Recent studies have shown that human nitrogen additions to terrestrial ecosystems increase the terrestrial carbon dioxide uptake from the atmosphere. A new study published online this week in Nature Geoscience reports now that the climatic benefits from carbon sequestration are largely offset by increased nitrous oxide emissions, a further side-effect of human nitrogen additions to terrestrial ecosystems.
Human activities have more than doubled nitrogen inputs to the terrestrial biosphere since the 1860s. The two main causes for this are increased atmospheric nitrogen deposition from, for instance, fossil fuel burning, and the application of fertilizers in agriculture. Nitrogen is an essential nutrient for plant and microbial growth, and one of the key limiting nutrients in many natural ecosystems. The anthropogenic perturbations of the nitrogen cycle are known to affect the terrestrial sources and sinks of greenhouse gases such as carbon dioxide and nitrous oxide. These changes are potentially very important as they may significantly affect the climate system, but their magnitude is still unknown.