Abstract
Permafrost-affected landscape soils are rich in organic matter and contain a high fraction of organic nitrogen, but much of this organic matter remains inaccessible due to nitrogen limitation. Microbial nitrification is a key process in the nitrogen cycle, controlling the availability of dissolved inorganic nitrogen (DIN) such as ammonium and nitrate. In this study, we investigate the microbial diversity of canonical nitrifiers and their potential nitrifying activity in the active layer of different Arctic cryosols in the Lena River Delta in North-East Siberia. These cryosols are located on Samoylov Island, which has two geomorphological landscapes with mineral soils in the modern floodplain and organic-rich soils in the low-centered polygonal tundra of the Holocene river terrace. Microcosm incubations show that the highest potential ammonia oxidation rates are found in low organic soils, and the rates depend on organic matter content and quality, vegetation cover, and water content. As shown by 16S rRNA amplicon sequencing, nitrifiers represented 0.6% to 6.2% of the total microbial community. More than 50% of the nitrifiers belonged to the genus Nitrosospira. Based on PCR amoA analysis, ammonia-oxidizing bacteria (AOB) were found in nearly all soil types, whereas ammonia-oxidizing archaea (AOA) were only detected in low-organic soils. In cultivation-based approaches, mainly Nitrosospira-like AOB were enriched and characterized as psychrotolerant, with temperature optima slightly above 20 °C. This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms (bacteria and archaea) in permafrost-affected landscapes of Siberia with cold-adapted AOB, especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols.
Highlights
Tundra landscapes and their cold soils play an important role in the global carbon (C) and nitrogen (N) cycle
This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms in permafrost-affected landscapes of Siberia with cold-adapted ammonia-oxidizing bacteria (AOB), especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols
In all samples of the sandy soils (Psammorthel and Psammentic Aquorthel according to soil survey staff [54]) of the modern floodplain and the dry river terrace, potential ammonia-oxidizing activities were measured between 100 and 600 ng N g–1 dw h–1 in the absence of antibiotics
Summary
Tundra landscapes and their cold soils (cryosols) play an important role in the global carbon (C) and nitrogen (N) cycle. Since topography in arctic terrestrial ecosystems influences these environmental control factors, the N-cycle and N-availability in permafrost-affected soils is driven by arctic microscale and topographic variations [6,13,14]. In these N-limited ecosystems, the N-availability is an important key driver of the N- as well as C-cycle and the balance between primary production and soil organic matter composition. It influences the formation of the climate relevant gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which will increase because of the warming of subarctic tundra [12,15,16,17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
