Spatio-temporal coupling of mulching duration and irrigation regulates soil hydro-thermal dynamics and root niche differentiation in an alley cropping system

Context: Optimizing soil hydro-thermal dynamics is critical for sustaining agroforestry productivity in semi-arid regions, yet the coupling effects of plastic mulching and irrigation on root niche differentiation remain poorly understood under inter-annual climatic variability.,Objective: This study investigated the trade-offs between resource-driven production potential and resilience-driven stability in an apple-soybean alley cropping system on the Loess Plateau, aiming to optimize the spatio-temporal coupling of water and heat.,Methods: Using a three-year field experiment (2021–2023) on the Loess Plateau, soil hydrothermal dynamics, root niche differentiation, and system productivity were quantified across orthogonal combinations of three irrigation limits (50%, 65%, 80% of field capacity; W1–W3) and two mulching durations (half-period mulching vs. full-period mulching; M1–M2). High-frequency in-situ monitoring and structural equation modeling (SEM) were employed to decipher the coupling mechanisms driving system resilience.,Results: Results revealed a distinct "phase-dependent functional duality" of mulching. Temporally, continuous mulching (M2) evolved from an early-stage insulator into a maladaptive "thermal trap" during the reproductive stages of the dry year (2022), exacerbating heat stress and intercepting critical summer rainfall. In contrast, dynamic removal (M1) restored the soil-atmosphere continuum, enhancing summer infiltration and cooling. Spatially, moderate irrigation (W2) maintained an optimal vertical moisture gradient. This physicochemical regulation drove significant root plasticity: the optimized W2M1 configuration induced a spatial niche differentiation (shallow soybean foraging vs. deep apple rooting), significantly reducing the Pianka overlap index from 0.88 to 0.77. Consequently, W2M1 achieved the highest system stability and Water Use Efficiency (WUE) (increased by 30.4% on average, and up to 54.7% in the dry year compared to continuous mulching), despite a slight yield trade-off compared to high-input regimes (W3M2). Structural Equation Modeling (SEM) confirmed that optimized root distribution was the pivotal driver of this resilience.,Significance: These findings challenge the static "resource supplementation" paradigm. We propose a climate-smart strategy—combining moderate irrigation with dynamic mulch removal—to reconcile the trade-off between yield maximization and ecological stability in water-limited agroforestry.