Objective The dumps of surface coal mines in cold arid regions represent ecologically vulnerable areas formed under extreme disturbance. However, a lack of systematic studies on the vegetation and soils in dumps, including their spatial variation patterns and synergistic mechanisms caused by vertical differences of the dumps, leads to insufficient theoretical bases for formulating differential ecological restoration strategies in engineering practice.

Methods By integrating field ecological surveys and physicochemical tests in the laboratory, this study investigated the dump with elevations ranging from 2498 m-2632 m of the Heishan coal mine on the northern slope of the Tianshan Mountains, Xinjiang. Based on redundancy analysis, the spatial variation characteristics of the plant community structures and soil factors in sample plots at different elevations were comparatively analyzed. In combination with Pearson correlation analysis, the explanatory power of soil factors for plant community diversity was quantified. Finally, the coupling relationships of the plant-soil systems at different elevations, along with their driving mechanisms, were systematically analyzed.

Results and Conclusions  The naturally restored plant communities in the dump are dominated by Agropyron cristatum, Halogeton glomeratus, and Lepidium alashanicum, indicating distinct localization characteristics. The plant community structures exhibit pronounced vertical differentiation, with the number of plant species peaking at 11 at elevations ranging from 2553 m-2576 m. With increasing elevation, species richness and diversity increase significantly, while species evenness shows a downward trend. As elevation increases, soil nutrients (i.e., available phosphorus and rapidly available potassium), the activity of key soil enzymes (i.e., urease, invertase, and alkaline phosphatase), and total microbial count increase initially and then decrease, with maximum values identified at elevations ranging from 2553 m-2576 m. This trend is consistent with the elevation variations of the number of plant communities. The maximum total nitrogen content and dissolved organic carbon content in soils are observed at an elevation of 2632 m. The RDA-derived correlations between plant communities and soil factors indicate that soil factors showing significantly positive correlations with plant species richness and plant community diversity include oxidation-reduction potential, microbial biomass carbon, dissolved organic carbon, total nitrogen, polyphenol oxidase activity, and bacterial count (P< 0.05). These soil factors are also key factors governing plant community structures, affecting the settlement and growth of restored plants. The results of this study can provide a scientifically robust basis for precise ecological restoration of surface coal mines in cold arid regions.