Divergent water use strategies of three desert shrubs on the Alxa plateau: insights from stable isotopes and root distribution analysis

Introduction Understanding how desert shrubs partition water sources is critical for predicting ecosystem responses to increasing drought and guiding restoration efforts in arid regions. However, the water use strategies of coexisting shrubs in cold deserts remain poorly resolved, particularly under varying soil moisture conditions. Methods We quantified the water uptake patterns of three dominant desert shrubs ( Caragana korshinskii, Ammopiptanthus mongolicus , and Reaumuria soongarica ) on the Alxa Plateau, China, using stable hydrogen (δD) and oxygen (δ 18 O) isotopes in precipitation, soil water, xylem water, and groundwater, combined with leaf δ 13 C analysis and root distribution measurements. The Bayesian mixing model (MixSIAR) was used to estimate the proportional contributions of six soil layers to plant water uptake under wet, moderate, and dry soil moisture conditions. Results The three species exhibited distinct water use strategies. C. korshinskii consistently obtained 70-90% of its water from the 40-100 cm soil layer across all moisture conditions, showing the lowest water absorption plasticity (CV=15.5%). A. mongolicus shifted flexibly between the 20-60 cm and 60-80 cm layers (CV=16.5%), while R. soongarica displayed a bimodal strategy, switching from the 0-20 cm layer under wet conditions to the 60-100 cm layer under drought (CV=16.3%). Leaf δ 13 C values confirmed a depth-water use efficiency (WUE) trade-off, with deeper-rooted species exhibiting higher intrinsic WUE. Discussion These findings reveal species-specific water partitioning strategies that reflect differences in root architecture and hydraulic regulation. The results provide a mechanistic basis for targeted ecological restoration: C. korshinskii is suited for dune crests with deep stable moisture, A. mongolicus for intermediate slopes benefiting from dimorphic roots and nitrogen fixation, and R. soongarica for microsites that episodically concentrate surface water. Such species-site matching can enhance restoration success under projected drier climates.