Abstract:The Fenhe River Basin is a critical ecological zone in the middle reaches of the Yellow River, which has been featured by both fragile ecosystem and intensive human activities. It is of great significance to clarify the trade-off mechanism of ecosystem services (ESs) to support the ecological protection and sustainable development. This study innovatively categorized the types of ESs trade-off based on comparative advantages, and investigated the spatio-temporal patterns and nonlinear drivers of trade-offs among carbon sequestration (CAS), water yield (WAY), and soil conservation (SOC) from 2000 to 2020 through Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model as well as Random Forest model and Shapley Additive Explanations (SHAP). The results showed that: (1) CAS and SOC showed a continuous increasing trend from 2000 to 2020, while WAY decreased slightly before a significant increase in 2020. Type 1 CAS-WAY trade-offs exhibited a steady rise across most regions except the plain area, where they suddenly decreased in 2020. Type 2 CAS-WAY trade-offs in mountain area remained relatively stable over two decades, though temporal trends varied among the plain, platform, and hilly areas. The temporal trend of the type 1 CAS-SOC trade-offs differed across geomorphological zones, while the type 2 CAS-SOC trade-offs were stable but experienced a sharp increase in 2020. (2) From 2000 to 2015, the spatial extent of type 1 CAS-WAY trade-offs gradually expanded, whereas type 2 trade-offs underwent a relative contraction, this trend then reversed in 2020. The spatial distribution of both type 1 and type 2 CAS-SOC trade-offs were stable from 2000 to 2015 but shifted into a spatial pattern where type 2 trade-offs dominated in 2020. (3) Factors such as land use, precipitation, slope gradient, temperature exhibited threshold effects on both type 1 and type 2 trade-offs, which were the results of the comprehensive interactions among multiple factors. The interaction effects between forest cover and precipitation, construction land and precipitation, cropland and slope gradient showed distinct trends. For example, at a lower forest cover proportion, even with lower precipitation, the trade-off of type 1 CAS-WAY can still be mitigated. As the forest cover proportion increased, the interaction effect exhibited two distinct patterns: below 700 mm of precipitation, the trade-off was enhanced, while above 700 mm of precipitation, the trade-off was declined. The interaction effects offered critical insights for guiding land use allocation strategies under diverse climatic and topographic conditions. This study enriches the understanding of the "black box" trade-off mechanism, and is expected to comprehensively support the practice of ecological protection and restoration.