A CORRELATIVE EVALUATION OF NITROGEN CYCLING IN THE FOREST ECOSYSTEMS OF THE EC PROJECTS NITREX AND EXMAN

Results from two EC ecosystem manipulation projects (NITREX and EXMAN) were integrated by a correlation analysis. The analysis focused on ambient nitrogen input and output and on the nitrogen concentrations in various compartments of the ecosystems. The dataset included 12 sites (11 coniferous forests and one alpine vegetation) covering a range of atmospheric nitrogen inputs from 3 to 60 kg N ha(-1) year(-1). Nitrogen input by precipitation and by throughfall were highly positively correlated, although the regressions differed for sites at which NO3- deposition dominates compared with sites at which NH4+ dominates. In general, nitrogen concentrations in needles, in needle litterfall and in the organic layer, as well as in drainage, were more closely correlated to nitrogen input in precipitation than throughfall. Variations in nitrogen concentrations in needles, in needle litterfall and in the organic layer explained 96% of the variation in nitrogen output.