Abstract
Arbuscular mycorrhizal fungi (AMF) form symbioses with the roots of most plant species, including cereals. AMF can increase the uptake of nutrients including nitrogen (N) and phosphorus (P), and of silicon (Si) as well as increase host resistance to various stresses. Plants can simultaneously interact with above-ground insect herbivores such as aphids, which can alter the proportion of plant roots colonized by AMF. However, it is unknown if aphids impact the structure of AMF communities colonizing plants or the extent of 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 aphids on the plant-AMF interaction in a conventionally managed agricultural system. As plants also interact with other soil fungi, the non-AMF fungal community was also investigated. We hypothesized that aphids would depress plant growth, and reduce intraradical AMF colonization, soil fungal hyphal density and the diversity of AM and non-AM fungal communities. To test the effects of aphids, field plots of barley enclosed with insect proof cages were inoculated with Sitobion avenae or remained uninoculated. AMF specific and total fungal amplicon sequencing assessed root fungal communities 46 days after aphid addition. Aphids did not impact above-ground plant biomass, but did increase the grain N:P ratio. Whilst aphid presence had no impact on AMF intraradical colonization, soil fungal hyphal length density, or AMF community characteristics, there was a trend for the aphid treatment to increase vesicle numbers and the relative abundance of the AMF family Gigasporaceae. Contrary to expectations, the aphid treatment also increased the evenness of the total fungal community. This suggests that aphids can influence soil communities in conventional arable systems, a result that could have implications for multitrophic feedback loops between crop pests and soil organisms across the above-below-ground interface.
Highlights
Arbuscular mycorrhizal fungi (AMF) form obligate symbioses with the roots of c. twothirds of land plant species, including agriculturally important cereals (Smith and Read, 2008; Fitter et al, 2011)
Current knowledge of how AMF respond to aphids sharing the same host plant is limited to the impact on AMF colonization (Babikova et al, 2014; Vannette and Hunter, 2014; Maurya et al, 2018; Meir and Hunter, 2018a)
Whilst the majority of plant biomass and nutrition, and AMF physiological traits were not influenced by aphid treatment (Table 3), aphid treatment significantly increased the stem N:P ratio by 5.4% (Table 3), and there was a near significant increase of 8.9% (P = 0.052) of the grain N:P ratio
Summary
Arbuscular mycorrhizal fungi (AMF) form obligate symbioses with the roots of c. twothirds of land plant species, including agriculturally important cereals (Smith and Read, 2008; Fitter et al, 2011). The bottom-up effect of below-ground AMF on the performance of above-ground herbivores such as aphids can range from positive to negative (Gange and West, 1994; Wurst et al, 2004; Ueda et al, 2013; Simon et al, 2017; Wilkinson et al, 2019) These impacts on aphid performance likely occur because of alterations to plant defense and nutrition due to the AMF symbiosis (Wurst et al, 2004; Meir and Hunter, 2018b) and can depend on the level of AMF colonization of the host plant (Tomczak and Müller, 2017; Maurya et al, 2018; Meir and Hunter, 2018a). Current knowledge of how AMF respond to aphids sharing the same host plant is limited to the impact on AMF colonization (Babikova et al, 2014; Vannette and Hunter, 2014; Maurya et al, 2018; Meir and Hunter, 2018a)
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