Diurnal and Seasonal Changes in Stem Water Content of Single Yulan Magmolia Tree

In this paper the objective was to study diurnal and seasonal changes in Yulan Magmolia tree by SWR principle. Laboratory and field tests were performed. Laboratory calibration test was performed on two sapwood samples, which shows that the relation between the volumetric water content and the output voltage of SWR sensor was monotonic as the coefficients R

2

reached above 0.90.were periodically weighed on a balance. In field test, the diurnal and seasonal changes were monitored in natural Yulan Magmolia tree by SWR sensor for nearly 2 years. It indicated that seasonal variation of stem water content measured was 20% ~ 25%. A maximum in stem water content occurred in summer, then decreased in autumn, and reaching a minimum in winter, recovery is almost complete till next spring. The short-term (diurnal) variations were found 2% ~ 5%. The daily changes show that a decline in stem water content happened, and then recovered each day. At the same time, leaf water content and sap flow velocity were measured, which shows that diurnal leaf water potential has the similar curve with diurnal stem water content while sap flow velocity was reverse to stem water content.