Unraveling the role of hyphal networks from arbuscular mycorrhizal fungi in aggregate stabilization of semiarid soils with different textures and carbonate contents

Our study was intended to elucidate the involvement of three species of arbuscular mycorrhizal fungi (AMF) in the formation and stabilization of aggregates in semiarid soils with different textures and calcium carbonate contents. We used a root-hyphae compartment approach to compare the effect of three AMF (Rhizophagus irregularis, Septoglomus deserticola, and Gigaspora gigantea) on the structural stability of the hyphosphere (root-free hyphae) and mycorrhizosphere (hyphae + root) soil of Olea europaea plants grown in two soils differing in their texture (sandy loam and silty loam) and calcium carbonate content. Only the R. irregularis strain significantly increased the percentage of stable aggregates in both types of soil, being the increases higher in the hyphosphere compartment (on average, about 30 % compared to non-inoculated soil). In the hyphosphere compartment of both soils, the hyphal length developed by plants inoculated with R. irregularis was 81 % greater than that of non-inoculated plants. The effect of the AMF on soil aggregation was mediated by mechanical entanglement of mycorrhizal fungal hyphae but without a contribution of labile carbohydrates. The ability of extraradical hyphae to improve soil structure was independent of the soil texture and content of carbonates.