A root–soil association index reveals life‐history strategies of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungal taxa differ in their life-history strategies, including their preferential association with intraradical vs extraradical compartments. We introduce the arbuscular mycorrhizal root-soil association index (AMF-RSI), a novel quantitative index describing the relative association of AM fungi with root vs soil compartments, corresponding to the previously proposed rhizophilic and edaphophilic AM fungi. The AMF-RSI was calculated from metabarcoding data compiled in the GlobalAMFungi database using Hierarchical Modeling of Species Communities and was subsequently applied to assess shifts in AM fungal community traits driven by soil disturbance caused by tillage. We assessed 301 AM fungal taxa and found that AMF-RSI was strongly conserved at the genus level. While the majority of AM fungal taxa from families Archaeosporaceae, Diversisporaceae and Paraglomeraceae exhibited preferential association with soil, taxa within Glomeraceae exhibited high variability in edaphophilic vs rhizophilic strategies. AMF-RSI values predicted AM fungal community responses to soil disturbance, with rhizophilic taxa being more prevalent in tilled soils. The AMF-RSI represents a new quantitative trait distinguishing preferential association of AM fungi with intraradical vs extraradical compartments (edaphophilic vs rhizophilic life-history strategies). Applied at the community level, it provides a tool for characterizing shifts in AM fungal communities in response to environmental conditions.