Soils contain the largest fraction of terrestrial carbon (C). Understanding the factors regulating the decomposition and storage of soil organic matter (SOM) is essential for predictions of the C sink strength of the terrestrial environment in the light of global change. Elevated long-term nitrogen (N) deposition into forest ecosystems has been increasing globally and was hypothesized to raise soil organic C (SOC) stocks by increasing forest productivity and by reducing SOM decomposition. Yet, these effects of N deposition on forest SOC stocks are uncertain and largely based on observations from high dose-N fertilization experiments. Here, I present a synthesis of results from three studies aiming at elucidating the effects of long-term N deposition on SOC stocks and fluxes in temperate conifer forests. In two of the studies, short N deposition gradients occurring naturally in forest edges were used to study the effects of varying N deposition load on SOC stocks and fluxes as well as on the temperature sensitivity of SOM respiration. In a third study, the effects of 20 years of continuous experimental N addition (35 kg N ha-1 year-1) on soil C budget were investigated. Our general hypotheses were that elevated N deposition will: i) increase SOC stocks owing to positive effect of N on litterfall C inputs combined with negative effect on SOM decomposition regardless of negative effects on belowground C inputs by roots and associated mycorrhiza; ii) reduce the temperature sensitivity of SOM heterotrophic respiration. The five forest edges investigated exhibited N deposition gradients decreasing from the edges toward the interior of the stands. Thus, increasing distance from the edge was used as proxy for decreasing N deposition. At the two edges receiving intermediate-N deposition rates (≤ 23 kg N ha-1 year-1), forest floor SOC stocks tended to decrease with distance from the edge while a decade of experimental N additions insignificantly increased the size of the humus (H) layer providing weak evidence for some positive effect of N deposition on SOC stocks. The three edges receiving higher N deposition rates (> 29 kg N ha-1 year-1) were N-saturated where SOC stocks in the top soil were either unchanged or negatively affected by elevated N deposition. Similarly, forest floor SOC stocks were unchanged following two decades of experimental-N additions. Aboveground C inputs by needle litterfall were generally not significantly affected by N deposition at the edge sites but tended to increase with increasing distance from the edge in two of the N-saturated sites. The experimental N additions resulted in reduced C inputs by foliar litter relative to control concomitant with reduced tree and moss growth. At three edges, fine-root biomass tended to increase with distance from the edge while over a decade of N additions reduced the means of fine-root biomass, ectomycorrihizal (EM) mycelial production and species composition insignificantly compared with control suggesting reduced belowground C inputs under elevated N deposition. At two edge sites, forest floor C outputs by respiration tended to decrease with decreased forest floor C/N and distance from the edge indicating positive effect of elevated N deposition on SOC sequestration. Correspondingly, N-enriched litter incubated in litterbags had significantly lower late-stage decomposition rates compared with control litter. However, potential respiration of forest floor and mineral soil was overall unaffected by the experimental N-additions. A temperature treatment of forest floor samples taken from one edge site revealed decreasing respiration rates and temperature sensitivity (Q10) of labile and recalcitrant SOM with increasing forest floor C/N ratio. I conclude that N deposition at rates typical to agriculturally intensified regions in north-western Europe may reduce the decomposition rate of SOM thereby positively affecting SOC sequestration but at the same time above- and belowground C inputs also decrease resulting in no change in SOM stocks. Moreover, elevated N deposition may reduce the potential positive feedback of SOM decomposition on global atmospheric CO2 concentrations. These results have implications for modelling the carbon sink-strength of temperate forests under global change.