Keywords: 
• forest ecology /
• stable isotopic composition of atmospheric water vapor /
• forest ecosystem /
• influencing factors /
• relativity /
• Mount Tianmu

Abstract: Stable isotope techniques, one of the most effective techniques for understanding carbon and water relationships in terrestrial ecosystems, are commonly used domestically in agricultural but not in forest ecosystems. To establish long-term continuous observations with flux towers in forest ecosystems and to reveal stable isotopic composition of atmospheric water vapor for regional characteristics in ecosystem water balance research, a subtropical evergreen and deciduous broadleaf mixed forest observation tower was established for Mount Tianmu in Zhejiang Province. The tower detected hydrogen and oxygen isotopes and had an in situ measurement system based on Tunable Diode Laser Absorption Spectroscopy （TDLAS）. Also multi-layer gradients for temperature and humidity, wind speed, and radiation using conventional meteorological instruments were operational from December 2012 onward. Based on data observed from August to September 2013, the stable isotope composition of atmospheric water vapor influencing factors and their relationships were analyzed. Results showed that atmospheric rainfall, air temperature, soil temperature at 5 cm soil depth were important environmental factors in the forest ecosystem in Mount Tianmu; the air temperature and water vapor stable isotope composition were fitted in a linear relationship, while the soil temperature at 5 cm soil depth were fitted in a polynomial relationship with water vapor stable isotope composition, and also the statistics showed that the correlation was admirable. Thus, compared to agricultural ecosystems, water vapor stable isotope composition factors in this forest ecosystem had little influence.［Ch, 13 fig. 17 ref.]