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1. Climatic data: The precipitation and temperatire of 2019 and 1980-2018 were obtained from the local meteorological station.

2. Stable isotope data (δ²H and δ¹⁸O): The calculation of isotopic ratios was expressed as: δ²H = (R_sample – R_standard) – 1, δ¹⁸O = (R_sample – R_standard) – 1, where R_sample and R_standard are the ²H/¹H and ¹⁸O/¹⁶O molar abundance ratios of the samples and the standard (V-SMOW, Standard Mean Ocean Water), respectively.

3. Volumertic soil water content: Soil samples were collected randomly at layers of 0-10, 10-20, 20-30, 30-50, 50-70 and 70-100 cm using a cutting ring (height is 5 cm, volume is 100 cm³) with three replicates after removing any rocks and litter during the experimental period. After collecting the soil samples, the fresh weight (FW) was measured immediately, and the samples were then taken to the laboratory and oven dried at 105 °C to a constant weight to measure the dry weight (DW). The soil water content (SWC) was calculated as: SWC = 100 * (FW - DW)/DW. The soil bulk density (SBD) was calculated as: SBD (g/cm³) = DW/100. The soil water content was converted into the volumetric soil water content by multiplying it by the soil bulk density.

4. Root (Fine root) biomass fraction: Root (Fine root) biomass in different soil depth/ Total root (fine root) biomass in all soil depth.

5. Fraction of water use: We used IsoSource stable isotope mixing mode (http://www.epa.gov/wed/pages/models/stable-Isotopes/isosource/isosource.htm) to quantitatively determine the proportional contribution of each of the water sources to the plant xylem water. Two parameters needed to be input before running the model. One was the source increment, which is generally set as 1%; the other was the mass balance tolerance, which is generally defined as 0.1‰.

6. Proportional similarity: The proportional similarity is the hydrological niche overlap between coexisting species was calculated with fraction of water use.