Abstract: Flaveria bidentis (L.) Kuntze, a common invasive plant in North China, significantly changes soil nutrient properties upon entering new habitats, posing a threat to native species and biodiversity. However, there is still a gap in the understanding of competitive dynamics between F. bidentis and native species after invasion. To further investigate this invasion mechanism, a series of monoculture and mixed plant replacement experiments were conducted with F. bidentis and native competitors within invaded communities. The native species included Setaria viridis (L.) Beauv, Artemisia annua L., and Xanthium sibiricum Patrin ex Widder. Their growth indices (such as plant height, biomass, and relative growth rate) and physiological markers (including photosynthesis and enzyme activities) were measured to understand the physiological and ecological differences between plants under different competition scenarios. The results showed that compared with monoculture settings, the growth indicators such as plant height, biomass, and relative growth rate of F. bidentis in mixed planting treatment were significantly improved (P<0.05). In contrast, native species exhibited the opposite trend, with A. annua showing the greatest decrease in growth index under mixed cropping conditions compared to monoculture environments. In addition, compared with monoculture conditions, the photosynthetic indices of F. bidentis under mixed planting conditions, including net photosynthetic rate, stomatal conductance, inter-cellular CO₂ concentration and transpiration rate, were significantly higher (P<0.05). Furthermore, the activities of glutamine synthetase and glutamate synthetase, which are related to ammonium nitrogen metabolism in F. bidentis, were significantly increased (P<0.05) in comparison to monoculture settings. Conversely, the activities of nitrate reductase and nitrite reductase, integral to nitrate nitrogen metabolism in native species, were notably lower (P<0.05) under mixed planting conditions. These findings underscore the superior competitive prowess of F. bidentis relative to native species. F. bidentis showed heightened vigor in ammonium nitrogen metabolism during competition, suppressing the growth and development of native species while fostering its own rapid proliferation. This study elucidates the invasion mechanism of interspecific competition among native species and provides a theoretical framework for mitigating the invasion and proliferation of F. bidentis.