The effects of aphid herbivory upon barley root fungal and AMF communities and characteristics in an agricultural system. Aphid herbivory on barley root fungal communities

Arbuscular mycorrhizal fungi (AMF) form symbioses with the roots of most plant species, including cereals. AMF can increase plant nutrient uptake including nitrogen (N), phosphorus (P) and silicon (Si) as well as increase host resistance to other stresses. Plants may simultaneously interact with pests such as aphids, which can alter the proportion of plant roots colonized by AMF. However, it is unknown if aphid herbivory impacts the structure of AMF communities colonizing plants or the extraradical mycelium produced in the soil, both of which can influence the defensive and nutritional benefit a plant derives from the symbiosis. This study investigated the effect of aphid herbivory on plant and AMF characteristics in a conventionally managed agricultural system. As plants also interact with non-AM soil fungi, the non-AMF fungal community was also investigated. We hypothesised that aphid herbivory would depress plant growth, thus reducing intraradical AMF colonization, soil fungal hyphal density and the diversity of AM and non-AM fungal communities. We also predicted the abundance of some AMF families would relate to above-ground plant nutrition in the field. To test the effects of aphids, insect proof cages were used to inoculate field plots of barley with Sitobion avenae or no aphids. AMF specific and total fungal amplicon sequencing assessed root fungal communities after 46 days herbivory. Aphid herbivory did not impact above-ground plant biomass, but did increase N:P ratios. Whilst aphid presence had no impact on AMF intraradical colonization, soil fungal hyphal length density, or AMF community characteristics, there was a trend for aphid herbivory to result in increased vesicle numbers and the relative abundance of the AMF family Gigasporaceae. Aphid presence also increased the evenness of the total fungal community. The relative abundance of the most abundant AMF family, Glomeraceae, and the AMF physiological characteristics measured in the barley roots were negatively associated with stem and leaf biomass. The abundance of Archaeosporaceae was associated with stem and leaf Si, P and carbon levels. This study reveals that aphid herbivory can influence soil fungal communities and highlights relationships between AMF identity and above-ground crop nutrition in conventional agricultural systems.