Figure Schematic processes of nitrogen cycle driven by microorganisms (Francis CA, Beman JM, Kuypers MMM. New processes and players in the nitrogen cycle: the microbial ecology of anaerobic and archaeal ammonia oxidation. ISME Journal, 2007, 1: 19‒27.; Canfield DE, Glazer AN, Falkowski PG. The evolution and future of earth’s nitrogen cycle. Science 2010, 330: 192‒196.; Coskun D, Britto DT, Shi WM, Kronzucker HJ. 2017. How plant root exudates shape the nitrogen cycle. Trends in Plant Science 22: 661‒673.; Kuypers MMM, Marchant HK, Kartal B. 2018. The microbial nitrogen‒cycling network. Nature Reviews Microbiology 16, 263‒276).

注：Oxic，常氧环境；Suboxic，次氧化环境；N₂ fixation，固氮作用；Nitrification，硝化作用；Ammonia oxidation，氨氧化作用；Nitrite oxidation，亚硝化作用；Denitrification，反硝化作用；Anammox，厌氧氨氧化作用；DNRA (Dissimilatory nitrate reduction to ammonium)，硝酸盐异化还原为氨；nifH，固氮酶(Nitrogenase)铁蛋白(催化N₂→NH₄⁺)基因；amoA，氨单加氧酶(Ammonia monooxygenase) (催化NH₄⁺→NO₂^‒)基因；hao，羟胺氧化酶(Hydroxylamine oxidoreductase) (催化NH₂⁺OH→NO₂^‒)基因；nxrA，亚硝酸盐氧化还原酶(Nitrite oxidoreductase) (催化NO₂^‒→NO₃^‒)基因；narG，膜靠硝酸盐还原酶(Membrane‒bound Nitrate Reductase) (催化NO₃^‒→NO₂^‒)基因；napA，可溶性细胞质硝酸盐还原酶(Periplasmic‒bound nitrate reductase) (催化NO₃^‒→NO₂^‒)基因；nirK，含铜离子的亚硝酸盐还原酶(Copper‒containing nitrite reductase) (催化NO₂^‒→NO)基因；nirS，含细胞色素cd1亚硝酸盐还原酶(Cytochrome cd1‒containing nitrite reductase) (催化NO₂^‒→NO)基因；norB，NO还原酶(Nitric oxide reductase) (催化NO→N₂O)基因；nosZ，N₂O还原酶(Nitrous oxide reductase) (催化N₂O→N₂)基因；nrfA，异化氮还原氨(Dissimilatory nitrate reductase) (催化NO₂^‒→NH₄⁺)基因；hzo，厌氧氨氧化酶(Anaerobic ammonium oxidase) (催化NH₄⁺→N₂)基因。