The influence of nitrogen availability on plant cover was investigated. The field nitrogen availability was determined along with several environmental parameters and plant species. The nitrogen use strategies of the plant species were also analyzed based on nitrate reductase and glutamine synthetase activities, leaf NO-3, NH+4 and malate concentrations, and on the variation of these parameters in space and over time. It was observed that shifts in soil nitrogen concentration, due to nitrogen deposition, industrial activities or agricultural practices, influence plant species and modify successional trajectories or ecosystem responses in changing environments in different ways.