Role of host nitrogen use efficiency in determining arbuscular mycorrhizal fungi responses to nitrogen enrichment.

Arbuscular mycorrhizal fungi (AMF) form widespread symbiotic relationships with plants, influencing nutrient acquisition and ecosystem functioning. Although nitrogen (N) enrichment effects on AMF have been widely studied, whether host N-use efficiency (NUE) mediates these responses remains unclear. Here, we integrated a global meta-analysis with a greenhouse experiment using low- and high-NUE maize (Zea mays) cultivars Xianyu335 (XY335) and Qianyu568 (QY568) and a decade-long field experiment using low-NUE Sidan19 (SD19) and high-NUE Jidan27 (JD27). The global synthesis revealed a nonlinear response of AMF to increasing N addition, while the complementary experiments showed that host NUE altered both the response direction and its underlying regulatory pathway. In the field, AMF abundance and richness of SD19 declined linearly with increasing N availability, largely through root morphological plasticity. By contrast, JD27 exhibited a hump-shaped response to N addition, mediated by N-induced soil acidification. Furthermore, N addition altered AMF community composition, inducing taxonomic trade-offs between Glomeraceae and Paraglomeraceae, which contributed to the hump-shaped response of AMF in JD27. Together, our findings identify host NUE as a biological filter that modifies how established plant, soil, and fungal mechanisms regulate mycorrhizal responses to N enrichment, offering critical insights for sustainable agricultural management under future global change scenarios.