Herbivore-Driven Disruption of Arbuscular Mycorrhizal Carbon-for-Nutrient Exchange is Ameliorated by Neighbouring Plants

Durant, E. and Hoysted, G.A. and Howard, N. and Sait, S.M. and Childs, D.Z. and Johnson, D. and Field, K.J. (2023) Herbivore-Driven Disruption of Arbuscular Mycorrhizal Carbon-for-Nutrient Exchange is Ameliorated by Neighbouring Plants. Working Paper. SSRN Working Paper.

Abstract

Arbuscular mycorrhizal fungi colonise the roots of most terrestrial plants, forming a globally significant symbiosis which is typically characterised by bi-directional exchange of fungal-acquired nutrients for plant fixed-carbon. Mycorrhizal fungi can form networks belowground with potential to facilitate the movement of carbon, nutrients, and defence signals across plant communities. The importance of neighbours in the mediation of carbon for nutrient exchange between mycorrhizal fungi and their plant hosts remains equivocal, particularly when other competing pressures for host plant resources are present. We manipulated the carbon source and sink strengths of neighbouring pairs of host plants through exposure to aphids and tracked the movement of carbon and nutrients with isotope tracers across the mycorrhizal fungal networks. When the carbon sink strengths of both neighbouring plants were increased by introduction of aphids, plant carbon supply to extraradical mycorrhizal fungal hyphae was reduced, but mycorrhizal phosphorus supply to both plants was maintained. However, when the sink strength of only one of the neighbouring plants was increased by aphid herbivory, carbon supply to the mycorrhizal fungal hyphae was restored. Our results show that the loss of carbon inputs into extraradical mycorrhizal fungal hyphae from one plant may be ameliorated through the inputs of a neighbouring plant, demonstrating the responsiveness and resilience of mycorrhizal plant communities to biological stressors. We show that mycorrhizal nutrient exchange dynamics are better understood as community-wide interactions between multiple players rather than being driven by strict exchanges between individual plants and their symbionts.