Abstract:

In the Taklamakan desert region, water is the most important limiting factor to influence plant growth and distribution. The study of water relations is necessary to provide an ecological basis for the sustainable management of the vegetation at the transition between oasis and sandy desert to protect oasis environments. At the same time, the study also provided theory about how to use the limited water resources to regenerate vegetation. In the southern fringe of the Taklamakan desert Calligonum caput-medusae Schrenk (Polygonaceae) is an introduced species which serves as important shelter vegetation against sand drift at the foreland of the oasis. We investigated: 1) the degree to which plants suffered water stress during flooding conditions in summer; 2) the adaptability of physiological characters in water relations to this extreme environment; 3) the effect of irrigation on water status of vegetation (utilizing summer flooding). From April to October in 1999, around the 20th of each month, the predawn water potential (Ψp; between 5∶00 and 6∶00) and the afternoon water potential (Ψ; between 13∶00 and 14∶00) were measured using pressure chambers on six plants with three measurements per plant. Following the measurements of water potential, the pressure and volume (PV) curves from three or four samples were established. The results showed C. caput-medusae kept positive turgor during the growing season. Development of water deficit was not severe and the water stress that plants suffered was still in the normal range. Thus, the water stress induced by drought is not severe enough to threaten the survival of the artificial vegetation. During the growing season, C. caput-medusae still maintained relatively high water potential and osmotic potential as the environmental stress increased. At the same time, no experimental evidence indicated that the accumulation of solute (NsDM) reached high levels either. Therefore, the physiological process of plants still worked in normal conditions. The relative water content (RWCp) always remained high during the growing season, which was helpful to plants to prevent excess water loss in drought environments. Maintaining high level RWCp would be the adaptability of the plant to the extreme environment of the Taklamakan desert. Those adaptabilities of physiological characters exhibited in C. caput-medusae indicated the type of the plant to adapt drought environmental stress is resistance. The drought-adapted physiology of C. caput-medusae at the leaf level was mainly shown in an increase in the proportion of apoplasm, bulk modulus of elasticity (εmax), long standing high relative water content (RWCp), and increased RWCp and WCsat after irrigation. Irrigation in summer by flooding is helpful to recover the water status of C. caput-medusae and is probably one of the important reasons that the vegetation avoids serious water stress.