Decrease of Leaf Water Potential and Leaf Injury of Tea Plant (Thea sinensis L.) Subject to Cold Winter Wind in Sanin Region of Japan

In the previous report4), we indicated that cold wind injury of tea leaf in Sanin region occurred under decreases of leaf water potential (ΨL) caused by low temperature and strong wind. We attempted to clarify why ΨL decreases under the environments and tried to simulate the cold wind injury under artificial condition in order to know whether decrease of truly causes leaf injury. Under a combination of low soil and air temperature (0.5/–1.5-C) with strong wind (4.5ms-1), ΨL decreased to –0.6MPa under a dark condition and to –1.8MPa under a light condition. Leaf injury appeared under the light condition. Water flow resistance (R) inside the plant increased when low soil and air temperature (0.5/–1.5-C) was maintained under changing wind speed below the light condition. R in leaf and roots increased with decreased plant body temperature when R of the parts was directly assumed by the slope between pressurization rate with a pressure chamber and water flow rate through the plant parts under several temperatures. We concluded that the cold wind injury in Sanin region may be caused by decrease of leaf water potential because low soil and air temperature drastically increase water flow resistance inside the leaf or the roots, and strong wind and short wave radiation accelerates transpiration rate.