Forest trees have the potential to serve as substantial sinks for rising atmospheric CO2 levels if nutrient limitations characteristic of most forest soils can be overcome. Increased carbon availability may stimulate a symbioltic relationship that exists between tree roots and soil fungi with enhanced nutrient acquisitions by trees as a result. My work investigates the possibility that physiological differencces between the two major types if symbiotic soil fungi may lead to differential responses of tree species to CO2 enrichment. Two of the major differences hypothesized to exist between the symbioses lie in 1) the amount of carbon acquired by the tree that must be allocated towards support of the fungal partner, and 2) the amount of nutrients taken up from the soil by the fungus and released to the host tree. Radiotracer techniqueswill be used to measure carbon allocation and phosphorus uptake in tree species engaging in the two types of symbioses and growing at three levels of CO2 enrichment. An understanding of mechanisms underlying the responses of forest trees to environmental change will improve our ability to predict forest ecosystems behavior in a CO2-enriched world.
