Can mycorrhizal fungi indirectly affect plant-ant mutualisms?
Laird, Robert*,1, Addicott, John1, 1 Department of Biological Sciences, Calgary, Alberta, Canada
ABSTRACT- Plants provide a conduit through which below- and aboveground ecological processes can interact. For example, soil-dwelling arbuscular mycorrhizal ('AM') fungi trade soil nutrients for carbohydrates that their host plant produces during photosynthesis. This exchange alters the host plant's morphology and physiology, leading to a variety of positive and negative indirect effects on insect herbivores and pollinators. We tested the hypothesis that AM fungi can also indirectly affect insects involved in protection-for-food mutualisms, in which the insects (typically ants) protect their host plant from herbivory in exchange for food rewards in the form of extra-floral nectar. We manipulated the presence/absence of AM fungi in broad bean plants (Vicia faba L., Fabaceae) and found that plants with AM fungal associations produced fewer food rewards (i.e., fewer extra-floral nectaries) compared to plants without AM fungal associations. AM fungi are a strong carbon sink to their host plant, and these results suggest that the fungi preempt carbon that would otherwise be available for extra-floral nectar production. Future work will build on our results by testing the predictions that mycorrhizal plants should attract fewer mutualistic ants and suffer greater leaf damage from herbivores. Our results suggest that the costs and benefits of the mycorrhizal symbiosis must be considered from a multitrophic perspective. They also emphasize the importance of unifying the historically separate sub-disciplines of aboveground and belowground ecology.
Key words: trait-mediated indirect effects (TMIIs), belowground-aboveground interactions, fungus-plant-insect interactions
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