Native plant invasion mediates coupled homogenization of soil metabolomes and microbial functional groups on the Qinghai-Tibetan Plateau

Abstract Alpine grasslands on the Qinghai-Tibetan Plateau (QTP) are experiencing severe degradation, increasingly driven by the invasion of native poisonous plants. However, current research has primarily focused on aboveground ecological processes, leaving our understanding of the dynamics and driving mechanisms of belowground biodiversity and functioning during this invasion still limited. In this study, we combined field surveys (15 paired soil samples) with a controlled pot experiment (n = 32) to assess how the common native invasive plant Ligularia cymbulifera alters the diversity, composition, and assembly mechanisms of soil microbial functional groups (e.g., taxa involved in C/N cycling, mycorrhizal symbionts, and pathogens) on the QTP. Our findings demonstrated that native invasive plants restructure divergent microbial functional groups at both alpha and beta diversity levels, and this restructuring was associated with changes in allelochemical profiles. These shifts revealed two distinct ecological consequences. (1) Soil acidification and nutrient enrichment promoted specialized functional groups, thereby elevating alpha diversity. (2) Concomitant chemical homogenization reduced the spatial heterogeneity of microbial functional groups, suppressed beta diversity, and induced biotic homogenization. Crucially, plant–soil feedback experiments indicated that these homogenized microbes suppressed forage seedling growth. We document that increased local (α) diversity can coincide with reduced spatial (β) diversity, a potential paradox for ecosystem resilience. Sustainable solutions require integrating microbial regulation into alpine restoration frameworks to mitigate instability from microbial homogenization alongside establishing a “plant-soil-microorganism interplay” paradigm to counteract diversity and function cascades initiated by native invasive plants.