Water Sources Of Desert Plants In Eastern Qaidam Basin

Arid and semiarid areas are occupied one-third of the total global land, and vegetation is very important for relieving and improving ecological crisis in arid and semiarid areas. However, plant growth is often limited by available water supplies in these regions. Understanding water sources and water use patterns of desert plants is helpful to improve eco-environment of arid and semiarid areas. Different plants absorb water from different sources. When the plant water sources reduce, the distribution regions of vegetation will accordingly decrease. So, the research of plant water sources will help us to know the spatial and temporal patterns and dynamics of plants under the background of global change.We choose Golmud and Delingha as our study areas, Golmud locates in the south of Qaidam basin, and Delingha locates in the northeast. By means of stable hydrogen and oxygen isotopes analysis, this research studied the water sources of desert plants and compared the water sources in different plants and different seasons in Golmud and Delingha. Besides, in order to improve the understanding of water use strategies of desert plants and supply scientific basis for maintaining desert ecosystem stability and resuming the damaged ecosystems, the relationship between soil water content and precipitation was used to describe the percentages of different plant water sources.Soil water content of sample plot in Delingha is higher than Golmud. In Delingha plot, biological crust appeared on soil surface, clay particle in surface soil mechanical composition had a high level, therefore, the surface soil water content in Delingha plot is the largest; Soil water content of 50-70cm in Golmud plot is the highest.δ18O values of soil water in all soil layers from two sample plots have similar results and show no obvious isotopic gradient.The slopes and intercepts of Meteoric water line of Golmud plot and Delingha plot are lower than the global, but the intercept of Golmud plot is only -4.566, indicating the extremely arid climate condition. Golmud area is the northern border of Qinghai-Tibet Plateau where the southwest monsoon can reach. In early July, the water vapor sources of precipitation in Golmud plot are mainly from the evaporation of local rivers and lakes, from mid-July to early September, the water vapor sources of precipitation are mainly from Indian Ocean. From late June to early September, the water vapors of precipitation in Delingha plot are mainly from local evaporation. In late September, the water vapors of precipitation in Golmud plot and Delingha plot are both mainly from the local evaporation and Center Asia.Under the prerequisite that precipitation, river water, groundwater and soil water are relatively independent, we calculate the plant water sources of the whole growing seasons and each sampling time in growing seasons. The research results show that, in the whole growing season, five types of desert plants can be divided into two groups based on the differences of water use patterns:the first group includes Ceratoides lateens, Ephedra sinica and Calligonum mongolicum, they mainly use all available water sources, Kalidium gracile and Sympegma regelii belong to the second group, and soil water is their dominant water source.The main water sources of plants in Golmud plot and Delingha plot are both soil water. Because the groundwater table is low in the two areas, groundwater makes a little contribution of water to plants. Therefore, the water utilization strategy of plants in the east of Qaidam basin does not depend on the deep roots of plants to absorb the groundwater, but depend on the developed lateral roots to absorb the near around soil water. The river is also one of the main water sources of plants in the two areas. The main function of precipitation is recharge of soil water.Sympegma is the mutual specie in Golmud plot and Delingha plot, though the precipitations in the two areas are different, the soil water is considered as the main water sources of plants, but the degree is different. In Golmud plot, the plants can use all layers of soil water, but in Delingha plot, the plants only use the surface soil water. In addition, the precipitation of Delingha plot is higher than Golmud plot, and water source of Sympegma in Delingha plot use more precipitation than Golmud plot.The precipitation of Golmud plot is very few, and water sources of Sympegma depend on the developed lateral roots to use the water of all soil layers and the surface runoff nearby.