Andrea Foetzki

Water relation characteristics ofAlhagi sparsifolia and consequences for a sustainable management

Water relation characteristics of the desert legumeAlhagi sparsifolia were investigated during the vegetation period from April to September 1999 in the foreland of Qira oasis at the southern fringe of the Taklamakan Desert, Xinjiang Uygur Autonomous Region of China. The seasonal variation of predawn water potentials and of diurnal water potential indicated thatAlhagi plants were well water supplied over the entire vegetation period. Decreasing values in the summer months were probably attributed to increasing temperatures and irradiation and therefore a higher evapotranspirative demand. Data from pressure-volume analysis confirmed thatAlhagi plants were not drought stressed and xylem sap flow measurements indicated thatAlhagi plants used large amounts of water during the summer months. Flood irrigation had no influence on water relations inAlhagi probably becauseAlhagi plants produced only few fine roots in the upper soil layers. The data indicate thatAlhagi sparsifolia is a drought-avoiding species that utilizes ground water by a deep roots system, which is the key characteristic to adjust the hyper-arid environment. Because growth and survival ofAlhagi depends on ground water supply, it is important that variations of ground water depth are kept to a minimum. The study will provide a theoretical basis for the restoration and management of natural vegetation around oasis in arid regions.

Contributions to a Sustainable Management of the Indigenous Vegetation in the Foreland of Cele Oasis — A Project Report from the Taklamakan Desert

The ecological situation of oases at the southern border of the Taklamakan desert is shortly described, and the importance of a vegetation from indigenous species at the transition from the oases to the desert is emphasized. This vegetation serves as a shelter against sand drift and as a source of livestock feed as well as of fuel and construction material. Its destruction through overexploitation and other interventions during the last decades has considerably promoted sand drift and the deterioration of arable land. Therefore, a management of this protective vegetation is to be developped that leads to a sufficient regeneration and that ensures both its preservation and its use. A research project that is carried through jointly by Chinese and European scientists shall yield an ecological basis for this sustainable management.

Comparative study on the water characteristics of Populus euphratica with different depths of underground water in the foreland of Takelamakan Desert

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.

Water relation characteristics of Calligonum and consequences for a sustainable management of vegetation in the southern fringe of Takelamakan Desert

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.