Mycorrhizal Networks Enhance Nitrogen Uptake in Pinus massoniana Lamb. Seedlings via Rhizosphere Microbiome and Root Exudate Modulation

[Aims] Mycorrhizal networks (MNs) critically enhance plant nitrogen (N) acquisition, yet their mechanisms in Pinus massoniana remain elusive. [Mthods] Therefore, ectomycorrhizal fungi Sm（a mixture of three fungi: Pisolithus orientalis (Po), Scleroderma citrinum (Sc), and Suillus luteus (Sl)）were used to establish mycorrhizal networks between donor (Sm-G) and recipient (Sm-S) P. massoniana seedlings. [Results] Using a ¹⁵ N tracer and metagenomics, we showed that the mycorrhizal networks inoculation increased biomass (13.9-fold) and N uptake (18.5-fold). Specifically, Sm-G secrete flavonoids to recruit Proteobacteria for ammonium retention, while Sm-S release coumarins to enrich Actinobacteria for nitrate reduction. These shifts suppressed nitrification (↓M00528) while enhancing assimilation (↑K02575) and nitrate reduction (↑K00360), redirecting N toward plant-available forms. [Conclusion] Our findings unveil a tripartite mechanism where the mycorrhizal networks mediate root exudate-microbe interactions to drive N cycle efficiency, offering novel insights into belowground plant-microbe crosstalk and informing sustainable afforestation practices.