Phosphorus-dependent shifts in acquisition strategies revealed by integrated transcriptomics and metabolomics in soybean roots

Under phosphorus (P) deficiency, soybean (Glycine max L.) adapts by modifying root architecture, increasing the release of organic exudates, and engaging arbuscular mycorrhizal (AM) symbiosis. However, how these strategies trade off across a P gradient remains unclear. In this study, we integrated transcriptomic and metabolomic analyses to examine five soybean cultivars under soil P supplies of 0 mg P kg⁻¹ (severe deficiency, P0), 30 mg P kg⁻¹ (moderate deficiency, P30), 60 mg P kg⁻¹ (mild deficiency, P60), 90 mg P kg⁻¹ (adequate, P90), and 120 mg P kg⁻¹ (excess, P120). Our results indicate that plant-available P is associated with shifts among three P acquisition strategies in soybean. In contrast to P90, the P30 treatment exhibited a 56–321% increase in AMF colonization and elevated expression of PPDK, accC, and FabI. The P0 treatment, meanwhile, was characterized by a 17–24-fold increase in organic acid exudation, a 35% increase in SRL, and upregulation of the genes pckA, MDH, aceB, and CS. Cultivars differed in their adaptive preferences: AM-dependent types were better suited to moderate P limitation, whereas fine-rooted cultivars were advantageous under severe P depletion. Overall, our findings reveal the regulatory networks underlying soybean P-acquisition strategies and highlight their breeding and management significance. This study provides a foundation for developing P-efficient soybean cultivars and for precision P management in sustainable agriculture.