Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Biological Science



First Advisor

Jason D. Hoeksema

Second Advisor

John S. Brewer

Third Advisor

Clifford A. Ochs

Relational Format



Various economic theories have been adapted to explain the evolutionary persistence of resource exchange mutualisms such as mycorrhizae. The ratio of resources exchanged is an important variable comto all these models. Measuring resource exchange ratios is the first step in testing the hypotheses predicted by these models and will provide insight into resource dynamics of mutualisms. We examined how the carbon, nitrogen and phosphorus resource exchange dynamics between Pinus radiata and an ectomycorrhizal fungus, Rhizopogon occidentalis, varied between native populations of Pinus radiata and over the first 64 weeks of the mycorrhizal mutualism. Using a mycocosm approach, the C:N and C:P exchange ratios were determined by comparing the amount of C respired by fungi and C assimilated in fungal biomass to the amount of N and P assimilated in plant tissues over a time period. Resource exchange was assessed at 8, 16, 32, and 64 weeks after inoculation for two Pinus radiata native populations. Resource exchange increased over time during the development of the mycorrhizal mutualism. Pine seedlings from the Cambria population transferred greater amounts of carbon to the ectomycorrhizal fungus, with the majority of this carbon being respired by fungal biomass. The ratio of resources exchanged did not vary over time or between pine populations, pointing to total resource fluxes as the potential mechanism behind changes in mycorrhizal fungal compatibility between populations of host plants.



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