Stable oxygen-hydrogen isotopes reveal water use strategies of Tamarix taklamakanensis in the Taklimakan Desert, China

Abstract

Tamarix taklamakanensis, a dominant species in the Taklimakan Desert of China, plays a crucial role in stabilizing sand dunes and maintaining regional ecosystem stability. This study aimed to determine the water use strategies of T. taklamakanensis in the Taklimakan Desert under a falling groundwater depth. Four typical T. taklamakanensis nabkha habitats (sandy desert of Tazhong site, saline desert-alluvial plain of Qiemo site, desert-oasis ecotone of Qira site and desert-oasis ecotone of Aral site) were selected with different climate, soil, groundwater and plant cover conditions. Stable isotope values of hydrogen and oxygen were measured for plant xylem water, soil water (soil depths within 0-500 cm), snowmelt water and groundwater in the different habitats. Four potential water sources for T. taklamakanensis, defined as shallow, middle and deep soil water, as well as groundwater, were investigated using a Bayesian isotope mixing model. It was found that groundwater in the Taklimakan Desert was not completely recharged by precipitation, but through the river runoff from snowmelt water in the nearby mountain ranges. The surface soil water content was quickly depleted by strong evaporation, groundwater depth was relatively shallow and the height of T. taklamakanensis nabkha was relatively low, thus T. taklamakanensis primarily utilized the middle (23%±1%) and deep (31%±5%) soil water and groundwater (36%±2%) within the sandy desert habitat. T. taklamakanensis mainly used the deep soil water (55%±4%) and a small amount of groundwater (25%±2%) within the saline desert-alluvial plain habitat, where the soil water content was relatively high and the groundwater depth was shallow. In contrast, within the desert-oasis ecotone in the Qira and Aral sites, T. taklamakanensis primarily utilized the deep soil water (35%±1% and 38%±2%, respectively) and may also use groundwater because the height of T. taklamakanensis nabkha was relatively high in these habitats and the soil water content was relatively low, which is associated with the reduced groundwater depth due to excessive water resource exploitation and utilization by surrounding cities. Consequently, T. taklamakanensis showed distinct water use strategies among the different habitats and primarily depended on the relatively stable water sources (deep soil water and groundwater), reflecting its adaptations to the different habitats in the arid desert environment. These findings improve our understanding on determining the water sources and water use strategies of T. taklamakanensis in the Taklimakan Desert.

The Stem Sap Flow and Water Sources for Tamarix ramosissima in an Artificial Shelterbelt With a Deep Groundwater Table in Northwest China

“…To maintain transpiration when the moisture content of the shallow and middle soil layers is extremely low, T. ramosissima needs to take-up water from deep soil layers and groundwater. Although the δ 18 O values for T. ramosissima xylem water have a slight seasonality, deep soil water and groundwater are the main water sources, which are a finding that are consistent with previous studies (Chen et al, 2017;Li et al, 2019;Dong et al, 2020). In generally, water sources for plants are affected by soil water conditions and by plant root systems (Asbjornsen et al, 2007;Dong et al, 2020).…”

“…Thus, the stable isotope characteristics of terrestrial ecosystem can provide distinct trace information for water exchange between soil, plant, and atmosphere in the terrestrial ecosystem (Pan Y.-X. et al, 2020), which has been extensively utilized to quantify plant water sources (Li et al, 2019;Dong et al, 2020;Pan Y.-X. et al, 2020).…”

The Ecological Relationship of Groundwater–Soil–Vegetation in the Oasis–Desert Transition Zone of the Shiyang River Basin

“…Desert vegetation communities in the Shiyang River Basin are usually composed of shrubs and herbs (Figure 5). The roots of shrubs and herbs in arid areas are mainly distributed at a depth of 1.2 m below the soil surface (Figure 12a) [47][48][49][50]. The water in this layer is the main water source that supports the growth of vegetation, which indicates the ecological significance of soil moisture in the surface unsaturated zone.…”

“…This type of vegetation has become an important part of the vegetation in this area [46,52]. The trees and some shrubs with a root depth of 4-10 m mainly rely on deep groundwater to survive [49,53]. When the GWD is less than 4 m, the roots of the vegetation can grow vertically and penetrate the groundwater surface or reach the groundwater capillary water uplift zone (Figure 12c).…”

“…Hence, the vegetation no longer completely depends on the surface soil moisture to survive. When the GWD is further reduced to 2 m, vegetation growth can fully access soil moisture and groundwater to survive [54] (e.g., some species of Tamarix [49,55]), and thus VFC can reach a higher value [56]. Figure 11b displays the relationship between GWD and VFC when GWD <4 m. These two were highly negatively correlated (R = −0.78).…”