Effects of N, P, and C additions to the belowground processes of white oak and sugar maple

Global climate changes, such as increasing nitrogen deposition and CO₂ concentrations, are impacting temperate deciduous forests of the lower Great Lakes region, yet the effects of these changes on soil processes are not fully understood. In forest ecosystems, the largest carbon flux influencing net ecosystem productivity is soil CO₂ efflux, which is a product of both autotrophic and heterotrophic respiration.  Consequently, the effect of global climate changes on terrestrial ecosystems may be greatly influenced by the response of belowground processes.  This study examined the effects of nitrogen, phosphorus, and carbon additions to belowground processes associated with white oak and sugar maple in a field and mesocosm setting.  The study site was located at the Ameriflux site in Southern Indiana and treatments have been applied for three growing seasons.  Treatments were applied in a factorial design and dissolved in water to simulate wet deposition.  Preliminary results from the third year of treatment show strong species-specific interactions.  Soil respiration was increased in maple plots by phosphorus additions, while oak plots were increased by carbon additions.  Similarly, nitrogen and phosphorus additions increased fine root biomass, but had little effect on oaks.  Soil carbon content was decreased by phosphorus additions and the soil microbial biomass was not significantly altered by any resource addition.  These results show that belowground processes are differentially altered by tree species and more research is needed to make predictions of the long-term effects of global climate changes in this ecosystem.