Conversion from farmland to orchard reshapes moisture recycling: Mechanistic insights and implications for water management on the Loess Plateau

Moisture recycling is fundamental for regulating water supply in semi-arid regions; however, how vegetation change influences this process remains unclear. This study aimed to clarify how the conversion from farmland to orchard alters land–atmosphere water cycling and provide implications for improving agricultural water management on the Loess Plateau. We combined stable isotope tracing and soil water balance partitioning to quantify moisture recycling rates for different vegetation types (farmland and orchards of varying ages) on the Changwu Loess Tableland in China. We used δ²H–δ¹ ⁸O signatures to partition the contributions of three vapor sources—advection, plant transpiration, and soil evaporation—to precipitation, and further decomposed soil water balance components to interpret the mechanism by which vegetation change influences moisture recycling. After converting farmland to orchards, the soil water stored in 6–20 m declined by 9–20 %, deep percolation decreased from 28 mm·yr⁻¹ to almost zero, and annual soil water deficits reached up to 36 mm; in particular, orchard actual evapotranspiration (ETa) exceeded annual precipitation (105–106 %, compared with 95 % for farmland). The transpiration to actual evapotranspiration ratio (T/ETa) increased from 82 % to 88 %. Consequently, the proportion of recycled moisture in precipitation (fre) increased from 20 % to 25 %, which was driven by a decline in evaporation contribution (fE) and a rise in transpiration contribution (fT), with fT accounting for about 80 % of fre. The proposed Recycling Efficiency Index (REI) revealed that apple orchards are characterized by a high risk of soil water deficit and suboptimal recycling benefits. Collectively, these findings reveal a chain of the vertical water cycle: deep-rooted plants extract deep soil water but limit recharge, and subsequently enhance local moisture recycling by increasing transpiration. Recognizing this dual effect of soil water depletion and enhanced recycling offers insights for improving water use efficiency and guiding sustainable orchard water management on the Loess Plateau.