# Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree
## 5 Conclusions  
A TPAM system was developed to remotely, continuously, and quantitatively monitor the physiological activity of trees. The developed TPAM system also measures the ambient temperature and light intensity and wirelessly transmits the measured data to the hub system through ZigBee communication. Previous studies using plant electrical impedance measurements have used a two-contact measurement method, which includes errors due to the contact impedance of the electrodes. To improve the error of the two-contact measurement method, the TPAM system adopted a four-contact measurement method and measured the impedance of the trees according to seasonal changes over a long period of time. The impedance of the tree showed a periodic fluctuation cycle on a daily basis in the short term and tended to increase as the season changed from summer to winter in the long term. The shape of the impedance changes on a daily basis showed a shape that reversed the change in the ambient temperature. Even in winter, when there were no tree leaves, fluctuations in the tree impedance were observed according to the daily temperature changes. Since the absence of leaves means that the tree's physiological activity is at its lowest, the daily impedance fluctuations at this time are presumed to be a direct effect of ambient temperature fluctuations that are unrelated to the tree's physiological activity. The direct impact of these temperature fluctuations on tree impedance fluctuations will also affect the presence of tree leaves. Excluding the influence of temperature, the impedance values at constant temperatures of 15 degrees, 20 degrees, and 25 degrees were analyzed to determine the relationship between the impedance and physiological activity of the tree. As a result of analyzing the impedance value when the temperature was 25 degrees every day, it was found that the impedance value increased linearly with a slope of 8.4 \(\Omega\)/day from summer to winter. The conclusion from this series of analyses is that in order to understand the physiological activities of trees, it is important to exclude the influence of temperature by continuously measuring the ambient temperature as well as measuring the impedance. In the future, the following additional monitoring and system supplementation work will be needed. This paper reports monitoring results for the period from summer to early winter, but monitoring should also be performed for the period from late winter to spring and summer. The monitoring of multiple individuals of the same breed is necessary, as well as the monitoring of different breeds using the TPAM system. Additionally, the TPAM system must be equipped with a humidity measurement function. It is also necessary to examine whether humidity is related to tree growth and physiological activity. Currently, the system is constructed using commercial parts, resulting in high power consumption. Figure 16: Correlation between light intensity and impedance at a specific date. Because the measurements must be performed over several months, TPAM systems require low power consumption. An application-specific integrated circuit (ASIC) that can achieve a low power consumption are currently under development. J.K. produced HW. [PERSON] performed FW and SW coding, measurements, data processing, and drafted the paper. J.P.K. contributed to funding, paper idea, research progress, paper organization, and paper modification. All authors have read and agreed to the published version of the manuscript. This paper was supported by the Education and Research promotion program of KOREATECH in 2023. This paper was supported by the Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0008458, The Competency Development Program for Industry Specialist, 2023). Not applicable. The data presented in this paper are available from the corresponding author on reasonable request. The authors thank the Cooperative Equipment Center at KOREATECH for assistance with FE-SEM analysis.