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 initiate changes 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, ecosystem processes and species assemblages, cannot accommodate easily the range of interactions between nitrogen acid 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 ecosystems and how these rates affect population dynamics of individual species and trophic relationships. Without this information, predictions of biological effects of enrichment ape difficult to make.