Root traits and soil phosphorus gradients determine crop-specific responsiveness to arbuscular mycorrhizal fungi

BACKGROUND AND AIMS: Despite growing recognition of phosphorus (P) acquisition via arbuscular mycorrhizal fungi (AMF), the drivers of crop-specific variation in mycorrhizal responsiveness remain unresolved. METHODS: We quantified growth and P acquisition responses to AMF across six maize, eight cotton, and nine wheat varieties under three soil Olsen-P levels (4, 18, and ≥60 mg kg-1). KEY RESULTS: AMF effects were strongly crop-dependent. Cotton exhibited consistent mutualistic responses, with increased biomass and P uptake, whereas wheat frequently showed neutral or negative growth responses, and maize responses were largely neutral. Mycorrhizal responsiveness was jointly shaped by soil P availability and root traits, peaking at intermediate Olsen-P levels. Species with finer roots exhibited stronger dependence on AMF, whereas those with coarser roots showed weaker responses. Rhizosphere pH positively modulated responsiveness under low-P conditions, while acid phosphatase activity was driven solely by soil P availability. CONCLUSIONS: These findings identify soil P gradients as a primary regulator of mycorrhizal responsiveness across crops, while highlighting root diameter and rhizosphere pH as key trait-based and environmental modulators.