Apple orchards are widely distributed perennial agroecosystems with high water demand, in which evapotranspiration (ET) and its partitioning are critical to orchard water use, plant productivity and regional hydrological processes. Although previous studies have examined transpiration (T) and ET in apple orchards at local or site scales, a global synthesis of the variability and controlling factors of T, ET and transpiration-to-evapotranspiration ratio (T/ET) is still lacking. Here, we synthesized data from 83 peer-reviewed articles covering 88 sites, 87.5% of which were in drylands. Using a Boosted Regression Trees (BRT) model, we identified twelve biotic and abiotic factors regulating ET partitioning in apple orchards. Across all sites under their respective climatic and orchard management conditions, the mean actual crop transpiration (Tc act), actual crop evapotranspiration (ETc act) and actual crop transpiration-to-evapotranspiration ratio (Tc act/ETc act) were 2.09 ± 1.14 mm d⁻¹ , 2.51 ± 1.10 mm d⁻¹ and 0.57 ± 0.15, respectively. The BRT results showed that abiotic factors explained most of the variability in Tc act and ETc act, whereas biotic factors contributed more to the variation in Tc act/ETc act. Management practices also significantly affected ET partitioning. Among them, irrigation significantly increased Tc act/ETc act (0.64 ± 0.10, p < 0.05), whereas mulching and pruning had limited effects. This study provides the first global quantitative synthesis of ET partitioning in apple orchards and offers a scientific basis for improving orchard water management and water-use efficiency worldwide.
