As a species for ecological restoration in northern China, Tamarix ramosissima plays an important role in river protection, flood control, regional climate regulation, and landscape construction with vegetation. Two sampling sites were selected in the hillside and floodplain habitats along the Lanzhou City, and the xylems of T. ramosissima and potential water sources were collected, respectively. The Bayesian mixture model (MixSIAR) and soil water excess (SW-excess) were applied to analyze the relationship on different water pools and the utilization ratios of T. ramosissima to potential water sources in two habitats. The results showed that the slope and intercept of local meteoric water line (LMWL) in two habitats were smaller compared with the global meteoric water line (GMWL), which indicated the existence of drier climate and strong evaporation in the study area, especially in the hillside habitat. Except for the three months in hillside, the SW-excess of T. ramosissima were negative, which indicated that xylems of T. ramosissima are more depleted in δ²H than the soil water line. In growing seasons, the main water source in hillside habitat was deep soil water (80~150 cm) and the utilization ratio was 63 ± 17% for T. ramosissima, while the main water source in floodplain habitat was shallow soil water (0~30 cm), with a utilization ratio of 42.6 ± 19.2%, and the water sources were different in diverse months. T. ramosissima has a certain adaptation mechanism and water-use strategies in two habitats, and also an altered water uptake pattern in acquiring the more stable water. This study will provide a theoretical basis for plant water management in ecological environment protection in the Loess Plateau.

The stable isotopes (δD and δ¹⁸O) in soil water allow tracing of the flow and transportation of water in the soil. However, there are few studies on the use of soil water stable isotopes to explore the soil water in the floodplain, especially in determining the soil water source and infiltration mechanism. The Bayesian mixing model (MixSIAR) was integrated with the line conditioned excess (lc-excess) of stable isotopes (δD and δ¹⁸O) in precipitation, soil water (0–150 cm), river water, and groundwater to determinate the source and recharge mechanisms of two different soil profile types in the floodplain of the upper Yellow River in Lanzhou, China. The results showed that soil water below 80 cm was affected by river water recharge, affecting soil water content and stable isotopic composition at S1 sampling points (profile parallel to river water); this effect was not observed at S2 (profile is higher than the river water) sampling points. The isotopic compositions of the soil water sources at the two sampling points (S1: δD = −77.41‰, δ¹⁸O = −11.01‰; S2: δD = −74.02‰, δ¹⁸O = −10.56‰) were depleted more than those in the long-term amount-weighted precipitation isotopes (δD = −56.30‰, δ¹⁸O = −8.17‰). The isotope signatures of soil water sources are similar to the isotope characteristics of some high-intensity precipitation events (≥30 mm/day), indicating that soil water originates from a fraction of the total precipitation. The piston flow (60%) and the preferential flow (40%) coexist, but soil moisture and rainfall intensity will affect the sequence of the two infiltration methods. This study provides insights for understanding the hydrological process of the upper Yellow River and evaluating groundwater quality and protecting the floodplain environment.

The stable isotopes (²H, ¹⁸O) of precipitation change due to the sub-cloud secondary evaporation during raindrop fall. The study of the temporal and spatial variation of sub-cloud secondary evaporation and its causes by using hydrogen and oxygen stable isotopes is of great significance to the study of the regional water cycle process. Based on the hourly meteorological data of 648 meteorological stations in 17 provinces (cities) of the Yangtze River Basin from March 2018 to February 2019, we analyzed the temporal and spatial characteristics of precipitation excess deuterium variation (Δd) in the region, based on the improved Stewart model. We discuss the various influence factors under different magnitude Δd value change and the impact factor of each partition sub-cloud secondary evaporation influence of the difference. The results show the following: (1) In terms of hourly variation, the sub-cloud secondary evaporation in the daytime is stronger than that at night. In terms of monthly variation, different regions of the study area have different characteristics; that is, the effect of sub-cloud secondary evaporation is more significant in summer and autumn in the northern subtropics and south temperate zones, and in spring and summer in the mid-subtropics and plateau climate zones. (2) There were significant spatial differences in the study area in different seasons, and the effect of sub-cloud secondary evaporation was the most significant in the plateau climate area throughout the year. (3) When the rainfall is 0–5 mm, the temperature is >30 °C, the vapor pressure is <3 hPa, the relative humidity is 50–60%, and the raindrop diameter is 0.5–1 mm; the sub-cloud secondary evaporation effect is the most obvious.

