University of British Columbia, British Columbia, Canada
Abstract: Most angiosperms, and nearly all crop species, form belowground relationships with mycorrhizal fungi, typically AMF (arbuscular mycorrhizal fungi). The mechanisms by which AMF-plant relationships influence plant and community traits is still being worked out, but it is clear that the presence of AMF alleviates phosphorus and water limitation, positively impacting plant growth and even changing plant community composition. However, less is known about how plant-mycorrhizal relationships might indirectly influence aboveground ecological interactions such as those mediated by pollinators. To address this knowledge gap, we performed a literature search and meta-analysis of studies to examine the outcome of mycorrhizal manipulation experiments (largely AMF inoculation although our dataset also includes studies of fungal exclusion treatments) on plant traits associated with pollination, especially flower size and number (floral display), nectar quantity and chemistry, pollinator visitation and the composition of the pollinator community. In addition to floral traits, we collected information about the experimental design, including whether the fungal associates were added through inoculation or eliminated using fungicide, whether the plant species was a crop or wild plant, and whether the study took place in a greenhouse or field setting. We found that mycorrhizal inoculation was associated with a two-fold increase in the size of floral display traits such as flower size and flower number. Only a handful of studies used fungal exclusion to examine the effects of AMF on floral traits, and on average these studies exhibited a reversal in the direction of the effect, suggestion that fungal exclusion and AMF inoculation are not equivalent ways of exploring the role of mycorrhizal interactions on plant traits. Our results highlight the potential for relationships with mycorrhizal fungi to play an important, yet underrecognized role in aboveground ecological relationships mediated by pollinators. With prophylactic applications such as fungicidal seed coats playing an increasingly common role in agricultural management, our study highlights the unexpected ways in which fungi can influence plant ecological interactions in natural and agricultural systems.
