Plant Species Shape the Arbuscular Mycorrhizal Community and Plant Performance in Legume Crops and Weeds

Arbuscular mycorrhizal (AM) fungi are often considered host generalists. Although the host-mediated assembly of AM fungal communities is well documented, its functional significance remains poorly understood, particularly in organic and low-input agroecosystems, where crop–weed interactions may influence the soil AM fungal reservoir. We investigated plant and AM fungal functional traits, mycorrhizal dependency (MD), and root AM communities in three legume crops and five weed species grown in pots with the same indigenous AM fungal inoculum. AM fungal communities were characterized using SSU rRNA gene clone libraries, sequencing, and terminal restriction fragment length polymorphism (T-RFLP) analysis. Of 825 examined clones, 792 were assigned to AM fungi, representing 23 RFLP types. Plant species significantly affected the plant traits, root colonization, spore density, extraradical mycelium density, and MD. PERMANOVA revealed that plant species explained 97.3% of the variation in the AM fungal community structure, although this result should be interpreted cautiously because within-species dispersion may have contributed to the explained variance. RELATE analysis showed a significant association between the AM fungal community structure and plant–AM fungal functional traits. The specific root length, shoot and root N concentrations, AM fungal colonization, and spore abundance best explained community patterns. Legume crops supported greater AM fungal development and positive growth responses, whereas several weeds hosted diverse AM communities without showing biomass benefits. These findings highlight that weed management could indirectly influence AM fungal persistence through host-mediated community assembly, although field validation is required.