Introducing native species to enhance multifunctionality of reclaimed soil and its mechanism in dumps of open-pit coal mines on Loess Plateau

The single vegetation zonal planting restoration model commonly used in open-pit coal mine dump sites on the Loess Plateau restricts the associations and feedbacks among vegetation diversity, microbial community complexity, and soil multifunctionality, leading to generally poor long-term effects of single-vegetation restoration. To address this, Ulmus species were introduced into the pure Pinus tabuliformis forest reclamation area of the South Dump Site in Antaibao Open-Pit Coal Mine, Shuozhou, Shanxi Province. Surface soil samples (0–20 cm) were collected under three restoration modes: pure P. tabuliformis (YS), Ulmus + P. tabuliformis mixed forest (MS), and pure Ulmus control (CK). Soil physical-chemical properties, microbial community diversity, and other indicators were measured to explore the mechanism of native species introduction on soil microbial communities, soil multifunctionality, and their variations. The results showed: Native species introduction significantly improved soil microbial diversity (p < 0.01) and multifunctionality (p < 0.001), with most indices of soil α-diversity and multifunctionality under the MS treatment outperforming other treatments. Microbial network complexity and stability increased significantly after introducing native Ulmus (p < 0.01). The MS mode exhibited the highest topological properties, including total node number, total link number, link density, average degree, and average clustering coefficient, while showing the lowest vulnerability and average path length. The complexity of soil bacterial networks, microbial multidiversity, and physicochemical parameters such as NH₄⁺-N and AP are key factors influencing soil multifunctionality (p < 0.05), with their importance values being 27.19%, 18.72%, 37.15%, and 22.94%, respectively. Native species introduction exerted direct positive effects and indirectly influenced microbial diversity, network complexity, and soil multifunctionality by regulating soil physical-chemical properties and extracellular enzyme activities. Network complexity explains soil multifunctionality more strongly than microbial diversity. Introducing native tree species to form coniferous-broadleaved mixed forest structures enriched litter and root exudate types, significantly improving environmental factors, microbial communities, and multifunctionality of reclaimed soil in open-pit coal mines on the Loess Plateau. The mechanism of vegetation diversity in improving reclaimed soil microbial communities and multifunctionality was revealed, providing the reference for understanding the interactions between biodiversity and soil multifunctionality and scientifically formulating vegetation restoration strategies for open-pit coal mining areas on the Loess Plateau, China.