DISSERTATION RESEARCH: Plant interactions across common mycorrhizal networks

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This investigation concerns the role of common mycorrhizal networks (CMNs) "fungus interconnections among plant root systems" in plant competition belowground. CMNs are formed by generally beneficial, root-inhabiting fungi called "arbuscular mycorrhizal fungi". Plants feed these fungi some of the sugar they produce by photosynthesis, and in return, the fungi take up and provide the plants with key mineral nutrients such as phosphorus and nitrogen. Once connected to a host plant's roots, the fungi forage throughout the soil and may encounter root systems of other plant species with which they additionally associate without preference, creating a network. The major question this raises is whether all plants connected to the network share mineral nutrients equitably or if mycorrhizal fungi disproportionately donate mineral nutrients to host plant species that provide them the most sugar. The researchers utilize tallgrass prairie species for their research, Big Bluestem and Canada Wild Rye. Tallgrass prairie is an endangered ecosystem in North America and prairie restorations often involve sowing the study species together. Understanding how CMNs affect interactions between these plant species might inform restoration management practices such as tillage, which can disrupt CMNs. Besides its relevance to prairie restoration, this research will engage Miami inner-city middle school students and university undergraduates from underrepresented groups. The researchers will investigate competition as mediated by CMNs between a tallgrass prairie dominant grass, Big Bluestem (Andropogon gerardii) and a less common species, Canada Wild Rye (Elymus canadensis). If Big Bluestem is able to obtain mineral nutrients disproportionately and thereby suppress the growth of Canada Wild Rye, then CMNs may contribute to Big Bluestem's dominance, influencing prairie community composition. The researchers will utilize a rotated conetainer method in the greenhouse to isolate and reveal the effects of CMNsby severing them. The proposed work will determine the effects of CMNs on the relative strengthsof intra- and interspecific competition and consequent size hierarchy development. The studentwill investigate if large carbon donation to CMNs elicits high mineral nutrient transfer frommycorrhizal fungi by using carbon stable isotope ratios to compare carbon supplied by theseC4 and C3 grasses to their leaf mineral nutrient contents in monoculture and mixture. Finally,if severing CMNs alters the fungus community on root systems, this will be investigated through DNA barcoding.