Abstract Moso bamboo ( Phyllostachys edulis ) expansion threatens subtropical forest biodiversity, yet how intraspecific root trait variation shapes rhizosphere microbial functional potential remains unclear. We aimed to elucidate how bamboo root trait variation and rhizosphere soil properties jointly shape microbial functional gene profiles during expansion. We investigated paired pure bamboo forests (PBF) and mixed bamboo forests (MBF) at four elevations in subtropical China, integrating individual‐level root trait measurements, rhizosphere soil analyses and shotgun metagenomic profiling. Bamboo in MBF exhibited acquisitive root strategies with significantly higher specific root length (615.33 vs. 446.03 cm/g) and specific root area (156.06 vs. 122.86 cm 2 /g), but lower root tissue density (0.32 vs. 0.39 g/cm 3 ) compared to PBF. PBF rhizospheres harboured significantly enriched nitrogen and phosphorus cycling genes, with co‐occurrence networks showing substantially higher connectivity in phosphorus metabolism (1520 vs. 788 edges). Structural equation modelling demonstrated that forest type shaped functional gene assembly primarily through soil property modification, with root traits exerting limited direct effects. These findings reveal that established bamboo stands develop self‐reinforcing microbial feedbacks through soil modification, creating functionally integrated rhizosphere communities with enhanced nutrient cycling potential. Expansion fronts, where these feedbacks are not yet established, offer a critical window for management intervention before positive feedbacks strengthen. Read the free Plain Language Summary for this article on the Journal blog.
Wu et al. (Fri,) studied this question.