Net carbon sequestration by terrestrial vegetation is countering the effects of anthropogenic C emissions and tropical deforestation. The deposition of reactive N originating from anthropogenic emissions and intensive agriculture has long been suggested as a key determinant of this sequestration activity, but a lively debate has emerged on the magnitude of such an effect and the mechanisms involved, with important implications for future environmental policies. The proposed session will compare the evidence coming from different fields; both experimental and modelling studies will be welcome.