Summary The 20th century saw dramatic increases in agricultural productivity, largely through the development and application of pesticides, fertilisers rich in nitrogen and phosphorus, and advances in plant breeding and genetic technologies. In the last 15 years, however, many key crop yields have plateaued. Climate change, an ever‐increasing human population, depletion of global rock‐phosphorus and growing energy prices make current fertiliser production unsustainable and represent sizeable challenges to global food security. Many important crops form symbioses with arbuscular mycorrhizal fungi (AMF), and this has motivated the development of novel approaches in crop breeding and agricultural practices to support and promote AMF in agroecosystems. Arbuscular mycorrhizal fungal symbiosis can be high beneficial in crops and wider agroecosystems in many ways, including improved soil structure and resistance to pests. However, AMF colonisation does not necessarily translate directly into enhanced plant performance or crop yield, while land management practices that would encourage mycorrhiza–crop associations, such as low‐till or minimal chemical input often incur yield‐reducing trade‐offs. Synthesis. We draw on ecological knowledge of AMF to inform their role in agroecosystems, providing a balanced look at mycorrhiza–crop symbioses in terms of plant ecophysiology and the wider role of AMF in agroecosystems and ask the question: are AMF our sustainable saviours?

Highlights d We tested how aphid herbivory and increasing CO 2 affects wheat mycorrhizal function d Aphids reduced wheat C supply to mycorrhizal fungi. High CO 2 had no effect. d Transfer of fungal 33 P to plant was maintained regardless of aphids or high CO 2 d Mycorrhizal function is context dependent, affected by biotic and abiotic factors

Societal Impact StatementThe Earth's population is projected to rise to 9.7 billion by 2050 resulting in mounting pressure to increase agricultural yields in a sustainable manner. Arbuscular mycorrhizal (AM) fungi may be important players in this agricultural transition given their capacity to improve soil and plant health. Benefits gained by crops hosting AM fungi can be cultivar-specific and also affected by insect herbivory, although the combined effect of these factors remains unclear. Here, we show that, in an economically and socially significant tri-partite system, there is interplay between crop cultivar, AM colonisation and aphid herbivory on plant growth and nutritional status. Summary• Arbuscular mycorrhizal (AM) fungi are critical components of the rhizosphere across nearly all terrestrial biomes. AM fungi associate with most plants, including major crops, usually increasing plant access to soil nutrients and enhancing defence against pests and pathogens in return for photosynthetic carbon (C).