Characteristics and sources of soil moisture dynamics in alpine meadows under simulated warming conditions

This study quantified the dynamics and sources of soil moisture in alpine meadows under experimental warming during 2023–2024 at the observation and research Station of eco-hydrology and national park by stable isotope tracing in Qilian Mountains. Except for the shallow layer (0–10 cm) under warming plus increased precipitation (ZWZY), overall soil water content in 2024 exceeded that in 2023; in 2023, all depths in the warming treatment (ZWCK) were drier than the control (CKCK). Soil-water isotopes showed evaporative enrichment from June (δ18O ≈ −9.88 ‰; δ2H ≈ −77.41 ‰) to the peak-heat period in July (≈ −6.70 ‰; ≈ −40.46 ‰), followed by monsoon-driven depletion and isotopic convergence in August. The summer soil–water line slope (≈ 6.64) was lower than the local meteoric water line (≈ 7.71), indicating non-equilibrium evaporation, whereas rapid post-storm isotope shifts between July and October point to precipitation-pulse-dominated recharge. Among environmental controls, soil temperature was the primary driver of isotopic variability, with precipitation as a secondary control. Mechanistically, piston flow contributed ≥ 85 % in June–July and October, while heavy rainfall increased preferential flow to 38–48 % in August–September. We propose a warming-responsive restoration framework for alpine meadows: canopy retention to damp heat load, three-tier water management (surface–root zone–subsoil), and targeted night-time water supplementation to buffer future climate uncertainty.