Symbiotic arbuscular mycorrhiza amplifies herbivory interactions and decreases the energy of floral nectar

Abstract

Background and Aims Arbuscular mycorrhizae (AM) are crucial in terrestrial ecosystems, exchanging nutrients for carbon with plants and potentially modulating events on the soil surface by making nutrients available to herbivores and pollinators. The quadruple interactions between mycorrhizae, plants, herbivores, and pollinators are a complex phenomenon as a whole; a detailed understanding of their synergistic or antagonistic effects remains a pending research challenge. Methods To comprehend these multiple interactions, AM were inoculated into Nicotiana tabacum and the magnitude of the symbiotic effect on floral (nectar, floral morphology, floral count) and vegetative (plant size) characteristics was evaluated, as well as the effect on pollinator visitation rate and herbivory intensity. Results We support the hypothesis of a symbiotic effect with a tendency toward antagonism, resulting in negative consequences for the plant. Symbiosis decreased the synthesis of floral nectar, and consequently reduced the energy content of floral nectar, without producing any effect on the pollinator visitation rate. An increase in herbivory rate was observed in mycorrhizal plants, indicating that belowground symbiotic relationships enhanced surface-level antagonistic interactions. Conclusion Mycorrhiza negatively influenced the plant's metabolic activity, leading to repercussions for energy investment in both pollinator manipulation resources (nectar) and defense and protection against herbivores.