Abstract: Based on the measurement of the stable isotope ratios of hydrogen and oxygen in soil, fog, rain, and plant non-photosynthetic tissues, as well as the gravimetric soil water content, soil water potential, and leaf water potential, this paper studied the water use strategy of F. tinctoria at its different life stages in Xishuangbanna of Southwestern China. The water potential in shallow soil layer (10-50 cm) had a greater change between hot-dry season and foggy season, whereas that in deeper soil layer (51-120 cm) had less change during the seasons. No significant difference was observed in the soil water content between foggy season and hot-dry season. The leaf water potential at predawn and midday varied with life stage. From the measurement of the stable isotope ratios and other parameters, it was found that shallow soil water was the main water source for F. tinctoria, and F. tinctoria had different water use strategy at its different life stages.

Key words: stable isotope, water use strategy, soil water potential, leaf water potential, Ficus tinctoria,  , Xishuangbanna, winter wheat sowing in spring,  , spike differentiation stage, physiological indices, grain yield, cold tolerance, principal component analysis.