Comparing water uptake patterns of two tree species using stable isotopes on the Loess Plateau, China

Abstract The water consumption mechanism of plantations is important to understand for the selection of afforestation tree species and sustainable watershed management in semi‐arid regions. In this study, Robinia pseudoacacia and Pinus tabuliformis , which are commonly planted on the Loess Plateau of China, were selected to investigate the possible difference in water uptake modes. In 2019–2020, the stable isotopic compositions (δ 2 H, δ 18 O) of precipitation and the xylem and soil water of these two trees were sampled and compared using the direct inference approach and MixSIAR model. The difference in soil moisture was also measured. The results showed that the δ 18 O content of surface soil water (0–40 cm) was closely related to precipitation, while that of deep soil layers (100–200 cm) remained stable. The MixSIAR model performed appropriately in quantifying water apportionment, especially in the drought year of 2019. In July–August 2019, R. pseudoacacia showed strong drought resilience by absorbing water from the deep soil. The 0–40 cm and 100–200 cm soil layers contributed 0.325 and 0.376 to water absorption of R. pseudoacacia , and 0.675 and 0.151 to that of P. tabuliformis , respectively. However, there was a minor difference in the soil water uptake modes between the two species in the humid year of 2020. Compared with P. tabuliformis, R. pseudoacacia increased its consumption of water by 9.9% and 25.1% in the drought and humid year, respectively, which indicated that R. pseudoacacia plantations may contributed to drier deep soil layers. This study helps to improve our understanding of the water uptake mechanisms of common afforestation tree species on the Loess Plateau.