Theoretical-empirical prediction model of ice content in wood based on electrical impedance characteristics

Trees that are exposed to subzero temperatures in winter are susceptible to freeze damage, which adversely affects tree physiological activities and wood end-use. Freezing stress threatens the survival of trees by inducing the accumulation of ice bodies within wood tissues. However, accurately assessing ice content in wood tissues remains a challenge. This study aimed to develop a theoretical-empirical prediction model of frozen water content (FWC) to evaluate the quantity of ice forming in wood tissues. Differential scanning calorimetry was employed to examine the changes in FWC of pine (Pinus koraiensis Siebold & Zucc.) and poplar (Populus simonii Carr.) wood tissues under a series of subzero temperature points at two cooling rates. The corresponding responses of specific extracellular resistance(r_e) and intracellular resistance(r_i) were obtained by electrical impedance spectroscopy. Experimental study showed that FWC increased as temperature decreased, with a notable transition around − 40 °C. The corresponding r_e initially increased and then decreased, peaking at − 40 °C. The change trend of r_i was consistent, but reached its peak value at − 30 °C. In the temperature ranges of 0 to − 30 °C and below − 40 °C, the specific theoretical linear models between FWC and r_i, and the logistic model of FWC at a semi-lethal temperature zone of − 30 °C to − 40 °C were respectively established for both wood species. The theoretically predicted values fitted well with experimental values, with the prediction error below 5%, verifying the validity of the theoretical model. This study provides new insights for exploring the freezing behaviors of water in wood and for assessing the mechanisms of winter damage to trees by nondestructive approaches.