Extreme precipitation rapidly recharges desiccated deep soil and restores deep root water uptake in a rainfed apple orchard: Implications for water management in deep-rooted agroecosystems

Deep soil water is a critical resource for deep-rooted tree crops in water-limited regions, yet progressive desiccation of deep layers under rainfed plantations may erode the long-term drought resilience of these systems and threaten their productivity. However, the extent to which extreme rainfall events can recharge desiccated deep soil and restore deep root water uptake remains poorly quantified. To address this gap, we used the 2021 extreme wet year, when annual precipitation reached 920 mm—approximately 1.6 times the long-term mean—as a natural experiment in a mature rainfed apple orchard on the Loess Plateau of China. We compared soil water dynamics down to 20 m, tree transpiration, and stable-isotope-based water source partitioning in 2017 and 2023, representing conditions before and after the extreme wet year, to quantify how extreme precipitation altered deep soil water reserves and plant water use. Extreme precipitation rapidly replenished the 3–10 m soil layer, increasing water storage by about 350 mm. The infiltration rate reached 5 m yr⁻1—approximately 25 times faster than previously reported piston flow rates, indicating preferential-flow-dominated deep recharge. This replenishment reduced transpiration stress: despite a lower leaf area index in 2023 than in 2017, actual transpiration increased from 213 to 232 mm, and the Ta/Tp ratio rose from 0.57 ± 0.24 to 0.78 ± 0.31. In addition, the contribution of soil water from 3–10 m depth to transpiration increased from 50 ± 12% in 2017 to 62 ± 12% in 2023, indicating a shift in water uptake from shallow to deeper soil layers. These findings demonstrate that episodic extreme precipitation can reverse deep soil desiccation in deep-rooted rainfed orchards, and provide a quantitative basis for rainwater-harvesting and infiltration-enhancing strategies that convert such events into a hydraulic buffer against drought in water-limited agricultural regions under a changing climate.