biostudies-literatureUnknown14Rempfert KRNitrogen (N) is an essential element for life. N compounds such as ammonium ( NH4+ ) may act as electron donors, while nitrate ( NO3- ) and nitrite ( NO2- ) may serve as electron acceptors to support energy metabolism. However, little is known regarding the availability and forms of N in subsurface ecosystems, particularly in serpentinite-hosted settings where hydrogen (H₂) generated through water-rock reactions promotes habitable conditions for microbial life. Here, we analyzed N and oxygen (O) isotope composition to investigate the source, abundance, and cycling of N species within the Samail Ophiolite of Oman. The dominant dissolved N species was dependent on the fluid type, with Mg²⁺- HCO3- type fluids comprised mostly of NO3- , and Ca²⁺-OH^- Frontiers in microbiology1139633https://www.ebi.ac.uk/biostudies/studies/S-EPMC10160414biostudies-literatureSubsurface biogeochemical cycling of nitrogen in the actively serpentinizing Samail Ophiolite, Oman.PMC10160414Asamoto CKNothaft DBRempfert KRTempleton ASEvans RDMatter JMKopf SHKraus EASpear JRfalseSubsurface biogeochemical cycling of nitrogen in the actively serpentinizing Samail Ophiolite, Oman.Nitrogen (N) is an essential element for life. N compounds such as ammonium ( NH4+ ) may act as electron donors, while nitrate ( NO3- ) and nitrite ( NO2- ) may serve as electron acceptors to support energy metabolism. However, little is known regarding the availability and forms of N in subsurface ecosystems, particularly in serpentinite-hosted settings where hydrogen (H₂) generated through water-rock reactions promotes habitable conditions for microbial life. Here, we analyzed N and oxygen (O) isotope composition to investigate the source, abundance, and cycling of N species within the Samail Ophiolite of Oman. The dominant dissolved N species was dependent on the fluid type, with Mg²⁺- HCO3- type fluids comprised mostly of NO3- , and Ca²⁺-OH^- 2023-01-01T00:00:00Z20232025-04-22T05:13:18.715Z2025-04-05T21:14:08.456ZS-EPMC101604143715273110.3389/fmicb.2023.1139633