LAUSR

Invasive plants often exhibit a competitive advantage over native species, posing a serious threat to them. Phytohormone signalling can regulate the entire process of invasive plant growth and defence in ways that have largely unexplored for invaders in competitive conditions. Here, we planted an invasive species, Flaveria bidentis L., and three native species (Setaria viridis, Artemisia annua, and Xanthium sibiricum) as monocultures (two seedlings each) or mixtures (one F. bidentis with one native) in the greenhouse, then employed phytohormone metabolomics and transcriptomics to investigate the changes in hormone content and their gene expression patterns in F. bidentis during competitive processes with native plants. Our results revealed that during competition processes with three native species, the levels of growth‐promoting hormones, auxin (indole‐3‐acetic acid) and gibberellins (GA3), significantly increased in F. bidentis. These hormone increases were accompanied by the key up‐regulation of genes in the auxin and gibberellin signalling pathways (e.g., ARF and GID1), which effectively spurred increases in plant height and biomass. Conversely, the levels of defence‐related hormones, jasmonic acid and salicylic acid were significantly reduced, along with the down‐regulation of genes in their signalling pathways, including COI1 and TGA. These decreases in defence‐related hormones and gene expression alleviated the antagonistic effects on growth‐promoting hormones, enabling F. bidentis to grow more rapidly and enhance its competitive advantage. Synthesis and applications. Our findings reveal that trade‐offs between growth and defence hormone signalling pathways enhance the competitive advantage of invasive alien species over native ones. This insight into the invasive success of exotic species provides a foundation for developing targeted control strategies. By specifically regulating hormone signalling pathways, the competitiveness of invasive species could be dampened, thereby mitigating the threat to native ecosystems.