CONTEXT DEPENDENCE OF PLANT-FUNGAL INTERACTIONS
Understanding how environmental conditions mediate the outcome of biotic interactions is a key question in community ecology. Many studies in this area have focused on how environmental context affects competitive interactions between members of the same guild. However, less work has been done on the effects of environmental context on other interactions, such as mutualism or parasitism. This question is particularly interesting because changing environmental conditions have the potential to move mutualistic interactions along the mutualism-parasitism continuum and may be a source of evolutionary instability. Mycorrhizal symbiosis is often depicted as a biological market, with the plants trading photosynthetic carbon for fungal derived nutrients and water. Under such a scenario, changes in resource availability (e.g. through anthropogenic nitrogen deposition) may decrease the value of fungal services, and in some agricultural settings there is evidence that high levels of fertilization can select for strains of mycorrhizal fungi that may actually become parasitic, decreasing plant growth.