Lack of complementary or synergistic benefits of arbuscular mycorrhizal fungi (AMF) and organic amendments but functional differentiation among AMF species in a maize–wheat rotation

: Organic amendments (OAs) and arbuscular mycorrhizal fungi (AMF) are promising tools for improving soil fertility and crop productivity in nutrient-poor soils. While AMF, biochar, and compost have shown complementary or synergistic effects under controlled conditions, their field-scale interactions remain poorly understood. In a two-year maize-wheat rotation, we applied OAs (biochar or compost) and AMF inocula (three isolates each of Funneliformis mosseae, FmMix, and Archaeospora trappei, ArMix) alone or combined with OAs. We tested whether AM inoculation enhances maize productivity and soil fertility, shows complementarities or synergisms with compost and/or biochar, whether effects persist in wheat, and if plant and soil responses differ by AM fungal species. Maize yield increased with AMF and OA, but the combined application did not yield a significant increase over the effect of each factor operating independently. A similar pattern was found for grain nutrients and soil (bio)chemical parameters, except for a complementary effect of FmMix with compost+biochar on maize P uptake. AMF applied with compost and biochar synergistically promoted fungal biomass, and the effect persisted in wheat with ArMix. Although yield did not differ between AM species, interspecies functional variability was observed in grain nutrients and soil enzymes. FmMix enhanced maize P and wheat K, Mg, and Fe, while ArMix increased maize Cu and Ca, and wheat P, Zn, and Cu. Our findings emphasize that the effectiveness of AMF and OAs is influenced by OA properties, soil conditions, crop and AM species. Although functional interspecies variability was observed, the comparable or superior agronomic benefits of A. trappei indicates that lesser-known AM taxa hold promise as efficient inoculants.