"Reactive forms of nitrogen (N) from anthropogenic sources led to a doubling of the available N pool worldwide, with harmful consequences for human health and the environment.The solution of the N problem can only comes from an integrated approach, both in relation to the assessment of the biogeochemical and ecological interactions, and in relations to emissions abatement strategies. In this challenge, Europe has a leadership position, as testified by the numerous scientific networks, working groups and activities on the topic.The project REAL TUNE aims at being part of this multidisciplinary approach to the complexity of the N problem.Lichens are among the most sensitive organisms to NH3 pollution at the ecosystem level. Several studies have investigated the relationships between lichens and N, but the current knowledge about the ecological variables influencing lichen physiology cannot explain lichen behaviour in nature completely. N tolerance resulted to be modulated by cation exchange capacity, interaction with the carbon metabolism and polyamines. Our working hypothesis is that enzymatic pathways of the primary and secondary metabolism are deeply involved in the processes that provide N tolerance. To check it, protein expression, enzymatic activity of GS/GOGAT and GDH, and the role of polyamines as a sink for ammonium will be examined in two lichen species with a markedly different N sensitivity.Moreover, physiological response to N and pH changes separately, the different role of the single bionts in N response, and the metabolic and physiological effects of long-term exposures to N in a Mediterranean environment will be analysed in order to answer some important questions on lichen symbiosis and ecology.Besides its scientific value, we think that REAL TUNE, linking physiological mechanisms and ecological impacts of increase availability of reactive N, can provide suitable tools for N management and environment protection."