Here the authors present results of the first multi-decadal experiment to examine the impacts of chronic, experimental nitrogen addition above ambient atmospheric nitrogen deposition. This total input rate is comparable to terrestrial nitrogen deposition in many industrialized nations. The researchers found that this chronic low-level nitrogen addition rate reduced plant species numbers by 17% relative to controls receiving ambient N deposition.

Rates of atmospheric deposition of biologically active nitrogen (N)are two to seven times the pre-industrial rates in many developed nations because of combustion of fossil fuels and agricultural fertilization. They are expected to increase similarly over the next 50 years in industrializing nations of Asia and South America. Although the environmental impacts of high rates of nitrogen addition have been well studied, this is not so for the lower, chronic rates that characterize much of the globe. Here we present