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The stable hydrogen and oxygen isotope technique is typically used to explore plant water uptake; however, the accuracy of the technique has been challenged by hydrogen isotope offsets between plant xylem water and its potential source water. In this study, the soil hydrogen and oxygen isotope waterline was used to correct the hydrogen isotope offsets for Salix psammophila and Caragana korshinskii , two typical shrub species on the Chinese Loess Plateau. Five different types of isotopic data [(i) δ18O, (ii) δ2H, (iii) combination δ18O with δ2H, (iv) corrected δ2H and (v) combination δ18O with corrected δ2H] were separately used to determine the water-use patterns of the two shrubs. The δ2H offset values of S. psammophila and C. korshinskii did not show significant temporal variation among the sampling months (May, July and September) but showed notable differences between the two shrubs (−0.4 ± 0.5‰ in S. psammophila vs −4.3 ± 0.9‰ in C. korshinskii). The obtained water absorption proportion (WAP) of S. psammophila in the different soil layers (0–20, 20–60 and 60–200 cm) did not differ significantly among the five different input data types. However, compared with the input data types (iii) and (v), the data types (i), (ii) and (iv) overestimated the WAP of C. korshinskii in the 0–20 cm soil layer and underestimated that in the 60–200 cm layer. The data type (iii) overestimated the WAP of C. korshinskii in 0–20 cm soil layer (25.9 ± 0.8%) in July in comparison with the WAP calculated based on data type (v) (19.1 ± 1.1%). The combination of δ18O and corrected δ2H, i.e. data type (v), was identified as the best data type to determine the water use patterns of C. korshinskii due to the strong correlation between the calculated WAP and soil water content and soil sand content. In general, S. psammophila mainly used (57.9–62.1%) shallow soil water (0–60 cm), whereas C. korshinskii mainly absorbed (52.7–63.5%) deep soil water (60–200 cm). We confirm that the hydrogen isotope offsets can cause significant errors in determining plant water uptake of C. korshinskii , and provide valuable insights for accurately quantifying plant water uptake in the presence of hydrogen isotope offsets between xylem and source water. This study is significant for facilitating the application of the stable hydrogen and oxygen isotope technique worldwide, and for revealing the response mechanism of shrub key ecohydrological and physiological processes to the drought environment in similar climate regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable isotopes were employed to determine the proportional plant water sources. • Differences in plant water-use pattern existed in pure and mixed plantations. • Severe soil desiccation occurred in mixed plantation due to water competition. • Mixed plantation intensifies soil water competition and groundwater depletion. Multi-species plantation has long been applied in forestry and landscape restoration to provide better ecosystem services and functions. However, the differences in water-use patterns between mixed and pure plantations are poorly understood, especially in the arid/semi-arid artificial desert ecosystems. The stable isotope compositions (δ2H and δ18O) of rainwater, xylem water, soil water, and groundwater were analyzed over three growing seasons (2019–2021) to identify the water-use patterns of Artemisia desterorum Spreng (A. desterorum), Amorpha fruticosea (A. fruticosa) and Pinus sylvestris var. mongolica (P. sylvestris) in pure and mixed plantations in the Mu Us Sandy Land. Seasonally, there was a transference of water-use pattern from deep (moist layer and groundwater) to shallow water sources (active and stable layers) during the transition period between the dry and rainy season for both pure and mixed A. fruticosa and P. sylvestris , which was attributed to dimorphic root systems of arbor and shrub in the water-limited region. However, A. desterorum with shallower roots predominately absorbed water from the active and stable layers across the whole growing season regardless of planting pattern. Annually, the three plant species in pure stands extracted water predominantly from the stable layer (36.97%–46.16%), followed by the active layer (23.55%–36.98%). In the mixed stand, however, all the plants absorbed water mainly from the active layer (33.04%–39.44%), followed by the stable layer (30.46%–33.68%), suggesting that multi-species plantation intensifies shallow soil water competition. Additionally, the proportional contribution of groundwater to plant water uptake under mixed plantation was higher than the pure plantations, causing faster groundwater decline in the mixed stand (0.29 m yr−1) compared to pure stands (0.11–0.20 m yr−1). Our study demonstrates that multi-species plantation in the water-limited desert region intensifies soil water competition and groundwater depletion and thus adversely affects sustainable development goals. [ABSTRACT FROM AUTHOR]

