Dissertation Research: The Effects of Light and Arbuscular Mycorrhizae on Oak Savanna Plant Community Composition

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Arbuscular mycorrhizal fungi (AMF) are the most common kind of beneficial fungi associated with plant roots. This study tests the hypothesis that light availability and AMF interact to influence the composition of the remarkably diverse plant communities in Midwestern oak savannas. Plants in sunnier areas have greater needs for soil nutrients, and so may benefit more from AMF (or from highly active AMF species) than plants in shady sites. Plants in shady sites should either lack AMF or be associated with species having lower metabolic rates. Shifts in the kinds and numbers of fungal species along sun-to-shade gradients may thus have a profound effect on the identity and diversity of savanna plants. To test these ideas, we will first measure the distributions of plant species and AMF species as a function of light availability and soil texture in three Wisconsin savannas. The effects of AMF on understory plants will then be evaluated by applying fungicide to experimental field plots and documenting changes in plant composition over a two-year period relative to untreated plots. Finally, we will conduct experiments under greenhouse conditions to determine the effects of different AMF species on the growth of individual plant species when they are grown alone, and on the competitive ability of those same species when grown together.