Spatiotemporal optimization of micro-spray misting for orchard microclimate regulation and water-use efficiency in semi-arid apple orchards.

Global warming has intensified heat and drought stress in semi-arid orchard systems, posing major challenges to sustainable apple production. Although micro-spray misting can simultaneously regulate canopy cooling and humidification, orchard responses to different spatiotemporal misting configurations remain insufficiently understood. In this two-year field study, we evaluated the effects of three misting heights (upper, middle, and lower canopy) and four misting durations (0.5-2.0 h) on orchard microclimate, physiological activity, fruit production, and water-use performance in semi-arid apple (Malus domestica Borkh.) orchards. Moderate misting applied within the middle canopy for 1.5 h (H2T2) most effectively improved the orchard microenvironment, reducing average canopy temperature by 4.3 °C and increasing relative humidity by 5.7%. This treatment enhanced photosynthetic performance and water-use efficiency at both leaf and orchard scales and resulted in the highest fruit yield and best overall fruit quality. Comprehensive multi-criteria evaluation further placed the 1.0 h middle-canopy treatment (H2T3) in the same top-performance tier as H2T2. Moving beyond discrete treatment-level comparisons, response surface analysis identified a continuous range of near-optimal parameter combinations within the tested parameter space. Specifically, a duration of 0.70-1.46 h and a misting height of 74-113 cm maintained ≥95% of the maximum predicted response, revealing a stable and feasible operational range rather than a single optimum under field conditions. These findings demonstrate that orchard responses to micro-spray misting are governed by both misting height and operating duration, and that moderate middle-canopy misting with intermediate operating duration provides a practical management strategy for optimizing canopy microenvironments and water-use efficiency under heat and drought stress in semi-arid apple production systems.