Arbuscular mycorrhiza convey significant plant carbon to a diverse hyphosphere microbial food web and mineral-associated organic matter

Summary Arbuscular mycorrhizal fungi (AMF) transport substantial plant carbon (C) that serves as a substrate for other soil organisms, a precursor of soil organic matter (SOM), and a driver of soil microbial dynamics. Using two-chamber microcosms where an air gap isolated AMF from roots, we 13 CO 2 -labeled Avena barbata for six weeks and measured. the C Rhizophagus intraradices transferred to SOM and hyphosphere microorganisms. NanoSIMS imaging, IRMS, 13 C NMR, and SOM density fractionation showed hyphae and roots had similar 13 C enrichment. AMF transferred 0.77 mg C per g of soil (increasing total C by 2%); 33% was found in occluded or mineral-associated pools, primarily as carbohydrates. In the AMF hyphosphere, there was no overall change in community diversity but 36 bacterial ASVs significantly changed in relative abundance. With stable isotope probing (SIP)-enabled shotgun sequencing, we found taxa from the Solibacterales, Sphingobacteriales, Myxococcales and Nitrososphaerales (ammonium oxidizing archaea) were highly enriched in AMF-imported 13 C (>20 atom%). Mapping 13 C-enriched metagenome-assembled genomes to total ASVs showed at least 92 bacteria and archaea were significantly 13 C-enriched. Our results illustrate the quantitative impact of hyphal C transport on the formation of potentially protective SOM pools and indicate microbial roles in the AMF hyphosphere soil food web.