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.

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.