Community Structure of Arbuscular Mycorrhizal Fungi in Soils of Switchgrass Harvested for Bioenergy

Learning more about the biodiversity and composition of arbuscular mycorrhizal fungi (AMF) under alternative agricultural management scenarios may be important to the sustainable intensification of switchgrass grown as a bioenergy crop. Using PacBio single-molecule sequencing and taxonomic resolution to the level of amplicon sequence variant (ASV), we assessed the effects of nitrogen amendment on AMF associating with switchgrass and explored relationships between AMF and switchgrass yield across three sites of various productivities in Wisconsin. Nitrogen amendment had little effect on AMF diversity metrics or community composition. While AMF ASV diversity was not correlated with switchgrass yield, AMF family richness and switchgrass yield had a strong, positive relationship at one of our three sites. Each of our sites was dominated by unique ASVs of the species Paraglomus brasilianum, indicating regional segregation of AMF at the intraspecific level. Our molecular biodiversity survey identified putative core members of the switchgrass microbiome, as well as novel clades of AMF, especially in the order Paraglomerales and the genus Nanoglomus. Furthermore, our phylogenies unite the cosmopolitan, soil-inhabiting clade deemed GS24 with Pervetustaceae, an enigmatic family prevalent in stressful environments. Future studies should isolate and characterize the novel genetic diversity found in switchgrass agroecosystems and explore the potential yield benefits of AMF richness. IMPORTANCE We assessed the different species of beneficial fungi living in agricultural fields of switchgrass, a large grass grown for biofuels, using high-resolution DNA sequencing. Contrary to our expectations, the fungi were not greatly affected by fertilization. However, we found a positive relationship between plant productivity and the number of families of beneficial fungi at one site. Furthermore, we sequenced many species that could not be identified with existing reference databases. One group of fungi was highlighted in an earlier study for being widely distributed but of unknown taxonomy. We discovered that this group belonged to a family called Pervetustaceae, which may benefit switchgrass in stressful environments. To produce higher-yielding switchgrass in a more sustainable manner, it could help to study these undescribed fungi and the ways in which they may contribute to greater switchgrass yield in the absence of fertilization.