Preferential Allocation of Photosynthate toward Better Mutualists, Spatial Structure, and the Maintenance of the Arbuscular Mycorrhizal Mutualism

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Arbuscular mycorrhizal (AM) fungi form beneficial associations with the roots of most plant species, including most crop plants. These fungi increase plant access to immobile soil minerals and receive plant carbohydrates in return. While this interaction can be mutually beneficial between plants and fungi, the extent to which the fungi increase plant growth varies across soil environments and fungal isolates. Moreover the benefit has been observed to increase and degrade over time. Currently, there is little basis for predictive understanding of these dynamics. Recent work has demonstrated that plants can allocate their carbohydrates preferentially toward the most beneficial fungus. This preferential allocation allows the effective fungus to increase in the face of competition from non-beneficial fungi provided that there is sufficient spatial separation between the fungi within a plant's root system. Preferential allocation may form a foundation on which to understand the persistence of beneficial fungi and change in their abundance over time. The proposed work will test resource triggers and environmental dependence of preferential allocation and test patterns of preferential allocation across plant and fungal species. Finally, fungal population response to manipulation of spatial mixing of the fungi within the plant root system will be evaluated. These results will be used to develop predictions for changes in abundance of beneficial fungi across environmental gradients. The proposed research will train undergraduates, graduate students and postdoctoral scientists in techniques used to measure and manipulate beneficial AM fungi. In addition, this research will create opportunities for independent undergraduate research. In particular, an experiment testing how mycorrhizal fungi may benefit restoration of a native prairie on the campus of Indiana University will be initiated as part of a non-majors course in environmental biology. Students will thus be exposed to multiple aspects of ecological research related to this project.