Rapid Permafrost Thaw Removes Nitrogen Limitation and Rises the Potential for N 2 O Emissions

• Published in: Nitrogen
• Main Authors: Rica Wegner, Claudia Fiencke, Christian Knoblauch, Lewis Sauerland, Christian Beer
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: ammonification; nitrification; N 2 O; denitrification; thermoerosion; retrogressive thaw slumps; Ecology; QH540-549.5; Ice; lena river; permafrost; Siberia
• Online Access: https://doi.org/10.3390/nitrogen3040040; https://doaj.org/article/632b4f48752b4b4ea4fce78934b52aab

Ice–rich Pleistocene permafrost deposits (Yedoma) store large amounts of nitrogen (N) and are susceptible to rapid thaw. In this study, we assess whether eroding Yedoma deposits are potential sources of N and gaseous carbon (C) losses. Therefore, we determined aerobic net ammonification and nitrification, as well as anaerobic production of nitrous oxide (N 2 O), carbon dioxide (CO 2 ), and methane (CH 4 ) in laboratory incubations. Samples were collected from non-vegetated and revegetated slump floor (SF) and thaw mound (TM) soils of a retrogressive thaw slump in the Lena River Delta of Eastern Siberia. We found high nitrate concentrations (up to 110 µg N (g DW) −1 ) within the growing season, a faster transformation of organic N to nitrate, and high N 2 O production (up to 217 ng N 2 O-N (g DW) −1 day −1 ) in revegetated thaw mounds. The slump floor was low in nitrate and did not produce N 2 O under anaerobic conditions, but produced the most CO 2 (up to 7 µg CO 2 -C (g DW) −1 day −1 ) and CH 4 (up to 65 ng CH 4 -C (g DW) −1 day −1 ). Nitrate additions showed that denitrification was substrate limited in the slump floor. Nitrate limitation was rather caused by field conditions (moisture, pH) than by microbial functional limitation since nitrification rates were positive under laboratory conditions. Our results emphasize the relevance of considering landscape processes, geomorphology, and soil origin in order to identify hotspots of high N availability, as well as C and N losses. High N availability is likely to have an impact on carbon cycling, but to what extent needs further investigation.