Temporal dynamics of rhizosphere microbiome assembly and carbon-phosphorus coupling in poplar-medicinal plant intercropping systems

BACKGROUND: Intercropping can reshape the rhizosphere microbiome, but how specific companion plants influence nutrient cycling and host growth remains unclear. We proposed that intercropping poplar with medicinal plants creates distinct rhizosphere niches that select for microbial communities with distinct​ functional potential, thereby improving tree nutrition. RESULTS: Intercropping significantly promoted poplar growth, with increases in diameter at breast height (DBH) of 15.33%, 14.3%, and 15.23% in systems with Anemarrhena asphodeloides, Belamcanda chinensis, and Saposhnikovia divaricata, respectively. Intercropping did not change microbial alpha diversity but led to plant-specific shifts in beta diversity with clear seasonal dynamics. Metagenomic analyses revealed corresponding shifts in the functional potential of microbial communities related to carbon (C) and phosphorus (P) cycling, including genes such as frdC, aldB, ppk2, and phnH. Intercropping, particularly with S. divaricata, was associated with an increased genetic potential for microbial C metabolism and​ a heightened potential for P solubilization. These co-occurring shifts in genetic potential were correlated with greater P accumulation in poplar leaves. Network analysis showed distinct temporal microbial co-occurrence patterns across intercropping treatments, with A. asphodeloides supporting the most interconnected community linked to P mobilization. Three bacterial genera (Priestia, Pseudomonas, Acinetobacter) were strongly associated with key soil nutrient pools. Re-inoculation experiments confirmed their functional roles: Priestia sp. increased N and P retention in the rhizosphere; Pseudomonas sp. promoted plant growth, suggesting a role in​ stimulating plant secondary metabolism; and Acinetobacter sp. enhanced organic C mineralization. CONCLUSIONS: Intercropping with specific medicinal plants structures the rhizosphere microbiome through niche differentiation. This restructuring leads to distinct patterns of microbial functional potential, centered on C and P metabolism, which correlate with improved poplar nutrient acquisition and growth. Our findings, integrating metagenomic inference with experimental validation, provide a framework for selecting companion plants to steer the rhizosphere microbiome toward beneficial functional outcomes in agroforestry systems. Video Abstract.