COMPARATIVE RESEARCH ON THE WATER POTENTIAL AND TRANSPIRATION RATE OF CHINESE PINE PLANTATIONS FROM DIFFERENT PROVENANCES IN BEIJING
油松不同种源在北京地区水势和蒸腾速率的比较研究

The yearly variation water potential and the daily process of tr- anspiration rate of chinese pine(Pinus tabulaeformis)plantations in Beijing,aged 8 years,coming from 13 provenances of 7 climatic eco- types,were determined with presseue-chamber technique and BL8503 porometer.The result showed that for all provenances,the mi- nima of water potential are found in winter(-19.35 bar)and in the period of high temperature and dry seasons(-14.81 bar).There are distinct differences among the values of water potential from diffe- rent provenances,the largest for the provenances of northeastern ecotype and the least for southern ecotype.The value of water po- tential is obviously related to the mortality in winter,the populati- ons originning in south have the lowest water potential and the hi- ghest mortality in winter. The daily and seasonal change of transpiration rate for all pro- venances are apperently regular.The daytime course looks like a convex curve with high value in midday and low value in early mo- rning and night.The curve of yearly course has two peaks.Clear differences are observed among the transpiration rates of different provenances,the northeastern ecotype with the highest value and the southern ecotype with the lowest one.