Caragana korshinskii and Tamarix ramosissima are pioneer shrubs for water and soil conservation and windbreak and sand fixation in arid and semi-arid areas. Understanding the water use patterns of C. korshinskii and T. ramosissima and their response to rainfall is of great importance for their survival in regions where drought occurs. In this work we present the monitoring results of stable isotopes in soil water (depths from 0 to 200 cm), twig xylem water of juvenile, intermediate, and adult C. korshinskii and T. ramosissima . The monitoring campaign took place in western Chinese Loess Plateau from July to October 2020. During the same period, we also measured relevant environmental and meteorological variables and soil water content. The results showed that juvenile and of intermediate age C. korshinskii both mainly absorb water from the surface (0–10 cm) and shallow (10–40 cm) soil layers, but adult C. korshinskii use mainly water from the deep soil layers. Juvenile and of intermediate age T. ramosissima extract water from deep soil layers, while adult T. ramosissima use mainly water from middle (40–100 cm) soil depths. Both plant species increase the proportion of surface and shallow soil layer water after precipitation. This increase is more pronounced and faster for the C. korshinskii of intermediate age rather than for juvenile and adult plants. On the contrary, it is the absorption of surface and shallow soil water from juvenile and of intermediate T. ramosissima plants that fluctuates more after precipitation than from adult plants. Our findings provide a reference for vegetation restoration and ecological management of the western Chinese Loess Plateau.

：In the region of the western Loess Plateau, the practice of mulching has been implemented with the objective of reducing water losses in agricultural contexts. Nevertheless, there is currently a paucity of understanding and quantification of the impact of different mulching conditions on soil water evaporation. The soil water content (SWC) and the isotopic composition of soil and precipitation of Ziziphus jujuba were monitored on a continuous basis under different mulching conditions. The impact of diverse mulching techniques on soil evaporation was investigated through an analysis of their hydrogen and oxygen stable isotope characteristics and secondary index, lc -excess, in conjunction with the Craig-Gordon model. Despite the SWC of each experimental group being similar following a single irrigation event, the isotope values were all more depleted than those observed in the control check (CK). The evaporation loss rate of CK reached its peak on the second day after irrigation, at 16.15%. The evaporation loss of the thickness group demonstrated that T1 was the most effective, followed by T2 and then T3. In the particle size group, the evaporation loss peaked on the sixth day after irrigation, with G1 showing the highest loss at 8.83%, followed by G2 at 9.51% and then G3 at 10.55%. This suggests that the application of mulching sand will result in a reduction in the rate of evaporation. Furthermore, during the growth period of the date palm, the isotope values of T3 and G2 in the 0-30 cm soil layer were relatively depleted in comparison to the other experimental groups. The evaporation loss rates of the thickness groups were highest in May and August, with the highest rates observed in T1 (28.71% and 22.62%) and T2 (28.49% and 22.12%). T3 exhibited the lowest evaporation loss rates in this period, with a peak of 2%. The evaporation loss rate reached a minimum in October (T1: 16.10%; T2: 14.82%; T3: 13.72%), with the lowest value observed for the thickness groups (1.41% and 21.45%). The evaporation loss rate in May was greater than that in August for the particle size group. In particular, the evaporation loss rate of the sand-covered thickness group was significantly lower than that of the sand-covered particle size group. Therefore, adjusting the sand-covered thickness has a more pronounced effect on reducing evaporation and retaining moisture than adjusting the sand-covered particle size, and can more effectively enhance the utilization efficiency of agricultural water. The findings can contribute to a deeper comprehension of the sustainability of orchards in regions with constrained water resources, and provide a scientific foundation for the management of water resources in orchards in arid and semi-arid areas.