Abstract
Water is the most important factor limiting the growth of sand-binding vegetation (SBV) in desert ecosystems. This study explored the water sources and water use strategies of SBV under a natural precipitation gradient. Six typical SBV species were selected, comprising three tree species, Pinus sylvestris, Haloxylon ammodendron and Populus euphratica, and three shrub species, Artemesia ordosica, Caragana korshinshii and Tmarix ramosissima. The stable isotope values (δD, δ18O) of xylem water and potential water sources (precipitation, soil water, and groundwater) of these species under a precipitation gradient in the sandy regions of northern China were measured. In addition, the relative contributions of the different potential water sources to water use by SBV were analyzed using the MixSIAR model. The results indicated that the Local Meteoric Water Lines (LMWLs) of the six SBV species were located on the right side of the Global Meteoric Water Line (GMWL), with the degree of deviation gradually increasing with a decrease in precipitation. The results showed that T. ramosissima, H. ammodendron and P. euphratica mainly used groundwater (GW), whereas P. sylvestris, A. ordosica and C. korshinshii mainly used soil water. Among those species using soil water, P. sylvestris and A. ordosica mainly used shallow soil water (20–80 cm). P. sylvestris and C. korshinshii showed the highest soil water utilization rate of 14%, whereas P. euphratica showed the lowest soil water utilization rate of 2%. The different SBV species showed significantly different soil water utilization rates due to the influence of plant root distribution (p < 0.001). Among the six SBV species, trees showed a higher GW utilization rate compared to shrubs at 65.74% and 47.29%, respectively, whereas shrubs showed a higher deep soil water utilization rate (140–200 cm) compared to trees at 65.74% and 47.29%, respectively. The precipitation utilization rates amongst the six SBV species were highest in spring, followed by autumn and summer. The utilization of GW by SBV will be intensified in the future due to climate change. However, the stability of T. ramosissima may pose a threat due to its low utilization rate of GW.
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