Perspectives on allelopathic disruption of plant mutualisms: a framework for individual- and population-level fitness consequences

Mutualisms with mycorrhizal fungi, pollinators, and seed dispersers are critical for plant survival and reproduction. However, mutualism effectiveness is highly sensitive to disturbance by environmental stressors. Allelopathy is often overlooked, yet likely important, as a potential stress on plant mutualism function. Allelochemicals can affect plant mutualisms by either directly interfering with the plant’s ability to produce resources and rewards for its mutualistic partners or by directly or indirectly altering the non-plant mutualist’s behavior. Here we explore the potential effects of allelochemicals on plant mutualisms. Since allelochemicals can reduce plant growth and carbon acquisition, we suggest that allelopathy could directly diminish: (1) carbon provisioning to mycorrhizal fungi, (2) flower, pollen, and nectar production for pollinators, and (3) fruit attractiveness to seed dispersers. Similarly, allelochemicals that directly affect mycorrhizal fungi functioning can reduce the flow of soil resources to their plant partner. Further, volatile allelochemicals or uptake of allelochemicals from the soil by the plant could alter pollen/nectar or fruit attractiveness and indirectly influence pollinator and seed disperser behavior. Finally, we explore the extent to which plant-produced chemicals could have a direct or indirect positive effect on plant mutualisms. We end using these questions to frame future avenues of research that could help to move studies of allelopathy into the broader ecological context of mutualisms.