Abstract: By using auto-data collection system with thermal dissipation sap flow probe,and meteorological,soil and Licor6400 photosynthesis sensors,this paper measured the fluctuations of Acer truncatum sap flow and leaf transpiration in summer and autumn in the West Mountains of Beijing.The fluctuation of sap wood flow was affected by weather.Environmental stress or improvement altered the characters of sap flow wave motion.The daily course of sap flow showed a singlepeaked curve in clear days,i.e.,increased sharply after sunrise,reached the peak around noon,went down then,and reached the valley in next early morning.The starting time of sap flow and the appearing time of valley were 1-4 hours earlier in July than in other months.In June,the sap flow velocity (SFV) of upper trunk was apparently higher than that of middle and lower trunks,whereas in other months,the SFV of lower trunk was higher than that of upper and middle trunks.The difference was 2-3 times in July.Multiple regression analysis showed that SFV was deeply affected by environmental factors,e.g.,air temperature,solar radiation,air humidity,soil temperature and wind speed in the whole growth season,but the main affecting factors were differed with observation period and position,and only atmospheric temperature was always important.The fluctuation of sap flow could better explain the ecological strategy of A.truncatum to drought tolerance.

Key words: Anguilla japonica, High temperature season, Artificially controlling temperature, Maturation induction