The embarrassment of riches: atmospheric deposition of nitrogen and community and ecosystem processes.

Anthropogenic sources of nitrogen have exceeded, and will continue to exceed, annual inputs of nitrogen produced by natural processes. Nitrogen enrichment may in plant tissue chemistry and microbial decomposition processes, as well as affecting rates of herbivory, all of which may be expected to result in changes in plant species assemblages Individual concepts, such as nitrogen saturation and critical load, used to describe the effects of enrichment on soil, community, ecosystm processes and species assemblages, cannot accomodate easily the range of interactions and different environmental processes. A number of approaches need to be used in tandem. Major gaps in knowledge are rates of transfer of anthropogenic nitrogen within and between different ecosystem and how these rates affect population dynamic of individual species and trophic relationships. Without this information, predictions of biological effects of enrichment are difficult to make.