The availability of water and nitrogen and its partitioning between organisms are central factors for growth and development of forest ecosystems. However, the physiological and molecular processes responsible in the participating organisms for the partitioning of water and nitrogen as well as the interaction of these processes are in generell only poorly understood and have not been studies in detail in beech-dominated deciduous forests. Central aims of this research project are (a) the characterisation and quantification of the processes contributing to the competition for water and nitrogen in beech-dominated forests and (b) the identification of the regulatory mechanisms involved. The results of these studies will not only provide an improved system understanding, but will also be used for the improvement and validation of a process-oriented model to simulate changes in competition for water and nitrogen in beech-dominated forests under changing environmental conditions, i.e. reduced water availability and increased N-deposition. For this purpose, an experimental design is envisaged that combines exploratory field investigations with experimental field approaches, studies in lysimeter systems, investigations in microcosms in a climate-controlled greenhouse and phytotrons under controlled conditions, as well as laboratory experiments.