Many forest ecosystems in Europe and North America have suffered from soil acidification and ecosystem eutrophication as a result of anthropogenic emissions of SO2, NOx and NH3. Sulphur (S) and nitrogen (N) deposition are important drivers of the terrestrial carbon (C) and N cycling. While most recent research has focused on the impacts of N deposition on C cycling, there is evidence that acidification (from either S or N deposition) may also impact on a range of key processes, including suppression of litter decomposition. Thus, understanding of soil C and N processes under changing deposition is needed for future prediction whether forest soils will act as a carbon sink or source. In addition, acidity changes in forest ecosystems have a strong confounding influence on ecosystem sensitivity to eutrophication, with acidification accelerating N saturation, and recovery potentially resulting in reversion to N limitation. However, over the last two decades transport of dissolved organic matter (DOM) from terrestrial to aquatic ecosystems has increased throughout much of Europe, with implication for the terrestrial C balance, aquatic ecosystems functioning, water treatment costs and human health. A number of studies have argued that the decline in S deposition has been the main driver of DOM increase.SLAvONIC aims to fill the gap in understanding of the combined effects of S and N deposition on altering C and N cycling in forest soils. In particular, the project will examine whether there has been a shift in the relative balance of soil N and C accumulation, versus soil losses in either (dissolved) organic or (dissolved or gaseous) inorganic forms. A set of replicated acidity/N availability manipulation experiments in beech and spruce forests will be undertaken in an area of formerly high S/N deposition. Obtained results will be used for development of a model of C and N cycling to predict future changes in ecosystem C and N balances.