Drought adaptation strategies of Platycladus orientalis in the Western Loess Plateau: Differential water uptake on sunny and shady slopes

Understanding water use strategies of plants is essential for sustainable water resource management in arid and semi-arid regions. Topography significantly influences water distribution, making it vital to explore vegetation water use strategies across different slopes. Our study aimed to explore the influences of slope orientation on the water use strategies and root system adaptability of Platycladus orientalis in the western Loess Plateau under seasonal climate variability. During the 2024 dry (April−May) and wet (July−August) seasons, we collected xylem and root samples of P . orientalis , soil samples (0−200 cm) and precipitation samples on sunny and shady slopes in the western Loess Plateau. The water uptake strategies and their seasonal dynamics were investigated using stable isotope techniques ( δ 2 H and δ 18 O) coupled with Bayesian mixing model (MixSIAR), with particular emphasis on slope-induced variations in root distribution patterns. In the dry season, P. orientalis on sunny slopes absorbed soil water from the 40−100 cm (29.35%) and 100−200 cm (28.90%) layers, while on shady slopes mainly used water from the 0−10 cm (27.65%), 40−100 cm (26.25%) and 100−200 cm (21.15%). In the wet season, deep soil water remained the main source for sunny slopes (31.95%), whereas shady slopes utilized water evenly from all soil layers. This difference was attributed to the higher percentage of fine root biomass (PFRB) in the 100−200 cm layer on sunny slopes compared to shady slopes. Our findings demonstrated that P. orientalis on sunny slopes adapt to drought environment through developing deeper root systems to access deep soil water, enhancing drought resistance, while those on shady slopes relied more on shallow soil water, requiring supplemental irrigation under extreme droughts. This research supports sustainable vegetation restoration and water resource management in the western Loess Plateau region.