I'm entering my last undergraduate degree and also have to do a thesis, coincedently i'm researching mycorrhizas.
Here is some ideas to build on: From my limited reading on Mycos so far i know they work to sequester immobile nutrients, mainly P, from the soil and make them increasingly available to the host plant. On their own plants naturally produce organic acids in root exudates to free up immobile nutrients. Perhaps mycorrhiza colinization has an effect on organic acid production in the plant since it takes that P assimilation burden away from the plants, there's an experiment. In addation, organic acid production by plants could change microbial composition in the rhizosphere. So maybe do an experiment that includes organic acids, mycorrhiza and other microbes. This is all just speculation, i have no idea if anything has been done, just ideas. Good luck