant physiology are reflected in the different polarization processes taking place; their evaluation by Impedance Spectroscopy is typically carried out on the leaves, fruits, stems, or roots [52]. It is essential to analyze plants' roots to understand their interactions with soil and/or climate. For instance, optimal water and fertilizer usage may be established through the characterization of plant root systems, which provide conditions to maximize crop production and respective quality. For example, [PERSON] et al. [53] identified essential connections between the root tissue's capacitance and the roots' weight under dry and wet conditions through EleIS (experiments were carried out using a four-electrode configuration for frequencies varying between 10 Hz and 1 MHz). EleIS has also been used in plant roots to evaluate morphological indices [54] (experiments were performed using a four-electrode configuration for frequencies varying between 60 Hz and 60 kHz, inserting one electrode in the middle position of the stem while the other one was positioned on the bottom of the container filled with the nutrient solution where the root of the stem was placed), to assess cadmium pollution and freeze-thaw damage [55] (for the characterization, the authors used frequency sweeps in the 5-100 kHz interval, with an AC voltage difference of 10 mV, using a four-electrode configuration approach), to measure cold acclimation and root hypoxia [56] (the magnitude and phase angle of the electrical impedance were determined experimentally using a four-points acquisition configuration in the frequency range from 30 Hz up to 1 MHz, using an AC voltage level of 1 V), and to characterize mycorrhizal colonization [57] (the frequencies used for the characterization varied between 5 Hz and 100 kHz, for an AC voltage difference with an amplitude of 10 mV, utilizing a four-points measuring setup). Regarding the stem of the plants, EleIS measurements were used for in vivo, in situ, and non-destructive monitoring of the plant's physiology [58] (for the measurements, an AC voltage possessing an RMS amplitude of 500 mV was adjusted, while frequencies were swept logarithmically across the 50 Hz-4 MHz interval). The attached setup to the stem of the Nicotiana tabacum plant (used as a dicot plant model) was composed of a four-electrodes measuring points system and allowed for the successful linking of their living electrical characteristics to the stem's internal structure. [PERSON] et al. [59] introduced a nutritional index calculated using the impedance modulus values measured at the stem of tomato plants, using EleIS results (the data sweeps were obtained for frequencies starting at 100 Hz through 50 kHz, for a peak-to-peak value of the sinusoidal signal voltage of 0.4 V, using a four-points measuring configuration). [PERSON] and colleagues [60] gathered evidence of EleIS potential for earlier detection of plant diseases (they used in their study a four-points measuring setup and a range of frequencies starting at 1 kHz and extending up to 1 MHz). They observed differences in impedance spectra measured at the stem of young pine plants infected with the nematode _Bursaphelenchus xylophilus_.