Long term field measurement of xylem potential in tea plants - relation of potential change with environmental factor

摘要

Non-destructive and real-time monitoring of the physiological state of woody plants such as fruits and tea are desirable for rational cultivation based on the planting conditions. The purpose of this study is to develop a monitoring system for planting conditions in a field by the measuring xylem potential and analyzing the relationship between the potential changes and environmental factors. A tea plant (Camellia sinensis (L.) O. Kuntze) pruned in the middle of March was used for this experiment. To measure the xylem potential, an injection needle connected with a silicone tube and a reservoir filled with 10mM KC1 was inserted into the xylem apoplast. The reservoir was connected to the other reservoir contained 3M KCl through salt bridge. Unpolarizable Ag/AgCl electrode was dipped in 3M KCl-filled reservoir. By this liquid junction system, the long-time recordings over years were succeeded in the field. The highest period of the xylem potential coincided with the dormancy. The xylem potential has clearly repeated the diurnal changes in the positive shift gradually after dawn and a negative shift after late noon throughout the recording periods except for summer. During the summer (late in May to end of August), diurnal change in the xylem potential has showed a completely opposed tendency. These two diurnal changes were changeable by the changes of the light and temperature conditions in a controlled room. When it rained, these diurnal changes disappeared. The xylem potential showed a rapid negative shift at the rainfall and slow recovery at the initial level after the rainfall ended.