Effects of freeze-thaw injury on parameters of distributed electrical circuits of stems and needles of Scots pine seedlings at different stages of acclimation

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Abstract
Frost hardening and frost injury of both the stems and needles of Scots pine (Pinus sylvestris L.) seedlings were studied by electrical impedance analysis. This impedance analysis was based on equivalent circuits with distributed circuit elements (DCE). A double-DCE model for stems and two single-DCE models for needles provided excellent fit to the experimental impedance data. However, the single-DCE model for needles which takes into account the asymmetry of the impedance arc proved more appropriate than the symmetric model. Several parameters changed in proportion to frost injury. In stems, extracellular resistance and one relaxation time decreased with increasing damage, whereas intracellular resistance remained relatively unchanged. In needles, the overall pattern for extracellular resistance and relaxation time was similar to that in the stem. Intracellular resistance remained approximately constant in the case of the symmetric DCE model. During frost hardening, both extracellular and intracellular resistance increased in stems. In needles, extracellular resistance increased but relaxation time decreased with hardening. The skewness of the impedance spectra in the Cole-Cole plot for needles increased with hardening. The coefficient for distribution of the relaxation time(s) did not change in either stems or needles with frost hardening but some changes were found with frost damage.

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