Water use characteristics of coexisting sand‐binding vegetation in two typical soil habitats in the desert steppe of China

Abstract Understanding the water use characteristics and water relationship of coexisting vegetation in a mixed‐species plantation of trees and shrubs is crucial for the sustainable restoration of degraded arid areas. This study investigated the water use characteristic of coexisting sand‐binding vegetation combinations in the sierozem habitat ( Populus przewalskii Maxim namely Populus‐S and Caragana liouana ) and aeolian sandy soil habitats ( Populus przewalskii Maxim namely Populus‐A and Salix psammophila ) of the desert steppe. By analysing the δ 2 H and δ 18 O isotopes in xylem, soil water, groundwater and precipitation, a Bayesian MixSIAR model was employed to quantitatively assess the water utilization characteristics of plants. Throughout the growing season, in the sierozem habitat, C. liouana exhibits the highest efficiency in utilizing soil moisture above 60 cm (53.45%) and displays adaptable water use strategies. In contrast, Populus‐A predominantly relies on deep soil moisture below 60 cm plus groundwater (63.89%). In the aeolian sandy soil habitat, both Populus‐A and S. psammophila similarly favour deep soil moisture below the 60 cm soil plus groundwater (66.77% and 67.60%, respectively). During the transition period from the dry to the wet seasons, although both Populus‐A and S. psammophila in the aeolian sandy soil habitat shifted their water sources from deeper to shallower ones, there was considerable overlap in the water sources used by Populus‐A and S. psammophila . This overlap led to competition for water resources and exacerbated the depletion of deep soil moisture in both seasons. Conversely, in the sierozem habitat, the partitioning of water sources between Populus‐S and C. liouana facilitated the allocation and utilization of water resources between the two species. The findings highlight the need for species‐specific consideration in water resource allocation within mixed‐species plantations of trees and shrubs, which is crucial for sustainable vegetation restoration in sand‐binding ecosystems.