Water uptake by coniferous and broad-leaved forest in a rocky mountainous area of northern China

Extreme drought and precipitation are expected to occur more frequently due to climate change, which may influence the water uptake patterns by vegetation in the rocky mountainous area of northern China. In this work, dual stable isotopes were used to detect the water sources of mixed forest of coniferous and broad-leaved tree species and their response of leaf water potential under differently sized precipitation events (no rain: 0.0 mm; light rain: 9.8 mm; moderate rain: 21.8 mm; large rain: 31.6 mm and rainstorm: 51.2 mm). The results showed that Platycladus orientalis and Quercus variabilis had different water use strategies and opposite responses to precipitation. On dry (no rain) days, P. orientalis and Q. variabilis predominantly obtained water from natural springs (43.3% and 36.2%, respectively) and deep soil layer (32.8% and 31.3%, respectively), while Q. variabilis also used water from shallow soil layer (23.4%). Following the rainfall events, the P. orientalis with dense and shallow fine root system absorbed more water from the soil surface layers (23.1-33.5%) and precipitation (15.2-30.7%). The pre-dawn water potential (psi(pd)) and the midday water potential (psi(md)) of P. orientalis increased with the amount of rainfall, revealing a sensitive response to precipitation. On the other hand, Q. variabilis mostly took up water from natural springs (32.3-36.7%) and deep soil layer (33.8-37.1 %) after the rainfall events through its well-developed taproot system. The psi(pd) and psi(md) of Q. variabilis had no significant variation between no rain and light rain events, though they increased significantly for large rainfall and rainstorm events with > 60 cm of soil water recharge provided by the precipitation. The study provides more insights into reforestation and water management in the region of northern China.