Effects of a belowground mutualism on an aboveground mutualism

Studies of multitrophic interactions between below- and aboveground communities have generally focused on soil organisms and antagonists of plant shoots and leaves (herbivores). Despite the widespread occurrence of plant mutualists below- and aboveground which can occur on the same host plant, the potential for interactions between them has not been considered. Here we demonstrate that aboveground plant mutualists, insect pollinators, are strongly influenced by belowground plant mutualists, arbuscular mycorrhizal fungi. The presence of arbuscular mycorrhizal fungi in the roots of Chamerion angustifolium increased pollinator visitation and per cent seed set of this plant in the field by up to two times compared with non-mycorrhizal plants. We propose that interactions between belowground and aboveground mutualisms are widespread and may play important functional roles in populations and communities.