Planetary Homeostasis of Reactive Nitrogen Through Anaerobic Ammonium Oxidation

The availability of nitrogen (N) is crucial for both the productivity of terrestrial and aquatic ecosystems globally. However, the overuse of artificial fertilizers and the energy required to fix nitrogen have pushed the global nitrogen cycle (N-cycle) past its safe operating limits, leading to severe nitrogen pollution and the production of significant amounts of greenhouse gas nitrous oxide (N2O). The anaerobic ammonium oxidation (anammox) mechanism can counteract the release of ammonium and N2O in many oxygen-limited situations, assisting in the restoration of the homeostasis of the Earth's N biogeochemistry. In this work, we looked into the characteristics of the anammox hotspots' distribution across various types of ecosystems worldwide. Anammox hotspots are present at diverse oxic–anoxic interfaces in terrestrial systems, and they are most prevalent at the oxic–anoxic transition zone in aquatic ecosystems. Based on the discovery of an anammox hotspot capable of oxidizing ammonium anoxically into N2 without N2O by-product, we then designed an innovative concept and technical routes of nature-based anammox hotspot geoengineering for climate change, biodiversity loss, and efficient utilization of water resources. After 15 years of actual use, anammox hotspot geoengineering has proven to be effective in ensuring clean drinking water, regulating the climate, fostering plant and animal diversity, and enhancing long-term environmental quality. The sustainable biogeoengineering of anammox could be a workable natural remedy to resolve the conflicts between environmental pollution and food security connected to N management.