Collaborative Research: Price determination in ectomycorrhizal symbioses

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Many pairs of species are involved in mutually beneficial exchanges. One of the most widespread and ecologically important types of these mutualisms in nature are associations between fungi in the soil and the roots of plants, known as mycorrhizae (fungus-roots): the fungus exports mineral nutrients such as phosphorus and nitrogen to the plant and the plant exports sources of energy based on carbon to the fungus. However, as in other types of exchanges, the actual net benefits to each partner in these associations can depend upon the current costs of exports and value of imports. The associations may even grade into parasitism of one partner on the other and fall apart when, for example, a rise in the concentration of nitrogen and phosphorus in the soil makes export from the fungus superfluous to the plant. One difficulty in understanding and predicting when resource exchanges between organisms will be truly beneficial is the problem of comparing apples to oranges: how does one compare the cost of exporting one element, such as carbon, to the benefit of importing a different one, such as nitrogen or phosphorus? This project will try to solve this problem by using economic models to calculate a "price of resource exchange" between species. Laboratory experiments will measure resource exchange prices between the Monterey pine and eight of its mycorrhizal fungi and show how those prices vary over time, as abundances of the resources change, and between the species of fungi. This will test whether scientists can use economics to understand and predict the interactions between species as different as fungi and plants.The project will also help us understand how economically important trees such as the pine respond to changes in soil fertility, and help us more accurately model global cycles of elements such as carbon and nitrogren. In addition, the project will train graduate and undergraduate students from groups that are under-represented in science, and work with teachers in two local high schools to teach younger students about the vital role of fungi in the soil, through a field trip and a year-long experiment right in the classroom.