[Water utilization strategy of three soil and water conservation trees on Ordos Plateau, China]

To understand the adaptive strategies of three tree species used for soil and water conservation in the hilly area of eastern Ordos Plateau, Hippophae rhamnoides, Pinus tabuliformis and Armeniaca sibirica, we measured the δ¹⁸O value of xylem water of branch and potential water sources and the δ¹³C value of leaves, and analyzed the relative contribution of each potential water sources to different tree species by multiple linear mixing model. We further compared the seasonal dynamic and inter-specific variation of water source and water use efficiency (WUE). The results showed that H. rhamnoides, P. tabuliformis and A. sibirica mainly used soil water in 10 cm layer in May, accounting for 88.5%, 94.0% and 91.6% of their total water uptake, respectively. In July, H. rhamnoides mainly used soil water in 10-25 cm layer (44.6%) and rain water (35.4%), P. tabuli-formis mainly used rain water (93.7%), and A. sibirica mainly used soil water in 25-100 cm layer (55.9%) and rain water (36.8%). In September, H. rhamnoides mainly used soil water in 25 cm and 75-100 cm layers (88.9%), P. tabuliformis mainly used soil water in 10 cm and 50-75 cm layers (84.5%), and A. sibirica used that in 10-100 cm layer. WUE of H. rhamnoides in May was significantly higher than that in July and September. WUE of P. tabuliformis in July was significantly higher than that in September. WUE of H. rhamnoides was significantly higher than that of P. tabuliformis and A. sibirica in May and July. Three tree species use different depths of soil water or rainwater based on their availability in different seasons. H. rhamnoides and P. tabuliformis could improve their WUE to adapt to environmental change under drought, which might be more suitable for local semi-arid environment than A. sibirica.