Water Status Detection of Satsuma Mandarin (Citrus unshiu Marc.) Trees using an Electrical Impedance Method

Electrical impedance analysis was conducted using 4-year-old potted Satsuma mandarin (cv. Toyofuku-wase) trees to measure tree water status. Two electrodes were inserted to the tee trunk 3 cm apart and 3 mm in depth, and then capacitance and resistance at four frequencies of alternative current (0.1, 1, 10 and 100 kHz) were detected using an LCR meter which was connected to the electrodes. During drought treatments performed in June 2005 and October 2005, transpiration and photosynthesis rates in the leaves and the changes of the tree trunk diameter were simultaneously measured using a portable photosynthesis system and dendrometers, respectively. Resistance at the four frequencies increased as the duration of the drought treatment was longer, on the contrary capacitance, transpiration rate and photosynthesis rate decreased. Tree trunk diameter has daily fluctuated and then dramatically shrank at day 0 in June treatment and day 2 in October treatment. Relationship between parameters of the electrical impedance and other water related parameters was discussed.

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