Adam Frew & Jodi N. Price
Most of the plants on land have a close relationship with a group of symbiotic fungi called arbuscular mycorrhizal (AM) fungi. Simply explained, AM fungi typically provide their hosts with nutritional benefits and can also affect plant defences against insect herbivores. Almost all of these plants in nature will be attacked by one, if not many, species of insect herbivore. Therefore interactions between AM fungi, plants and herbivorous insects are globally pervasive, and are key to many ecosystem processes.
We are now beginning to experience the effects of rising atmospheric CO2 concentrations, which are predicted to continue to rise. Research efforts are increasingly enhancing our understand of how elevated CO2 concentrations will impact plants, plant-herbivore interactions and AM fungal-plant interactions. Comparatively, we have very little understanding of how the relationship between these three important players, AM fungi, plants and insect herbivores, will function in a high CO2 world.
Here, we highlight some of the general effects of CO2 enrichment on bipartite interactions between AM fungi and terrestrial plants, and between plants and their herbivorous enemies. We point out the complexity of these interactions, and that mediating mechanisms underpinning AM fungal-plant-insect herbivore relationships exposed to high CO2 can act antagonistically. Thus trying to predict the potential outcomes for these tripartite interactions is challenging.
We urge researchers to address the pressing need for studies which directly investigate how elevated CO2 concentrations impact mycorrhizal mediated plant-herbivore interactions. These gaps in our knowledge can be addressed with appropriately designed experimental studies coupled with observational fieldwork built around key priorities. As studies begin to inform our greater understanding of the functioning of this tripartite relationship, we will gradually become better equipped to anticipate the challenges that a high CO2 world will present.