Grasses and shrubs have decoupled legacy effects related to plant nutrition: the interplay of symbiotic fungi and nutrients in soil

Vegetation patchiness is a distinctive feature of arid ecosystems that strongly shapes plant-soil interactions. While fertility islands are recognized as a critical plant legacy influencing ecosystem functioning, it is not clear whether there is a legacy associated with fungi symbionts in soils. We compared the legacies of arbuscular mycorrhizal fungi (AMF) and dark septate endophyte (DSE) inoculum potential in soil, to determine if they respond to the plant functional type (PFT, grasses and shrubs) and if they overlap spatially with the nutrient legacies. We estimated the soil inoculum potential of AMF and DSE and the soil organic carbon (C), phosphorus (P), and nitrogen (N) concentrations in the soil microsites occupied by the dominant grass and shrub species, and in bare soil microsites distributed in a 6-hectare grazing exclosure in the Patagonian steppe. The AMF inoculum potential was higher in soil microsites conditioned by grasses than in microsites conditioned by shrubs. Instead, the DSE inoculum potential did not differ among microsites and was higher than that of AMF. Furthermore, C and P concentrations were higher in microsites conditioned by shrubs, contrary to AMF inoculum potential. We found that grasses and shrubs have decoupled soil legacies that may alleviate nutrient limitation. While shrubs increase nutrient concentrations, grasses increase AMF inoculum potential. Moreover, the homogeneous distribution of DSE inoculum potential highlights the need to further investigate the role of this group of fungi and its interactions with AMF and soil nutrients in the plant-soil interface.