Root-associated fungi mediate plant-insect interactions in soil

Root-associated fungi are ubiquitous among plants and they are vital for plant growth and defense against pathogens and herbivores. Previous studies have consistently (4 out of 5 studies) revealed negative effects of mycorrhizal infection on root herbivores. Compared to the mycorrhizae, other endophytic fungi in plant roots were largely ignored until recently, in spite of their widespread occurrences in many ecosystems. Recent studies reveal that these non-mycorrhizal endophytic fungi are also likely to enhance nutrient acquisition and induce plant systemic resistance against other organisms. In this study, we manipulate different associations of mycorrhizae and endophytic fungi in grass in the greenhouse; and to investigate how endophytic fungi interact with mycorrhizae to influence overall plant performance and defense against root herbivores (Japanese beetle, Popillia japonica).  Our first hypothesis is that root-associated fungi can enhance plant nutrient acquisition and thus increase plant palpability to insect. Our alternative hypothesis is that root-associated fungi can induce plant systemic resistance, reducing the performance of P. japonica. Twenty-five morphospecies of endophytic fungi were isolated from roots of Kentucky bluegrass in March 2014. Kentucky bluegrass (Poa pratensis) was planted in the greenhouse and received one of six fungal treatments: single mycorrhizal species, mixed native mycorrhizal community, single endophytic fungal species, mixed native endophytic fungal comunity, combined mycorrhizal and endophytic fungi, and no-fungi control for a total of 240 pots (half receiving one third instar P. japonica larva). Preliminary data show that single mycorrhizal treatments significantly enhanced plant growth. We will discuss the response of P. japonica to different microbial treatments in relation to measured differences in root nutrient (N and P) and secondary metabolic (Phenolic) contents to address the plant nutrition and defense hypotheses.