The ability of forests to continue absorbing atmospheric CO2, and hence mitigating climate change, depends on the extent to which their productivity is limited by nutrients, with nitrogen (N) being particularly important in temperate and boreal regions. Fertilisation experiments offer an opportunity to directly determine whether atmospheric N input can contribute to alleviating N limitation. However, the majority of the experiments have normally considered soil N applications, which do not mimic changes in N deposition, as they exclude atmosphere-canopy exchanges, including direct foliar N uptake. In this context, the manipulation experiment established in a mature Fagus sylvatica L. forest in Italy represents a unique resource for advancing understanding on forest responses to global change. At this site, four different treatments have been carried out since 2015: control, canopy (30 kg ha-1 yr-1) and soil (30 and 60 kg ha-1 yr-1) N additions. Our goals are to: i) explore long-term (1940-2020) changes in tree growth and elucidate main drivers (climate vs. anthropogenic factors), ii) assess whether soil and canopy N additions lead to different dynamics in terms of growth and intrinsic water-use efficiency (the ratio between photosynthesis and stomatal conductance). For this purpose, dendrochronological analyses will be combined with the measure of δ13C, δ18O and δ15N in annual rings. Preliminary analyses indicate that tree growth has increased over the last 80 years, and that climate factors were the main drivers. On-going δ13C analyses will provide insight regarding the physiological mechanisms underpinning growth changes in relation to different ecosystem N dynamics (retention vs. loss pathways).