The ability of forests to continue providing important ecosystem services and mitigating climate change depends on their ability to cope with - and adapt to - global change components, such as more frequent climate extremes (specifically drought and heatwaves) and changes in atmospheric pollutants (namely carbon dioxide, CO2, and reactive nitrogen, N, compounds). The 2003 heatwaves cannot be considered as an exceptional event anymore, as prolonged summer droughts and temperatures anomalies are becoming more common and frequent across the whole European continent, due to the human-induced climate change. Frequent droughts and hot extremes are not the only challenge forests need to face. Since the industrial revolution, atmospheric chemistry has been altered, with steadily increases in CO2 concentrations (Ca), but also to changes in reactive N in the oxidised and reduced forms. While almost half of the CO2 emitted by fossil fuel combustion remains in the atmosphere (and hence contribute to global warming), reactive N compounds are deposited back to terrestrial and aquatic ecosystems, directly altering the N cycle, but indirectly also the carbon and water cycles. While N deposition (Ndep) could stimulate tree growth in a CO2 richer word, excess N could result in forest dieback, through soil acidification and nutrient imbalances but also by making trees more vulnerable to climate extremes. How do these global change components interact and affect forest carbon, water and N cycling? What are the ecological mechanisms involved? Are those mechanisms synchronized (in space and time) at tree and ecosystem scale? Answering these questions is of paramount importance to reduce the uncertainties on the sustainability of the CO2 fertilisation effects on forest carbon sink and hence, to predict future forest function and climate mitigation potential. In order to answer these fundamental questions, NEXTRES will consider 12 forests along a climate and N deposition gradient (from 3 to 42 kg ha-1 yr-1, see experimental sites here) in Europe, and four of the most widespread species in European forests: Fagus sylvatica, Quercus spp., Picea abies, Pinus sylvestris. Forests sites will be selected within established networks, namely ICOS and/or Fluxnet (for the ecosystem scale measurements of carbon and water fluxes with eddy covariance technique) and ICP Forests (for atmospheric nitrogen deposition). NEXTRES will complement existing data with dendroecological data (growth, stable carbon, oxygen and nitrogen isotope ratios), allowing to elucidate physiological mechanisms underpinning response to global change drivers from the multi-decadal to the intra-annual resolutions. Expected impacts of NEXTRES include not only the advancement of scientific knowledge and education; progress on the complex topic of forest response to global change drivers is also crucial to support data-based policies towards the ambitious goals set within the Paris Agreement and European Green Deal of a climate neutral Europe by 2050.