Arbuscular mycorrhizal fungi originated from soils with a fertility gradient highlight a strong intraspecies functional variability

Characterization and selection of arbuscular mycorrhizal fungal (AMF) taxa to design inocula tailored to meet a spectrum of needs is a crucial first step to achieve specific beneficial agronomic functions. Commonly, commercial microbial inocula are based on generalist single AM fungal taxa, having low genetic variability and not offering efficiency and stability when applied in agroecosystems. In this study, we investigated the AMF functional variability at inter- and intra-species levels by characterizing colonization traits, host growth, and mineral uptake of single-spore AM fungi isolated from soils with a fertility gradient. Nineteen single-spore cultures, showing high spore density and AMF colonization, were phylogenetically assigned to different isolates of 3 AMF species (i.e. Entrophospora claroidea, Funneliformis mosseae and Archaeospora trappei). A higher functional variability in infectivity and effectiveness was detected among isolates within AMF species (25 % of total variance) than among AMF species. Most of AMF isolates of F. mosseae have a better outcome in terms of plant growth, although with a performance gradient, while the isolates of E. claroidea showed a variable functional pattern, and those of A. trappei a less variable pattern. Overall, isolates originating from the soil of the conventional arable field with higher pH and phosphorous availability promoted the uptake of plant nutrients, while those originating from soils with higher SOM and plant diversity promoted plant growth. On the contrary, the infectivity traits of the AM fungi were more conserved, as they were not affected by the environmental parameters of the soils of origin. Finally, we highlighted that soil pH played an important role in shaping the pattern of AMF functionality. Boosting the isolation and cultivation of AMF taxa, originating from agricultural and natural soils, is shown to be a key step in exploiting AMF diversity and designing the new generation of microbial inoculants.