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Feedbacks between plants and surrounding soil microbes can contribute to the establishment and persistence of invasive annual grasses as well as limit the success of restoration efforts. In this study, we aim to understand how three sources of soil inocula – native, invasive (from under Bromus diandrus) and sterile – affect the growth response and fungal community composition in the roots of a chaparral shrub, Adenostoma fasciculatum. We grew A. fasciculatum from seed in a greenhouse with each inoculum source and harvested at six months. We measured above- and below-ground biomass, arbuscular mycorrhizal fungal (AMF) colonization and conducted targeted-amplicon sequencing of the 18S and ITS2 loci to characterize AMF and general fungal community composition, respectively. Native inoculum resulted in roots with richer communities of some groups of AMF and non-AMF symbionts, when compared to roots grown with invasive or sterile inoculum. Seedlings grown with invasive and native inoculum did not have different growth responses, but both produced more biomass than a sterile control. These findings suggest that inoculation with soil from native species can increase the diversity of multiple groups of fungal symbionts and inoculation with live soil (invasive or native) can increase seedling biomass. Moreover, future work would benefit from assessing if a more diverse community of fungal symbionts increases seedling survival when planted in field restoration sites.

Fungal community composition in the Anthropocene is driven by rapid changes in environmental conditions caused by human activities. This study examines the relative importance of two global change drivers – atmospheric nitrogen (N) deposition and annual grass invasion – on structuring fungal communities in a California chaparral ecosystem, with emphasis on arbuscular mycorrhizal fungi. We used molecular markers, functional groupings, generalized linear statistics and joint distribution modeling, to examine how environmental variables structure taxonomic and functional composition of fungal communities. Invasive grasses had a lower richness and relative abundance of symbiotic fungi (both AMF and other fungi) compared to native shrubs. We found a higher richness and abundance of rhizophilic (e.g. Glomeraceae) and edaphophilic (e.g. Gigasporaceae) AMF with increasing soil NO 3. Our findings suggest that invasive persistence may decrease the presence of multiple soil symbionts that native species depend on for pathogen protection and increased access to soil resources. [ABSTRACT FROM AUTHOR]

• Live soil inoculation caused seedlings to produce more biomass. • Roots grown with native inoculation had higher AMF and non-AMF colonization. • Native inoculation promotes more diverse communities of AM and EM fungi. Feedbacks between plants and surrounding soil microbes can contribute to the establishment and persistence of invasive annual grasses as well as limit the success of restoration efforts. In this study, we aim to understand how three sources of soil inocula – native, invasive (from under Bromus diandrus) and sterile – affect the growth response and fungal community composition in the roots of a chaparral shrub, Adenostoma fasciculatum. We grew A. fasciculatum from seed in a greenhouse with each inoculum source and harvested at six months. We measured above- and below-ground biomass, arbuscular mycorrhizal fungal (AMF) colonization and conducted targeted-amplicon sequencing of the 18S and ITS2 loci to characterize AMF and general fungal community composition, respectively. Native inoculum resulted in roots with richer communities of some groups of AMF and non-AMF symbionts, when compared to roots grown with invasive or sterile inoculum. Seedlings grown with invasive and native inoculum did not have different growth responses, but both produced more biomass than a sterile control. These findings suggest that inoculation with soil from native species can increase the diversity of multiple groups of fungal symbionts and inoculation with live soil (invasive or native) can increase seedling biomass. Moreover, future work would benefit from assessing if a more diverse community of fungal symbionts increases seedling survival when planted in field restoration sites. [ABSTRACT FROM AUTHOR]