Nitrogen Redox Controls on Greenhouse Gas Production in Yedoma Taliks

Area of Science:

• Environmental Microbiology
• Geochemistry
• Permafrost Science

Background:

• Arctic Yedoma permafrost stores large carbon and nitrogen pools, vulnerable to thaw.
• Microbial mineralization of thawing permafrost releases greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).

Purpose of the Study:

• To investigate in situ seasonal microbial function, community dynamics, and GHG production in Alaskan Yedoma permafrost talik.
• To quantify methane (CH4) and nitrous oxide (N2O) cycling under varying temperature and nitrogen availability.

Main Methods:

• Analysis of geochemical data from deep (7-m) talik soil boreholes.
• Assessment of microbial community composition, diversity, and function.
• Measurement of in situ seasonal shifts in microbial activity and gene expression.

Main Results:

• Year-round methanogenesis occurred in the deep talik; winter methanotrophy was negligible, increasing CH4 emissions.
• Summer aerobic methanotrophy near the surface reduced CH4 emissions, while anaerobic oxidation of methane (AOM) by archaea and bacteria occurred.
• Higher N2O production potentials were observed in summer, linked to denitrification and nitrogen-mediated AOM, with peak concentrations at 10 cm and 105 cm depths.

Conclusions:

• Seasonal shifts in microbial processes significantly control GHG fluxes from Yedoma permafrost.
• Reduced winter methane oxidation enhances net CH4 release, while summer denitrification and AOM contribute to N2O production.
• Future climate warming may increase net GHG emissions from Yedoma uplands due to longer, warmer summers.