Abstract: [Objective] In order to provide reference and theoretical basis for vegetation construction in Beijing mountain areas, this study investigated water utilization of typical arbors of Platycladus orientalis and Quercus variabilis in Beijing mountainous area. [Method] We measured stable isotopic values of hydrogen and oxygen of water in the xylem and different water sources by using multi-source linear mixed models (Iso-Source). In combination with the thermal dissipation probe measurement (TDP), we analyzed the contribution rate and amount of different water sources to the two tree species. [Result] Results show that: 1) in dry and rain period, the sap fluid flux was in the order of: P. orientalis in dry period (5.87 kg) < Q. variabilis in dry period (9.42 kg) < P. orientalis in rain period (13.42 kg) < Q. variabilis in rain period (18.26 kg). 2) P. orientalis up-took water from 60-80 cm soil layer and underground water in the dry season, and the contribution rate was 19.8% and 51.4%, respectively, and the average daily use rate was 1.16 kg and 1.16 kg. In the rainy season, P. orientalis consumed top layer (0-20 cm) soil water and groundwater, and the utilization rate was 51.4% and 27.7%, respectively, and the average daily use was 6.90 kg and 3.72 kg. 3) Q. variabilis up-took water from 0-20 cm and 60-80 cm soil layers in dry period, and the utilization rate of 53.5% and 20.2%, respectively, and the average daily use was 5.04 kg and 1.9 kg. In the rainy season time, Q. variabilis up-took water from 0-20 cm soil layer and shallow underground water, and the utilization rate was 51.8% and 38.1%, respectively, and the average daily use was 9.46 kg and 6.96 kg. [Conclusion] In terms of the water use characteristics of P. orientalis and Q. variabilis, two species had similar utilization of water source depth. Thus in afforestation, the two species should not be mixed together to avoid competition for water sources. In Beijing mountainous area with seasonal drought, less water consumption species of P. orientalis should be selected for afforestation.

Key words: Platycladus orientalis, Quercus variabilis, water source, the stable hydrogen and oxygen isotopes