Nitrogen Redox Controls on Greenhouse Gas Production in Yedoma Taliks

TL;DR

Arctic Yedoma permafrost thaw releases greenhouse gases like methane and nitrous oxide, with seasonal changes in microbial activity affecting emissions.

Contribution

This study reveals seasonal microbial dynamics in deep thawed Yedoma soils and their impact on greenhouse gas emissions.

Findings

Methanogenesis persists year-round in deep talik soils, with limited winter methanotrophy leading to elevated methane emissions.

Summer aerobic methanotrophy and nitrogen cycling reduce methane emissions but increase nitrous oxide production.

Longer, warmer summers may shift greenhouse gas emissions from methane to nitrous oxide in Yedoma uplands.

Abstract

Large carbon and nitrogen pools are disproportionately concentrated in the icy, Pleistocene‐aged silt deposits of Arctic Yedoma permafrost. Upon thaw, these undergo microbial mineralization, releasing greenhouse gases (GHGs) including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Here, we present combined geochemical data with microbial function and community dynamics from deep (7‐m) talik soil boreholes in water‐unsaturated yedoma upland in interior Alaska. Our results reveal significant in situ seasonal shifts in microbial function, community composition, and diversity throughout the talik. Methanogenesis persisted in the deep talik year‐round. Winter methanotrophy was negligible within and above the methanogenic zone, leading to elevated CH4 production and emission to the atmosphere. This is likely due to reduced microbial methanotrophic activity associated with lower temperatures and nitrogen availability. During summer, strong aerobic methanotrophy near the soil surface reduced CH4 emissions. Nitrate/nitrite‐mediated anaerobic oxidation of methane (AOM) by both archaea (ANME‐2d clade) and bacteria (NC10 phylum) occurred at and above the anoxic methanogenic zone, further offsetting CH4 production. In contrast to CH4 production potentials, which were higher in surface soils in winter compared to summer, we observed higher N2O production potentials in summer compared to winter. Nitrous oxide concentrations peaked at 10 cm (7.2 μM) and 105 cm (6.7 μM) and were associated with denitrification; nitrogen‐mediated AOM by Methanoperedens (ANME2d). In the summer only and within the top 1 m of soil, high expression of nitrogen‐related genes (narG, norB, amoA, Annamox, and Feammox) indicated active redox dynamics, potentially providing nitrogen species for AOM. The potential N2O production in summer may imply higher net GHG emissions from yedoma uplands as climate change leads to longer summers and warmer soils in the future.

Arctic Yedoma permafrost holds large carbon and nitrogen pools that, when thawed, undergo microbially mediated processes that release greenhouse gases like methane and nitrous oxide. We analyzed seasonal shifts in microbial community dynamics and geochemistry in deep thawed soils (talik) and found year‐round methane production, with limited winter methane consumption and corresponding elevated methane emissions to the atmosphere. In summer, increased methane oxidation and active nitrogen cycling coincided with higher nitrous oxide production. These findings suggest that longer, warmer summers may shift greenhouse gas emissions from predominantly winter methane to increased summer nitrous oxide release in Yedoma uplands.

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