Spatiotemporal differentiation and trade-off/synergy relationships of ecosystem service values in Mountain-Oasis-Desert System of Xinjiang Aksu region.

Understanding how land use/cover change (LUCC) mediates the interactions among ecosystem services (ES) is crucial for sustaining fragile landscapes worldwide. This study addresses this challenge in the arid Mountain-Oasis-Desert System (MODS), a coupled socio-ecological complex where water-limited environments intensify human-nature conflicts. Taking the Aksu MODS as a typical case, we developed an integrated assessment framework combining a locally calibrated Ecosystem Service Value (ESV) model with the biophysical InVEST model (for carbon storage, habitat quality, and water yield) to analyze ES dynamics and their trade-offs/synergies from 1990 to 2020. Results revealed a dramatic LUCC, with cultivated and construction land expanding by 83.06% and 93.19%, respectively, at the expense of grassland and water areas. Consequently, total ESV declined markedly, exhibiting increasing spatial heterogeneity. A fundamental subsystem divergence emerged: while synergistic relationships dominated in mountain and desert areas, the human-dominated oasis became a hotspot of trade-offs, with 81.82% of ES pairs showing significant trade-offs, particularly between food production and water-related regulation. InVEST modeling corroborated this pattern, indicating stable total carbon storage (~ 4.0 × 10⁹ t) but a severe decline in water yield (from 1.82 × 10⁶ mm to 0.86 × 10⁶ mm), with grassland degradation serving as a key proximate mechanism. Our findings demonstrate that ES interactions are not uniform but are fundamentally shaped by subsystem-specific LUCC trajectories. This underscores the imperative of spatially differentiated management to mitigate trade-offs in vulnerable arid landscapes.