Are rising carbon dioxide and nitrogen deposition a joint threat to biodiversity globally?

Whether rising carbon dioxide concentrations affect terrestrial species diversity around the globe is, surprisingly, almost unstudied. A 24-year field experiment shows that adding nitrogen to grassland plots reduces species richness, and that increasing the level of carbon dioxide amplifies this effect, tripling the reductions caused by nitrogen addition. In the long term, increased carbon dioxide reduces the number of plant species by worsening the effects of nitrogen pollution.