Seasonal water sources and response to precipitation events of Calligonum mongolicum at the oasis margin in the Hexi River Corridor

Abstract

Calligonum mongolicum is often planted as a windbreak and for sand stabilization on mobile and semi‐mobile sand dunes in extremely arid regions. However, water availability remains a key limiting factor for its survival and population expansion, and water use strategies and responses to precipitation events of this species are unknown. Here, we determined water use strategy of C. mongolicum under extreme arid conditions by measuring the oxygen stable isotopes (δD and δ18O) in xylem water and in potential water sources (precipitation, soil water, and groundwater). We used the IsoSource model to determine the relative contributions of different water sources to water utilization by C. mongolicum. Our results showed that: (1) water sources used by C. mongolicum exhibited seasonal variability, with shallow soil water accounting for 42% of utilization during early spring (April), and deep soil water and groundwater being predominantly used during the summer and autumn and accounting for 61%–84% of utilization, (2) C. mongolicum did not respond to small precipitation events, but responded significantly to large precipitation events. C. mongolicum maintained the utilization of soil water in all layers at 74%–81% of deep soil water and groundwater before a 5.8 mm precipitation event. A precipitation event of 18.8 mm increased the contribution of surface water from 4% before to 17% after precipitation, indicating that C. mongolicum has a strong capacity for self‐regulation and adaptation; namely, C. mongolicum is capable of developing an optimal phenotype through self‐regulation, thereby maximizing water acquisition.