Water Source Change of Platycladus orientalis under Different Water Regimes in Beijing Mountainous Area: a Multi-timescale Study

【Objective】This study aims to explore the responses of water resources of Platycladus orientalis to various water conditions, so as to provide scientific support for managing P. orientalis plantations in Beijing mountainous area. 【Method】 P. orientalis, a typical afforestation species in Beijing mountainous area, was used as the study object. Three consecutive years with different annual precipitation were targeted to analyze the water source characteristics of P. orientalis under different annual precipitation conditions, and the annual precipitation in 2015, 2016, and 2017 was 580 mm, 649.8 mm, and 309.3 mm, respectively. The stable hydrogen and oxygen isotope technique, and MixSIAR model were used to analyze water resources. Simultaneously the climate data were collected, and the soil water content in the plot was measured, and the relative extractable water (REW) of soil was calculated. All the data were used to analyze the water use patterns of P. orientalis under different water conditions. 【Result】 1) The REW of deep soil was significantly higher than that of shallow soil (P<0.05), and rainfall significantly increased the REW of each layer. REW in rainy season is significantly higher than that in dry season. In the three years, the REW of shallow soil in 2016 (0.341) and 2017 (0.360) was significantly lower than that in 2015 (0.423) (P<0.05), while the REW of deep soil in the three years was not significantly different, which was 0.613, 0.618 and 0.587 in chronological order. 2) The contribution rate of deep soil water was generally greater than that of shallow soil water, but the contribution rate of shallow soil water increased after rain, with 45.7% after rain and 44.5% without rain, respectively. In different seasons, P. orientalis had higher utilization of deep soil water in the rainy season (56.2%) than in the dry season (54.8%). In different years, the utilization of the deep layer in dry year (2017) was 57.8%, and was significantly higher than that in normal year (2015) (54.1%) and rainy year (2016) (54.6%). 【Conclusion】 P. orientalis mainly relies on deep soil water to maintain its water demand. Rainfall events and seasonal soil water variation do not significantly affect the water use strategy of P. orientalis, but the significant decrease in annual rainfall will cause P. orientalis to be more dependent on deep soil water. © 2022, Editorial Department of Scientia Silvae Sinicae. All right reserved.