Print PageSoil microbial communities have important direct and indirect effects on plants and other community members both above and below the soil surface. By influencing plastic plant traits, soil microbes have the potential to alter plant-insect interactions. Agricultural practices can have profound effects on soil microbial communities such as arbuscular mycorrhizal fungi (AMF), thus affecting both above- and belowground ecological interactions. We inoculated sterile soil with mycorrhizal communities collected from organically- and conventionally-managed farms and with a commercial AMF inoculum. We grew Cucumis sativus (cucumber) in these soils and measured plant growth and traits important in mediating interactions between insect herbivores and pollinators.
Results/Conclusions
Colonization by AMF was greater in organic than conventional farms, although commercial inoculum had the most vesicles. Farm AMF in general reduced seed germination and leaf size compared to commercial AMF and control, although treatments had no effect on either above- or belowground biomass. AMF increased leaf nutrients but had no effect on chemical defenses (cucurbitacins), possibly increasing susceptibility to aboveground herbivores. However, AMF from both organic and conventional farms increased cucurbitacins in roots, which may help defend against soil-dwelling herbivores. Male flower production was reduced by farm AMF compared to commercial AMF and control, but flower size and nectar production were unaffected. By reducing the number of flowers, farm AMF likely reduces attraction of pollinators, with a potentially negative effect on pollinator services. Overall, positive effects of the mycorrhizal symbiosis were not apparent, and effects on plant traits mediating interactions with herbivores and pollinators could reduce plant fitness. This suggests that both conventional and organic farming practices may select for non-beneficial AMF.
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