Water use characteristics of native and exotic shrub species in the semi-arid Loess Plateau using an isotope technique.
Knowledge of the processes underlying plant water use characteristics is critical for understanding soil-plant interactions and evaluating plant adaptability in water-limited ecosystems. The vegetation on the Loess Plateau has - dramatically changed due to the implementation of the Grain-for-Green Project from 1999. Despite this, water use characteristics of native and exotic shrub species remain poorly understood in this region. In this study, seasonal variations of water use characteristics of Spiraea pubescens (a native shrub) and Hippophae rhamnoides (an exotic shrub) in the Loess Plateau were investigated by examining the δ2H and δ18O of xylem and soil water from different soil layers within 300 cm of the surface, as well as the δ13C in plant leaves. Results revealed that H. rhamnoides and S. pubescens derived ∼80% of their water sources from the 0-120 cm soil layer during the growing seasons. However, H. rhamnoides absorbed higher proportions of deep soil water (120-300 cm) as the growing season progressed. H. rhamnoides flexibly converted its water source between shallow (0-40 cm) and deep soil layers. Moreover, H. rhamnoides had higher leaf-level water use efficiency than that of S. pubescens. These results suggest that H. rhamnoides has a greater degree of ecological plasticity in water use. Flexible water use characteristics are relevant to functionally dimorphic root systems as an adaptation strategy for the plants in water-limited environments. These findings indicate that water use characteristics of these plants should be considered when exotic species are introduced for revegetation in semiarid regions.