Aims <p>Soil cadmium (Cd) contamination and associated carbon loss are critical environmental issues. Switchgrass (<i>Panicum virgatum</i> L.) cultivation offers a solution by integrating phytoremediation with carbon sequestration.</p> Methods <p>We conducted a one-year pot experiment to evaluate two switchgrass ecotypes (upland and lowland) under nitrogen (N) regimes (0, 60&#xa0;kg N ha⁻¹) across five soil Cd concentrations (0, 1, 10, 20, and 30&#xa0;mg&#xa0;kg⁻¹). Biomass allocation, N uptake efficiency, Cd phytoextraction, greenhouse gas (GHG) emissions, and net ecosystem carbon balance (NECB) were systematically quantified.</p> Results <p>Under high Cd stress (30&#xa0;mg&#xa0;kg⁻¹), the upland ecotype showed stronger carbon sequestration stability with a more stable NECB by reducing 19% root/shoot ratio (RSR), whereas the lowland exhibited a significant decline, increasing its RSR by 26%. N application strongly promoted Cd phytoextraction, increasing it by 165% in the upland ecotype, though N₂O emissions also rose by 22–57%. The upland also demonstrated superior carbon sequestration stability, with only a 6% increase in CO₂ emissions under high Cd, versus 25% for the lowland.</p> Conclusions <p>Our findings underscore the superior capacity of the upland ecotype for simultaneous Cd phytoremediation and carbon stabilization, suggesting that ecotype-specific N management can optimize environmental outcomes.</p> Graphical Abstract <p></p>