Mikania micrantha invasion restructures rhizosphere nitrogen cycling through enzyme activation, microbial recruitment, and allelopathic regulation

BACKGROUND: Plant invasions profoundly influence terrestrial ecosystems by reshaping nutrient cycling processes. However, the mechanisms through which invasive plants such as Mikania micrantha modulate soil nitrogen (N) cycling and microbial communities remain insufficiently explored. Moreover, comparative studies with indigenous congener are scarce, limiting insights into whether such effects reflect species-specific strategies or genus-wide traits. This study investigates how M. micrantha modulates nitrogen metabolic pathways and rhizosphere microecology using combined metagenomic and metabolomic analyses. RESULTS: Integrated analyses revealed that M. micrantha established a distinctive "high total nitrogen-low mineral nitrogen" profile in the rhizosphere soil. Metagenomic profiling showed consistent enrichment of key ammonium assimilation enzymes, including glutamine synthetase and glutamate dehydrogenase, promoting enhanced incorporation of NH₄⁺ into organic nitrogen pools. In contrast, genes encoding nitrate reductase and nitrate transporters were significantly lower in relative abundance, limiting nitrate assimilation. Mikania micrantha also selectively enriched nitrogen-fixing microbes (notably rhizobia genera) and plant growth-promoting rhizobacteria (PGPR), thereby enhancing biological nitrogen fixation capacity. Metabolomic analysis further identified several allelopathic compounds in invaded soils at higher relative abundance, particularly epicatechin, which exhibited inhibitory effects on nitrifying bacteria. Compared with the congener Mikania cordata, which exerted weaker impacts on soil nitrogen cycling and microbial assembly, M. micrantha deployed a more comprehensive strategy integrating biochemical, microbial, and metabolic regulation. CONCLUSIONS: These findings demonstrate that under greenhouse-controlled conditions, M. micrantha reconfigures rhizosphere nitrogen cycling through a multi-dimensional strategy that couples biochemical regulation, microbial recruitment, and metabolite-mediated interference, thereby suggesting a potential mechanism that may contribute to its ecological advantage in natural settings. Video Abstract.