INFLUENCE OF DIFFERENT ELECTRODES AND TISSUES ON THE IMPEDANCE SPECTRA OF SCOTS PINE SHOOTS

Impedance spectra (20 Hz-1 MHz) of shoots of Scots pine (Pinus sylvestris L.) were measured using a circuit analyzer. Two types of electrodes were used: (1) polarizable silver needle electrodes, and (2) an electrolyte cell with reversible Ag/AgCl electrodes. The electrode impedance of the silver needle electrodes was high, especially at low frequencies, and was most prominent in impedance measurements of wood (xylem and pith). The impedance spectra of shoots changed over time with the growth stage of trees in the spring. In the case of quiescent trees, the impedance spectra of the shoot, bark (phloem and cortex), and wood differed from each other. All spectra were characterized by a strongly depressed center(s), which suggests a distribution of relaxation time(s).