Production of N2 through Anaerobic Ammonium Oxidation Coupled to Nitrate Reduction in Marine Sediments
AUTOR(ES)
Thamdrup, Bo
FONTE
American Society for Microbiology
RESUMO
In the global nitrogen cycle, bacterial denitrification is recognized as the only quantitatively important process that converts fixed nitrogen to atmospheric nitrogen gas, N2, thereby influencing many aspects of ecosystem function and global biogeochemistry. However, we have found that a process novel to the marine nitrogen cycle, anaerobic oxidation of ammonium coupled to nitrate reduction, contributes substantially to N2 production in marine sediments. Incubations with 15N-labeled nitrate or ammonium demonstrated that during this process, N2 is formed through one-to-one pairing of nitrogen from nitrate and ammonium, which clearly separates the process from denitrification. Nitrite, which accumulated transiently, was likely the oxidant for ammonium, and the process is thus similar to the anammox process known from wastewater bioreactors. Anaerobic ammonium oxidation accounted for 24 and 67% of the total N2 production at two typical continental shelf sites, whereas it was detectable but insignificant relative to denitrification in a eutrophic coastal bay. However, rates of anaerobic ammonium oxidation were higher in the coastal sediment than at the deepest site and the variability in the relative contribution to N2 production between sites was related to large differences in rates of denitrification. Thus, the relative importance of anaerobic ammonium oxidation and denitrification in N2 production appears to be regulated by the availability of their reduced substrates. By shunting nitrogen directly from ammonium to N2, anaerobic ammonium oxidation promotes the removal of fixed nitrogen in the oceans. The process can explain ammonium deficiencies in anoxic waters and sediments, and it may contribute significantly to oceanic nitrogen budgets.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=123779Documentos Relacionados
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