This session will examine how soil biota indirectly alter aboveground plant-insect interactions and plant competition. Plant interactions with soil organisms can have large effects on plant phenotype. For example, earthworms and detritivores alter plant phenotypes through the mobilization of nutrients, fungi, and bacteria in the rhizosphere. Nematodes and root herbivores often reduce plant fitness through feeding on root tissue, and mycorrhizal fungi increase plant fitness through increased nutrient uptake. Resulting changes in plant phenotype can alter interactions between plants and aboveground herbivores, pollinators and competitors. This session explores patterns and mechanisms of such multi-trophic below- and above-ground interactions. Can we predict the outcome of these multi-level species interactions by combining our knowledge of distinct pairwise interactions? For example, if mycorrhizal fungi increase plant biomass and fitness, does this directly translate into increased fitness or biomass for herbivores feeding on these larger plants? If the outcomes of these pairwise interactions are not additive, then what are the underlying mechanisms through which soil biota change plant-herbivore, plant-pollinator, or plant-plant interactions? For example, do changes other than simple increases in plant size (such as disproportionate changes in plant defense) occur in plants associated with mycorrhizal fungi, in turn altering fitness of herbivores feeding on host plants? Speakers will focus not only on the intersection of soil biota, plants, and aboveground interactions, but also on the mechanisms through which soil biota alter many different aboveground plant interactions.