Seasonal Dynamics of Electrical Impedance and Electrical Capacitance of the Pre-Cambial Complex of Tissues in the Trunks of Scots Pine Trees Growing in a Natural Forest Stand
Introduction. The radial growth of woody plants is directly related to the activity of the pre-cambial complex of tissues (PCT) of the trunk; the state of the tissues is studied by bio-impedance measurements. The analysis of information about the nature of electrical impedance (EI) of plant tissues shows that it depends on the tissue structure and physiological state. The use of EI measurements makes it possible to determine the values of intercellular and intracellular resistance, as well as membrane capacitance. The aim of the study was to investigate seasonal dynamics of EI characteristics of PCT of the trunks of Scots pines growing in natural forest stands and to establish the relationship between these parameters and the processes of tissue growth and differentiation. The object of the study was a natural stand of old-aged Scots pine trees (age class VII) located on the territory of the arboretum of the Botanical Garden of the Ural Branch of the Russian Academy of Sciences (Yekaterinburg). The measurements were carried out on 36 trees during the "May - October" growing seasons in 2017 and 2018. Results. The main regularities in the seasonal dynamics of the EI and capacitance characteristics of PTC of old-aged Scots pine trunks were the same over the two observation seasons. Differences in dynamics from one year to another appear as changes in the timing of their individual stages and can be explained by peculiarities of weather conditions in a specific year. Regularities in the seasonal dynamics of low- and high-frequency impedance exhibit similar trends: the values of these characteristics decline with the end of the dormant state in spring, remain relatively low during summer, and rise upon passage to winter dormancy in autumn. The seasonal dynamics of electrical capacitance of the trunk PCT is characterized by increasing values when the growth processes are activated in the "spring-early summer" period and by decreasing values at the stage of growth termination and passage to winter dormancy in autumn. EI and electrical capacitance measurements provide additional information about the timing and intensity of the processes that occur in PCT of the trunk and relate to the tree growth, tissue differentiation, and adaptation to seasonal changes in environmental conditions. The measurements can be used in comprehensive diagnostics of the vital state of trees. The best time for diagnostic measurements and monitoring observations is August. If the measurements are performed at another time period, seasonal peculiarities of the dynamics of measured values should be taken into consideration. Conclusion. The trends related to changes in values of low- and high-frequency impedance, as well as electric capacitance, are similar to known regularities and consistent with the timing of the growth-associated anatomical and physiological processes in PCT of conifer tree trunks.