Arbuscular Mycorrhizal Fungi-Mediated Reconfiguration of Poplar Leaf C-N-P Metabolic Networks: Environment-Dependent Synergies and Nutrient Interactions

The regulatory mechanisms by which AMF modulate the integrated carbon (C)-nitrogen (N)-phosphorus (P) metabolic network in woody plant leaves remain unclear. We investigated how varying nitrate (NO₃^-) and phosphate (Pi) supply, with or without AMF inoculation, reshapes the leaf metabolic network in poplar seedlings. Key findings reveal that AMF acts as a central metabolic hub, optimizing C-N-P coordination in an environment-dependent manner. Under low Pi, NO₃^- supply enhanced P remobilization and photosynthetic efficiency, boosting growth. AMF further optimized low-Pi adaptation by promoting P storage and buffering, significantly improving photosynthesis and biomass. Under high Pi, NO₃^- supply shifted focus towards enhancing Rubisco-mediated carbon assimilation. AMF synergistically improved carbon assimilation efficiency and suppressed non-essential P recycling. N metabolism effects of Pi were contingent on NO₃^- availability, and AMF reprogrammed N assimilation pathways accordingly, balancing uptake and utilization under different N regimes. Critically, AMF orchestrated environment-specific metabolic adjustments, reinforcing P buffering and photosynthetic gain under Pi limitation, and enhancing C assimilation efficiency while minimizing P waste under Pi sufficiency. This study demonstrates that poplar leaf C-N-P networks are reconfigured through N-P synergisms modulated by AMF, positioning AMF as a pivotal integrator of nutrient acquisition and allocation. These insights provide a physiological foundation for developing efficient forestry nutrient management and mycorrhizal application strategies.