There is an imminent socio-political and economic need to identify cost-effective mitigation strategies if we are to minimise the impact of climate change and ensure global environmental security. Forest ecosystems are considered as potential carbon (C) sinks under future climate forcing, as C inputs to plant biomass and soil are generally predicted to increase. However, a key determinant of C-sequestration efficiency is, among others, the availability and sustainability of other nutrients, including nitrogen (N). This presents great uncertainty in predicting the global capacity of terrestrial ecosystems to sequester C because there are major gaps in our understanding of the interactions and feedbacks between the C and N cycles. Interactions are further complicated when multiple climate factors are considered and increased microbial activity could serve to negate any C-sequestration as soil organic matter is mineralised at faster rates. This synthesis paper highlights the importance of N in forest ecosystem C-sequestration and identifies the mechanisms involved. We propose that a better mechanistic understanding on interactions between plant and microbial communities should be explicitly considered for the development of effective policy strategies for forest ecosystem C sequestration. ; Macdonald, Catriona A. Anderson, Ian C. Bardgett, Richard D. Singh, Brajesh K.