Native plant effects on soil multifunctionality are mediated by microbial network reorganization in a subalpine spoil dump

Engineering activities have led to a worldwide increase in spoil dumps, posing severe challenges to ecological restoration, particularly in vulnerable ecological regions. Identifying suitable restoration strategies is critical for the rapidly re-establishment soil multifunctionality to prevent secondary degradation and geohazards. In this study, we established a revegetation field experiment at a spoil dump on the eastern Tibetan Plateau, using four plant species with divergent functional traits, including Artemisia dubia, Melilotus suaveolens, Piptanthus nepalensis, and Rumex nepalensis. After two growing seasons, rhizosphere soils of the targeted species were collected and compared with bulk soils as controls. Soil multifunctionality was used as an integrated index to evaluate the restoration effectiveness. Our results showed that the rhizosphere of A. dubia (dense fine roots) supported significantly higher bacterial Shannon diversity and Pielou evenness than other treatments. Microbial co-occurrence networks were generally simplified in the rhizosphere compared to bulk soils. Soil functions related to C and N cycling, and overall soil multifunctionality were significantly enhanced in the rhizosphere across all species compared to bulk soils, but inter-species differences in these functions were limited. R. nepalensis (well-developed taproot) exerted the strongest positive effect on soil multifunctionality. Structural equation modeling revealed that plant traits shaped soil multifunctionality primarily through indirect pathways by alleviating nutrient imbalances and altering microbial attributes. Our findings highlight that the rapid improvement of soil multifunctionality is driven by the reorganization of microbial co-occurrence networks mediated by plant functional traits, rather than by microbial diversity. This work provides novel insights into plant-soil-microbe interactions in engineered-disturbed ecosystems, and underscores that trait-based configuration of native species represents a promising strategy for restoring the belowground functions of vulnerable alpine spoil dumps.