The impact of a changing global N cycle on terrestrial ecosystems

Abstract

Nitrogen is an essential element of life. It is also one of the most abundant, making up approx. 78% of the Earth’s atmosphere. N is largely made up of inert atmospheric N2, less than 2% of all N is directly available for organisms. N2 first has to be fixed and converted to reactive nitrogen (Nr) before usage. N-fixing microorganisms provide the largest natural source of Nr. In the last 50 years, this source has been exceeded by anthropogenic Nr, mainly originating from synthetic N fertilizers. This has caused an major input of Nr into the global N cycle. Input of anthropogenic Nr will continue to rise, primarily driven by the increase in the human population in Asia. Nr plays a role in environmental issues like the greenhouse effect, smog forming, stratospheric ozone depletion, acid deposition, coastal eutrophication, and reduced diversity of water bodies and terrestrial ecosystems. Although the effects are predominantly detrimental, they differ greatly between terrestrial ecosystems and depend on many factors. In both agriculture and industry, the excess in N can be reduced by several measurements. The biggest challenge for the future is increasing the efficiency of N fertilizer use while decreasing the negative effects on the environment.