Experimentally Testing Effects of Mycorrhizal Networks on Plant-Plant Interactions and Distinguishing Among Mechanisms

Abstract

Plants of the same and different species are often linked by common mycorrhizal networks (CMNs), and there is substantial disagreement in the literature about whether these linkages have important effects on plant-plant interactions, beyond simply providing mycorrhizal inoculum. Here, I attempt to reconcile opposing viewpoints by reviewing available evidence for three distinct mechanisms by which CMNs can affect plant-plant interactions. I also analyze the details of manipulative field experiments that have been conducted to test CMN effects on plant-plant interactions, and make recommendations for the kinds of future studies that will be most useful in moving forward. I argue that few experiments have unequivocally tested whether CMNs have unique effects on plant-plant interactions, and that these experiments have largely been ignored in favor of debates about the magnitude of resource flows (especially carbon) from plant to plant through CMNs. I suggest that progress on the debate will only be made through more thorough testing of alternative mechanisms besides plant-to-plant carbon flow, especially coupled with experimental manipulations of CMNs to test for consequences on specific aspects of plant community ecological processes.