To clarify the influence of plant roots on the frost heave characteristics of sandy soil under subzero temperatures, unidirectional freezing tests were conducted using sandy soil and the typical desert vegetation Alhagi sparsifolia from the Manas River Basin in Xinjiang. The effects of root content on soil temperature, moisture content, and frost heave displacement during subzero freezing were examined, and the underlying mechanisms were explored. It was found that Alhagi sparsifolia roots mitigates the initial temperature drop during the early cooling stage, thereby improving the frost resistance of the soil. Seepage conditions are enhanced by the presence of roots, facilitating moisture migration and reducing soil moisture content. The relative change magnitude in the average moisture content of the root-soil composite is 1.42 to 2.27 times greater than that of bare soil. Mechanically, roots exerts an anchoring effect that restricted soil particle displacement. These thermal, hydraulic, and mechanical effects collectively contributes to the inhibition of frost heave deformation. An optimal range of root content is identified for maximizing frost heave reduction under various temperatures and initial moisture contents. Specifically, at initial moisture contents of 12% and 14%, a root content of 0.49% resulted in a maximum frost heave reduction of 70.03% compared with bare soil. At initial moisture contents of 8% and 10%, an optimal root content range of 0.28% to 0.42% yields a maximum reduction of 76.92%.The research findings can provide theoretical support for the design of frost heave prevention in hydraulic projects in seasonal frozen soil regions and for desert ecological slope protection projects, offering a new approach for using native vegetation in ecological restoration in frozen soil areas.