Study On The Determination Method Of Water Content In Tree Trunks Based On Internal Resistance Of Equivalent Power Source

Water content is an important physiological parameter of standing trees.Common methods for measuring water content in tree trunks in real time are mainly based on the dielectric constant of tree trunks.These methods cannot meet the requirement of plant electrophysiological research because of electromagnetic injections into the trunk,which might disturb biopotential measurements.Electrodes and a tree trunk can form a power source.The internal resistance of the power source has a certain connection with water content in tree trunks.A new method for determining water content in tree trunks in real time may be proposed if the relationship between them is obtained.This method can avoid excitation sources,meeting the requirements of plant electrophysiological research.Moreover,it can reduce power consumption and costs of the measurement system.The diurnal variation of water content in tree trunks of four kinds of standing trees in northern China was studied.Water content in tree trunks and internal resistance of tree-based power source were observed continuously and synchronously,and the relationship model between them was established by mathematical statistical analysis.A method for measuring water content in tree trunks based on internal resistance of equivalent power source was preliminarily proposed.The main conclusions of this paper are as follows:(1)The diurnal variation of water content in tree trunks was observed with four kinds of standing trees: Malus xifu,Eucommia,Purple leaf plum,and Willows.Water content in tree trunks began to decrease continuously at about 12:00.After 16:00,water content showed a trend of gradual increase.Between 22:00 and 2:00 the next day,water content in tree trunks reaches the peak.Subsequently,water content in tree trunks began to decline until after 6:00the next day,the sun rose,the temperature rose,and water content in tree trunks gradually increased.Therefore,sampling at midnight can make the variation range of the water content in tree trunks larger,which provides a basis for obtaining the relationship models between water content in tree trunks and internal resistance of equivalent power source.(2)Water content in tree trunks(y,%)and internal resistance of equivalent power source(x,Ω)of four kinds of standing trees were observed continuously and synchronously.Then,the relationship model between them was established: y = a + b × ln(x),and a and b are related to tree species and other factors.Accordingly,a determination method of water content in tree trunks based on internal resistance of equivalent power source was proposed.(3)The application test was performed on the determination method of water content in tree trunks based on internal resistance of equivalent power source.The relationship model proposed in main conclusion(2)was used to calculate the water content in tree trunks.Take drying method as the reference,the relative errors of the measurement results were between3% and 12%,indicating that the method based on internal resistance of equivalent power may have certain feasibility in the field of detecting the change of water content in tree trunks.