Abstract: The ecological restoration applicability of plant species is of great significance to the selection of greening species. Based on hydrogen and oxygen stable isotope technique, we qualitatively analyzed the differences of water sources in growing season between two Caragana species (C. stenophylla and C. korshinskii) in similar habitats in the South Mountains of Lanzhou by using direct comparison method and Bayesian mixing models (MixSIAR). The results showed that the two species of Caragana have multiple water-absorbing layers and are non-single water source plants. The main water absorbing layer of C. stenophylla varied across different months in growing season. Except for September, the main water source of C. korshinskii was the medium-deep aquifers (70-130 cm), which contributed to more than 80%. C. stenophylla preferred to use surface soil water (0-30 cm) after rainfall, but C. korshinskii was not sensitive to rainfall. The main water absorbing layer of C. korshinskii was relatively stable. C. stenophylla can change the main absorbent layer in response to drought stress, indicating a more flexible strategy and strong ability to adapt to drought. Therefore, C. stenophylla has better applicability for ecological restoration.

Key words: Lanzhou City, hydrogen and oxygen isotopes, direct comparison method, MixSIAR, Caragana stenophylla, Caragana korshinskii.