Nitrogen(N) is a key nutrient controlling ecosystem structure and function. Microbial denitrification and anammox can convert inorganic N, such as nitrate, nitrite, and ammonium, to gaseous N, resulting in significant ecosystem N losses. Despite attempts to understand the relative contributions of denitrification and anammox to N loss across diverse terrestrial and aquatic ecosystems globally, this knowledge remains elusive. This gap limits our ability to forecast how human activities are impacting the global N cycle.

A recent study conducted by researchers from Wuhan Botanical Garden and the Instituto de Recursos Naturales y Agrobiología de Sevilla in Spain constructed a global dataset on the relative contributions of denitrification and anammox to global ecosystem N loss by reviewing the published studies over the past decades.

This study is the first to assess the relative importance of denitrification and anammox in N loss from soils, sediments, and water bodies on a global scale, highlighting that denitrification governs global microbial N losses and that anammox is more prominent in aquatic ecosystems than that in terrestrial ecosystems. The study also identifies the key geographic, climatic, and environmental factors that control their relative contributions.

Machine learning models were also used to predict and map the relative contributions of denitrification and anammox processes to N loss in terrestrial surface soils globally. The results show that the regions with the most significant contribution of denitrification to N loss are mainly concentrated in the North American Great Plains, Eastern European Plains, Brazilian Plateau, and Congo Basin. Finally, the annual contribution of denitrification and anammox processes to N loss in different ecosystems was also estimated. 

The study fills the knowledge gap on microbial N loss in global ecosystems, and the results have important implications for reducing N loss in agricultural and forestry ecosystems and enhancing N removal in wetland water columns.

Results were published in Advanced Science, titled "Global Relative Importance of Denitrification and Anammox in Microbial Nitrogen Loss Across Terrestrial and Aquatic Ecosystems". HE Gang and DENG Danli are the first authors, and Prof. LIU Wenzhi and MANUEL Delgado-Baquerizo are the corresponding authors. This study was supported by the National Natural Science Foundation of China and the Hubei Provincial Natural Science Foundation of China.

Annual contribution of denitrification and anammox to nitrogen losses in different ecosystems (Image by HE Gang)