The effect of depth to ground water on water relations of obligate phreatophyte Populus euphratica (Salicaceae) was investigated in the foreland of the hyper-arid Takelamakan Desert in Xinjiang, NW China. P. euphratica grow on sand dunes of different height (0--15.4m) above ground water that was the only water source for the species. The depth to ground water from the surface of the lowest sand dune was 6.8m under Populus. The water relation data illustrated the negative impact of sand dune height on water status of the species. Predawn and midday water potentials decreased significantly with increasing sand dune height. Water relation data suggest that decreases in hydraulic conductance with increasing distance to ground water have caused decreases in stomatal conductance due to a diminished water supply in plants on higher sand dunes. Results of this study indicate that whole-tree hydraulic conductance for Populus is heavily influenced by below ground hydraulic conductance. Whether the variations in hydraulic conductance are a function of increased path length or if they are the result of morphological changes in the conducting tissues remains further investigation. A detailed knowledge of hydraulic parameters in the root system is required to assess the effects of hydraulic limitations on plant water relations.
A successful effectiveness to prevent the oasis from the desertification had been obtained by means of the method to establish the man-made vegetation in the south fringe of Takelamagan Desert since the middle of 80’s last century. This paper generalizes the characteristics of Calligonum and summarizes the ways to establish it (seedling, cutting and sowing) and main technical points of every ways. In the meantime, it also clarifies the strategy to select the different ways.
On field sites, water physiological characteristics of the desert legume Calligonum were investigated during the vegetation period in 1999(2000) in the southern fringe of the Takelamakan Desert, Xinjiang, NW China. The seasonal variation of predawn water potentials and of diurnal water potential indicated that Calligonum plants were well water supplied and it has stronger ability to maintain the water balance within the body over the entire vegetation period. Water relationship parameters from pressure-volume analysis confirmed that Calligonum plants were not drought stressed and xylem sap flow measurements further indicated that Calligonum plants were well water supplied during the summer months. The data indicate that artificial flooding only had limited effects on the water relations of plant. Long-term adjustment to the hyper-arid environment and its growth (survival) of Calligonum maybe is dependent on permanent contact with ground water. Therefore, it is important that variations of ground water depth are kept to a minimum. The study will provide theoretical basis for the restoration and management of natural vegetation in arid and semi-arid regions.
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