Abstract: Exploring the responses of urban trees to large and continuous nitrogen deposition is one of the foundations for solving the functional issues of urban green space ecosystems.To investigate the response mechanism of Robinia pseudoacacia 'Hongsen' to continuous nitrogen (N) deposition and the specificity of its biomass allocation strategy, a 6-month controlled experiment simulating short-term N deposition was conducted with NH₄NO₃ as the N source. Four treatments were established: CK (control, 0 g·m⁻²·a⁻¹), LN (low N, 5g·m⁻²·a⁻¹), MN (medium N, 10 g·m⁻²·a⁻¹), and HN (high N, 15 g·m⁻²·a⁻¹). The results revealed the following: (1) N deposition significantly increased plant height, ground diameter, specific leaf area (SLA), as well as the biomass of stems, leaves, roots, and total biomass,while significantly reducing specific root length (SRL); (2) SRL,SLA,and plant height exhibited a "low-promotion and high-inhibition" response to N deposition. Biomass in the LN and HN treatments was primarily allocated to aboveground parts, whereas in the MN treatment, biomass tended to be allocated to the root system; (3) N deposition elevated the N content in stems, leaves, and roots of Robinia pseudoacacia 'Hongsen' seedlings.Plant height(H),ground diameter(D),specific leaf area(SLA), stem biomass(SB), leaf biomass(LB), root biomass(RB), root weight ratio (RMR), root-shoot ratio (R/D), and RB were all positively correlated with N content,while SRL and SMR were negatively correlated with plant N content.These findings indicate that Robinia pseudoacacia 'Hongsen' employs distinct biomass allocation strategies to adapt to N deposition, and a certain level of N deposition can promote the productivity of Robinia pseudoacacia 'Hongsen'.