The mandate by the Energy Independence and Security Act of 2007 to increase renewable fuel production in the United States has resulted in extensive research into the sustainability of perennial bioenergy crops such as switchgrass (Panicum virgatum) and miscanthus (Miscanthus × giganteus). Grasslands planted with these species can support greater biodiversity and ecosystem function than annual crops. However, management considerations, such as which species to plant and whether to use nitrogen fertilizers, may alter belowground diversity and ecosystem functioning associated with these grasslands. In this study, we compared differences in arbuscular mycorrhizal fungal (AMF) and soil nematode abundance, activity, and diversity associated with switchgrass and miscanthus under fertilized and non-fertilized conditions in a long-term experiment established as part of the Great Lakes Bioenergy Center at the W.K. Kellogg Biological Station in Michigan, USA. We quantified crop AMF root colonization, AMF extra-radical hyphal length, soil glomalin concentrations, AMF richness and diversity, plant-parasitic nematode abundance, and nematode family richness and diversity in each treatment.
Plots planted to switchgrass had higher levels of mycorrhizal activity and diversity than miscanthus, and this coincided with higher potential soil carbon contributions via hyphal growth and glomalin production. Plant parasitic nematode (PPN) abundance was 1.5x higher in miscanthus plots compared to switchgrass, mostly due to increases in dagger nematodes (Xiphinema). The lower PPN abundance in switchgrass may be due to its higher AMF associations, as AMF can provide protection against PPN through a variety of mechanisms. Fertilizer had minimal effects on AMF and nematode communities in both crops, possibly due to the relatively low levels of nitrogen added in this experiment. Overall, our study shows that management choices associated with perennial bioenergy cropping systems can influence belowground diversity and function.