Soil erosion is a primary driver of Mollisol degradation and threatens the stability of soil conservation services in agroecosystems. However, how erosion resistance reorganizes under increasing degradation constraints, and how biological regulation becomes limited, remains poorly understood. Here, straw incorporation, grass and legume cover crops (winter wheat, ryegrass, hairy vetch, and a ryegrass-vetch mixture), and their combinations were evaluated under simulated slight, moderate, and severe degradation, using maize monoculture as a control. Erosion resistance was assessed from two complementary dimensions-aggregate stability and resistance to hydraulic detachment-while dominant regulatory pathways were identified using random forest analysis and partial least squares path modeling. All management practices enhanced erosion resistance relative to the control, but their effectiveness and underlying mechanisms varied systematically with degradation intensity. Under slight to moderate degradation, grass cover crops exerted stronger control over detachment resistance than straw, whereas straw-cover crop integration showed complementary effects on overall erosion resistance. As degradation intensified, these complementary effects weakened, and under severe degradation, legume cover crops surpassed grasses and straw in improving erodibility resistance. Across all degradation levels, root traits dominated erosion resistance, shifting from indirect, soil-property-mediated pathways under slight degradation to direct mechanical reinforcement under moderate to severe degradation. Concurrently, these soil properties along with soil organic carbon and its fractions, increasingly constrained erosion resistance, setting upper limits to biological regulation. These results demonstrate that erosion resistance in Mollisols does not respond linearly to management practices but undergoes degradation-dependent functional reorganization. From an agroecosystem management perspective, these findings indicate that the effectiveness of conservation practices is strongly conditioned by degradation status, rather than being universally transferable across Mollisol systems. By identifying constraint-driven shifts in root-soil-carbon regulation, this study clarifies when biological management can effectively sustain soil conservation services in agroecosystems and when its effectiveness becomes inherently limited.