Abstract: Aims Arbuscular mycorrhizal fungi (AMF) can enhance the competitive ability of invasvie plant against native species, which is likely influenced by soil nitrogen forms. Against the backdrop of increasing nitrogen deposition, exploring the effects of AMF on the growth and competitiveness of invasive plants under different forms of nitrogen addition can enhance our understanding of how invader adapts to soil nitrogen patterns shaped by nitrogen deposition. Methods A common garden experiment was conducted using the invasive plant Bidens alba and the native species Emilia sonchifolia. The experimental design included two planting regimes (monoculture and mixture), three nitrogen treatments (ammonium [NH₄⁺], nitrate [NO₃⁻], and no nitrogen addition), and two microbial treatments (with or without AMF). Important findings Under all nitrogen treatments, AMF significantly increased the biomass of the native plant E. sonchifolia. Specifically, when grown in monoculture with NO3- addition, AMF exhibited the greatest promotiing effect on its biomass, indicating high mycorrhizal dependence in the native species, which is also influenced by soil nitrogen forms. AMF did not show a significant impact on the invasive plant B. alba under either monoculture or mixed planting. The greatest enhancement of the competitive response of B. alba by AMF occurred under no nitrogen addition, but no evidence was found that AMF could help the invasive plant adapt to different forms of nitrogen to maintain its competitiveness. This may be related to its strong mycorrhizal autoregulation. ability. The results suggest that the invasive plant B. alba thrive under high nitrogen deposition conditions through direct nutrient uptake pathways and its mycorrhizal autoregulation ability. This study demonstrates that plant-AMF symbiosis is influenced by nitrogen addition and nitrogen forms, highlighting the importance of nitrogen forms in shaping the mycorrhizal responses of invasive plants and deepening the understanding the role of AMF in growth and competitive response of invasive plants under nitrogen deposition.

Key words: AMF, Nitrogen deposition, Nitrogen forms, Plant invasion, Competitive response