Long-term study on the seasonal water uptake of Platycladus orientalis in the Beijing mountain area, northern China

•Water uptake pattern of Platycladus orientalis is proposed based on long-term study in the rocky mountain areas of North China.•The P.orientalis prefer to use water from upper soil layers (0-40cm) throughout the year.•The groundwater could become the dominant water source for P.orientalis during the extremely dry season.•The P.orientalis water uptake has a great plasticity. Understanding how extreme drought and precipitation influence the water uptake patterns of vegetation is essential to assessing the responses of vegetation to climate change and evaluating regional water security. We introduced stable hydrogen and oxygen isotopes to determine the seasonal pattern of water uptake by the evergreen coniferous species Platycladus orientalis from June 2011 to June 2014 in the semiarid rocky areas of North China with shallow soil. Temporal variations in the soil water content (SWC), transpiration and root distribution were examined to analyze the key role of groundwater in plant water sources during the extreme drought. Platycladus orientalis showed great dependence on the surface soil water (0–20 cm) and a water uptake proportion greater than 50% in all rainy seasons (June–September) was observed. Our study also revealed that P.orientalis preferred to use upper soil moisture (0–40 cm) in the dry seasons as long as the supply met the demand, and it would turn to deep soil water and groundwater under dramatic reduction in the surface soil water content. During prolonged extreme drought, groundwater use increased from 25.3% in the early period to 61.3% in the late period. These findings suggest that P. orientalis water uptake has great plasticity and that its water uptake depth varies with a decline in soil water. In addition, a long extreme drought period will lead to a preference for and an increase in groundwater use, which means that P. orientalis can adapt well to extreme climates.