Contrasting water sources of evergreen and deciduous tree species in rocky mountain area of Beijing, China

- Selected tree species are important afforestation species in the Beijing area.
- Stable isotope analysis can ascertain water sources for the studied tree species.
- Comparing tree water sources provides an insight into species' drought adaptability.

Trees growing in the Beijing mountain area are often located on rocky outcrops. As water sources for these trees are poorly understood, we investigated seasonal water sources of four typical tree species (Platycladus orientalis, Pinus tabuliformis, Robinia pseudoacacia and Quercus variabilis) using stable hydrogen and oxygen isotope methods in this area. Results indicate that P. orientalis predominantly utilized water from natural springs (57.8%) during the dry season and uptake water from shallow layer (0- 20 cm, 78.4%) during the wet season. P. tabuliformis predominantly utilized shallow (46.8% and 37.7%, respectively) and deep (60- 100 cm, 24.9% and 27.6%, respectively) soil water in the dry and wet seasons. R. pseudoacacia mainly absorbed shallow soil layers water (54.3%) during the dry season and switched its water source to all of the soil layers (19.2- 30.9%) during the wet season. Q. variabilis predominantly extracted water from the shallow (29.8%) and middle (20- 60 cm, 38.6%) soil layers during the dry season; and it primarily relied on middle layer soil water (25.9%) and natural springs (40.5%) in the wet season. These four tree species showed a strong adaptation to drought periods and our findings provide valuable information which can be used when selecting tree species and planning long-term ecological management of afforestation around the Beijing mountain area.