• Water use pattern was investigated for Caragana korshinskii on sunny and shady slopes. • Caragana korshinskii seasonally switched its water sources from different soil layers. • Caragana korshinskii on sunny slope used shallower soil water than that on shady slope. • Root distribution and soil moisture affect water use pattern of Caragana korshinskii. Flexible water use patterns are of great importance for the survival of vegetation in dryland regions. Our study aimed to investigate the influences of season and slope aspect on the water use patterns of Caragana korshinskii on typical shady and sunny slopes on the Loess Plateau in China. We collected xylem water, soil water from the 0–200 cm soil layers, and precipitation in May, July, September and November 2018 and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions. The root distribution of C. korshinskii in the 0–200 cm soil layer on both slopes was also investigated. The 0–20, 20–80, and 80–200 cm soil layers were identified as three potential water sources for C. korshinskii , and their proportional contributions to the plant water supply were calculated using a linear mixed model. The results showed that C. korshinskii on the sunny slope absorbed 89.3% of their water from the 0–20 cm soil layer in May but mainly utilized water from the 0–20 and 20–80 cm soil layers in both July and September, and the total contribution percentages of these layers were 84.5% and 89.2%, respectively. However, C. korshinskii on the shady slope extracted water evenly from all three soil layers in May. Thereafter, the plants absorbed water from the 20–80 and 80–200 cm soil layers in both July and September, and the total contribution percentages of these layers were 96.0% and 91.8%, respectively. In November, C. korshinskii absorbed 84.8% and 78.0% of their water from the 80–200 cm soil layer on the shady and sunny slopes, respectively. The generally shallower soil water use of C. korshinskii on the sunny slope than on the shady slope may be due to the larger fine-root (d < 2 mm) length density in the 0–80 cm soil layer on the sunny slope (1.12 ± 0.28 mm/cm3) than on the shady slope (0.57 ± 0.16 mm/mm3) (P < 0.05). This study indicates that C. korshinskii on both shady and sunny slopes seasonally switched their water sources from different soil water layers during the growing season. However, due to their reliance on soil water at the 0–20 cm depth, which is supplied by unstable rainfall, C. korshinskii on sunny slopes may be more vulnerable to future climatic warming and drying on the Loess Plateau. Our findings provide valuable information related to optimal water management in the afforested shrublands in this region. [ABSTRACT FROM AUTHOR]

Flexible water use patterns are of great importance for planted trees if they are to acclimate to more uncertain future conditions in water-limited regions. This study aims to understand seasonal water use patterns of rainfed jujube trees in stands of various ages. A two-year experiment was conducted at four plantations of different ages (4-, 8-, 15-, and 22-years-old), in which the stable isotope technique was combined with three analytical methods. Soil moisture in the shallow (0–20 cm), middle (20–60 cm), and deep (60–200 cm) layers served as potential water sources for the jujube trees. The results showed that the 4-year-old trees mainly used soil moisture from shallow and middle layers. The 8-year-old trees shifted flexibly their water source between the three layers. However, the 15- and 22-year-old trees often ignored moisture in shallow layers and primarily used water from subsurface layers, obtaining more soil moisture from the middle layer in periods with more rainfall while more soil moisture from the deep layer when the precipitation was low. Compared with the 4- and 8-year-old trees, the two low precipitation periods during the study period clearly resulted in more water use from deep layers for the 15- and 22-year-old trees. Overall, older jujube trees were more dependent on soil water from deeper layers compared to younger trees, resulting in extensive use of soil water from deeper layers which was difficult to be replenished by precipitation. This indicates that older trees are more vulnerable to future prolonged and extremely low precipitation, and measures are needed to improve water status, especially for deeper layers under older trees. [ABSTRACT FROM AUTHOR]

[Display omitted] • Seasonal water use patterns differed among different aged S. psammophila. • 6-yr S. psammophila mainly absorbed 0–120 cm soil water across seasons. • 12- and 18-yr S. psammophila shifted water sources between dry and rainy seasons. • Severe soil desiccation and root die-back occurred in 18-yr S. psammophila stand. • Changes in root distribution and SWC affected age-related water use patterns. Understanding the water use pattern of artificially restored vegetation is important to provide reasonable water management strategies. However, the characteristics, controls and differences of water sources of planted Salix psammophila at different developmental stages remain poorly understood. In this study, the hydrogen and oxygen isotope compositions of xylem water, soil water, and rainwater were measured and coupled with the MixSIAR model to investigate the variations and controls of water use patterns of different aged S. psammophila in a semi-arid region in northeastern Mu Us Sandy Land. Results showed that >60% of water used by 6-yr S. psammophila derived from 0 to 120 cm soil layer throughout the growing season due to the relatively shallow roots (0–100 cm). In contrast, water sources used by 12- and 18-yr S. psammophila differed markedly between the dry and rainy seasons, which were attributed to the developed dimorphic root systems and seasonal changes in soil water profile. In the dry season, 12- and 18-yr S. psammophila extracted 71.93% and 68.91% of water from 120 to 300 cm and 40–200 cm soil layer, respectively; in the rainy season, however, they both shifted main water sources to 0–120 cm soil layer (65.09% and 56.14%). The severe soil desiccation and dead roots observed in the 18-yr stand decreased the ability of old S. psammophila to extract water from the deep soil layer (200–300 cm) in the dry season. Thus, changes in the vertical distribution of roots and soil water contents controlled the seasonal water use pattern of different aged S. psammophila. Our study demonstrates that the age-dependent water use pattern of S. psammophila should be considered to implement the corresponding management measures in future afforestation plans to avoid overuse of water and maintain sustainable vegetation restoration in the water-limited desert regions. [ABSTRACT FROM AUTHOR]