Aims The relationships between nitrogen (N) and phosphorus (P) acquisition strategies among herbaceous legume species remain poorly understood, particularly in relation to how they are altered by N availability. This study aimed to investigate the relationships between N-2 fixation, plant N concentration and P acquisition through two main strategies in temperate herbaceous legumes, and to demonstrate the influences of soil N availability on these relationships. Methods In a field pot experiment, eight temperate herbaceous legumes were grown with or without N addition. Plant growth, plant N and P concentrations, N-2 fixation, arbuscular mycorrhizal (AM) fungal colonization and root phosphatase activity (RPA) were measured, and the relationships between N-2 fixation, plant N concentration and each P acquisition strategy were assessed under contrasting N availability. Results N addition increased RPA. However, AM fungal colonization showed species-specific responses to N addition, and the ratio of AM fungal colonization to root phosphatase activity was decreased by N addition. Among eight legume species, AM fungal colonization increased with N-2 fixation rate in the absence of N addition, but no relationship was observed with N addition. RPA increased with plant N concentration among legume species, regardless of N addition. Conclusions As two key P acquisition strategies, neither RPA nor AM fungal colonization of temperate herbaceous legumes were species-specific traits, since both were positively correlated with N-2 fixation rate and plant N concentration. In addition, the correlation between N-2 fixation and AM fungal colonization was regulated by N availability. While N enrichment intensifies the legume reliance on RPA for acquiring more P, it weakens the association of N-2 fixation in driving across species AM colonization.