Trait-based assembly of arbuscular mycorrhizal fungal communities determines soil carbon formation and retention.

Fungi are crucial for soil organic carbon (SOC) formation, especially for the more persistent mineral-associated organic C (MAOC) pool. Yet, evidence for this often overlooks arbuscular mycorrhizal fungi (AMF) communities and how their composition and traits impact SOC accumulation. We grew sudangrass with AMF communities representing different traits conserved at the family level: competitors, from the Gigasporaceae family; ruderals, from the Glomeraceae family; or both families combined. We labeled sudangrass with C-CO to assess AMF contributions to SOC, impacts on SOC priming, and fungal biomass persistence in MAOC. Single-family AMF communities decreased total SOC by 13.8%, likely due to fungal priming. Despite net SOC losses, all AMF communities contributed fungal C to soil but only the Glomeraceae community initially contributed to MAOC. After a month of decomposition, both the Glomeraceae and mixed-family communities contributed to MAOC formation. Plant phosphorus uptake, but not hyphal chemistry, was positively related to AMF soil C and MAOC accumulation. Arbuscular mycorrhizal fungi contribution to MAOC is dependent on the specific traits of the AMF community and related to phosphorus uptake. These findings provide insight into how variations in AMF community composition and traits, and thus processes like environmental filtering of AMF, may impact SOC accumulation.