| Through monitoring simultaneously three physiological indexes including stem flux rate, stem diameter variations and leaf water potential of five kinds of desert plants growing in the lower reaches of Tarim River, which are, Lycium ruthenicum, Alhagi sparsifolia, Poacynum hendersonii, Karelinia caspia and Hexinia polydichotoma and the environmental factors including air temperature, air relative humidity, solar radiation, soil moisture, wind speed and soil water potential using a Phytalk phytomonitor system which was produced by PhyTech Company in Israel and a PSYPRO water dew point instrument which was produced by WESCOR Company in the USA. This thesis systematically analyzes diurnal variation of the three indexes and establishes the mathematics reaction model of them to environmental factors by stepwise recreation analysis. At the same time, measure the value ofδ13C of different plants, and analyze the relationship between stem flux rate, leaf water potential, the variation of stem diameter and the value ofδ13C. Through the analysis of variance and multiple comparisons on the physiological indicators reveals the difference in water physiological ecological characteristics and self-maintaining property. The main results showed:Change trends of the day process of the stem flux rate in these plants are showing remarkable day and night rhythms, while this fluctuation in day is more evident than in night. The main environmental factors affecting the stem flux rate of these plants are solar total radiation, air temperature, soil moisture and wind speed. The day process of stem diameter variations has obvious day and night variation law, which shows that there is shrinking in the day and swelling in the night. The stem diameter variation is mainly affected by factors of soil humidity, solar radiation, air temperature, air relative humidity and wind speed. The water potential of all species is high in the early morning, keep a low value after sunrise, and increase in the afternoon. Leaf water potential is negative correlative with solar radiation and air temperature; is positive correlative with soil moisture, soil water potential and relative humidity in the air.Except Lycium ruthenicum, the relationship of leaf water and stem flux rate in other four kinds of plants are significantly or very significantly correlated. The variation of stem diameter is increasing with the decreasing of the sap flow. The diurnal variation of shrinkage of stem diameter has a very good correlation with leaf water potential, which was advanced the shrinkage of stem diameter. The carbon isotope composition and leaf water potential of these species have a linear and negative correlation. The mean stem flux rate of different species are different, Karelinia caspia>Hexinia polydichotoma>Alhagi sparsifolia>Poacynum hendersonii>Lycium ruthenicum. The relative shrinkage of stem diameter of these plants descending order as: Lycium ruthenicum>Karelinia caspia>Poacynum hendersonii>Alhagi sparsifolia>Hexinia polydichotoma. The order of long-term water use efficiency of these species is: Lycium ruthenicum>Alhagi sparsifolia>Poacynum hendersonii>Karelinia caspia> Hexinia polydichotoma. The order of value of leaf water potential of these species is: Hexinia polydichotoma>Karelinia caspia>Poacynum hendersonii>Alhagi sparsifolia>Lycium ruthenicum. The soil-plant ratio of water potential gradient is: Lycium ruthenicum> Alhagi sparsifolia> Poacynum hendersonii> Karelinia caspia> Hexinia polydichotoma. The plant-atmosphere ratio of water potential gradient is: Karelinia caspia>Hexinia polydichotoma>Poacynum hendersonii>Lycium ruthenicum>Alhagi sparsifolia.The self-maintaining ability of Lycium ruthenicum and Alhagi sparsifolia are the most strength among the five test plant species, the ability of Poacynum hendersonii and Karelinia caspica are the in the middle among the five test plant species and the ability of Hexinia polydichotoma is the weakest among the five test plant species.
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