Role of common arbuscular mycorrhizal networks in crop phosphorus uptake and biomass in a maize-soybean intercropping system.

Agricultural crop yields are limited by soil nutrient status and crop nutrient utilization efficiency. Both intercropping and arbuscular mycorrhizal fungal colonization can increase plant nutrient utilization and crop yields. However, although common mycorrhizal networks have been widely studied, the role of arbuscular mycorrhizal fungi in mediating nutrient transfer within networks formed between intercropped plants, and the consequences for the component crops, remain insufficiently resolved. We hypothesized that CMN-mediated P redistribution between intercropped maize (Zea mays L.) and soybean (Glycine max (L.) Merr.) is governed by plant P demand (sink strength), and that the direction and magnitude of P transfer shift under contrasting soil P supply. Here, we combined a five-chamber root device with multi-wavelength quantum-dot P labeling to directly trace CMN-mediated P transfer in a maize–soybean intercropping system. A maize–soybean intercropping system was established in a greenhouse under two phosphorus supply levels (low P, 20 mg kg⁻¹ Olsen-P; high P, 100 mg kg⁻¹ Olsen-P) to investigate P allocation within plant–mycorrhiza associations and mycorrhizal networks. Plant physiological traits (photosynthetic parameters and biomass), root traits, and rhizosphere enzyme activities were simultaneously quantified to link CMN-mediated P transfer with plant performance and soil P cycling. In low-phosphorus conditions, inoculation with Diversispora epigaea significantly improved maize physiological in-dices but had no significant effect on soybean, and facilitated net phosphorus (P) transfer from soybean to maize through the common mycorrhizal network (CMN). Under high-phosphorus conditions, inoculation markedly enhanced soybean physiological indices, inhibited maize growth, and redirected P transfer from maize to soybean via the CMN. Overall, mycorrhizal inoculation increased the total P flux within the maize–soybean intercropping system, and the direction of inter-plant P exchange was regulated by the fungal mycelial network in response to contrasting soil P supply, which altered host P demand.