Nitrogen deposition can enhance above ground carbon sequestration, but most of the carbon in boreal forest soils are stored in soils. A higher above ground growth enables a higher input of above ground litter to soils, potentially increasing soil carbon stocks. However, a large flux of carbon is entering soils through roots, where it is used to produce and maintain root biomass, as well as exported into microbial biomass such as ectomycorrhiza. Root and microbial biomass production and turnover is an important source of soil carbon, but labile carbon in the root zone is also driving decomposition processes. In this project, we use the Åheden long-term low to high N addition rate experiment to study the consequence of different rates of N input on the soil C balance. We combine above ground flux measurements including the input of above ground litter and output of CO2 by respiration, and below ground measurements on fine-root and ectomycorrhizal fungal biomass production to understand how different rates of nitrogen addition influence the amount, form, and location of carbon inputs to soils, with the overall goal to understand how N deposition influence the boreal forest carbon sink.