Impedance analysis of Labisia pumila plant water status

Labisia pumila (Kacip fatimah) is a popular medicinal plant in Malaysia. The constituents of this plant have been reported to possess anticancer, antioxidant and anti-inflammatory properties. The growth and production of L. pumila is greatly influenced by the plant water status. Current techniques to measure plant water status are generally based on the plant soil moisture, which apparently did not indicate the real water content inside the plant. There are other techniques to measure directly on the plant such as based on leaf water potential (LWP) and relative water content (RWC). However, these techniques are destructive and time consuming. In this study, four levels of evapotranspiration replacement (ER) treatment which were 100% ER, 75% ER, 50% ER and 25% ER was applied to 30 polybags of L. pumila plants. The plant water status was measured using an impedance spectroscopy technique. A pair of electrocardiogram (ECG) electrode connected to an impedance analyzer board was used to measure the impedance value of the leaf samples non-invasively. Plant water status parameters such as LWP, RWC, volumetric moisture content (VMC), and leaf thickness were measured using standard methods. The results show that after 20weeks of treatment, 25% ER had the highest impedance value ranged from 0.10MΩ to 0.15MΩ at the frequency of 70–100kHz. The resistance of 100% ER at 20weeks of treatment increased from 0.70kΩ to 1.23kΩ as the reactance decreased from 0.51kΩ to 0.28kΩ. Comparatively, the resistance of 25% ER increased from 1kΩ to 1.10kΩ as the reactance decreased from 0.88kΩ to 0.83kΩ. The polynomial regression of impedance measurements with plant water status parameters (VMC, leaf thickness, LWP and RWC) shows that LWP and RWC had the highest R2 (0.78, 0.73). The results show that impedance measurement technique is auspicious to evaluate plant water status.