Study On Water Sources Of Populus Euphratica Based On The Stable Isotope Techniques In Desert Riparian Forest

Populus euphratica is constructive species in desert of natural distribution. It maintains theecological balance of distribution area to protect oasis agricultural production, its charactersincluding salt-tolerant, maintaining water, anti-drought, and anti-sand, which leads to higherecological, economic and social value. In recent decades, the area of natural P. euphraticacommunity in Ejina natural oasis has reduced sharply as the results of sharp decrease in theamount of regional water, climate change and vandalism. So it is of utmost importance toformulate the conservation strategy of P. euphratica. This study discussed the contributions ofdifferent potential water sources and the mean depth of water uptake of different ages of P.euphratica, the response of rainfall pulsation for different ages of P. euphratica, based on thecomposition of the stable oxygen and hydrogen isotope (δ18O,δD) of the xylem in different ages ofP. euphratica and different potential water sources, combined with the change of soil watercontent, the intention is to explain water use characteristics of different ages of P. euphratica inthe lower reaches of the Hei River. The results showed：The water utilization of different ages of P. euphratica came from different sources. Theseedlings of P. euphratica mainly used the soil water in30~50cm layers, with the utilization rateof70%, while the utilization rate of groundwater only about6%. The mature tree of P. euphraticamainly used the soil water in200~320cm layers and the groundwater, with the largest utilizationrate at85%of the groundwater. The over-mature tree of P. euphratica mainly used the soil waterin100~260cm layers and also the groundwater, with the higher utilization rate (about96%) of thegroundwater. And the depth range of the over-mature tree is wider than seedlings and mature treeof P. euphratica.The mean depth of water uptake of different ages of P. euphratica came from different soildepth, its selective use soil moisture of different depths with the changes of its age. The meandepth of water uptake of the seedlings of P. euphratica was37cm. The mature tree of P.euphratica mainly absorbed soil depth in170~182cm layers, the mean depth of water uptake was145cm. The over-mature tree of P. euphratica mainly absorbed soil depth in104~112cm layers,the mean depth of water uptake was149.5cm. And the depth range of the over-mature wood andmature tree is wider than seedlings of P. euphratica.Water source absorption ratio changes greatly of young P. euphratica in the rain before and afterrain. Before rain, the main absorption of0~30cm of soil water, using the proportion is as high as88~90%, the mean value of89.9%, only2.9%of the use of groundwater. After the rain, the useof precipitation of up to60%, the mean value of19%. The main water sources of mature P.euphratica were groundwater and deep subsoil water. The depth range of the mature P. euphraticais wider than young P. euphratica.The main water source is not changes regularly from different distance of the river bank ofdifferent ages of P. euphratica. The main use of deep soil water and groundwater. from the riverbank5m P. euphratica mainly used the soil water about100cm layers, with the largest utilizationrate at85%,and the largest utilization rate at64%of the river.The P. euphratica from the river bank20m mainly used the soil water in200~300cm layers,with the largest utilization rate at88%,and the largest utilization rate at64%of the river, to otherlayers utilization rate is very low, and the use of the river is almost zero.The P. euphratica from the river bank100m,500m, and1000m main water resource from thesoil water about150cm,150cm, and70cm layers respectively, with the largest utilization rateseparately at78%,78%,and86%.