Microbiogeochemical Traits to Identify Nitrogen Hotspots in Permafrost Regions

Abstract

Permafrost-affected tundra soils are large carbon (C) and nitrogen (N) reservoirs. However, N is largely bound in soil organic matter (SOM), and ecosystems generally have low N availability. Therefore, microbial induced N-cycling processes and N losses were considered negligible. Recent studies show that microbial N processing rates, inorganic N availability, and lateral N losses from thawing permafrost increase when vegetation cover is disturbed, resulting in reduced N uptake or increased N input from thawing permafrost. In this review, we describe currently known N hotspots, particularly bare patches in permafrost peatland or permafrost soils affected by thermokarst, and their microbiogeochemical characteristics, and present evidence for previously unrecorded N hotspots in the tundra. We summarize the current understanding of microbial N cycling processes that promote the release of the potent greenhouse gas (GHG) nitrous oxide (N2O) and the translocation of inorganic N from terrestrial into aquatic ecosystems. We suggest that certain soil characteristics and microbial traits can be used as indicators of N availability and N losses. Identifying N hotspots in permafrost soils is key to assessing the potential for N release from permafrost-affected soils under global warming, as well as the impact of increased N availability on emissions of carbon-containing GHGs.

Yedoma Permafrost Releases Organic Matter with Lesser Affinity for Cu2+ and Ni2+ as Compared to Peat from the Non-Permafrost Area: Risk of Rising Toxicity of Potentially Toxic Elements in the Arctic Ocean

“…The C/N ratio of 13.9 is significantly lower for DY2 HA, while PE and DY1 have C/N ratios of 17.1 and 17.2, respectively. The lower values of the C/N ratio and the higher content of nitrogen in the Yedoma permafrost HA sample may be connected with lower rates of microbial nitrogen consumption [ 62 ] or the changes in the vegetation during the formation of permafrost layers, as sphagnum spp. which are presently common for bogs have a higher C/N ratio than flora which was common in fens [ 63 ].…”

Nitrous Oxide Fluxes in Permafrost Peatlands Remain Negligible After Wildfire and Thermokarst Disturbance

“…We expected wildfire disturbance to lead to increased N 2 O emissions linked to enhanced availability of NH 4 + and NO 3 − , possibly caused by (a) reduced plant demand due to a lack of vegetation as observed from bare peat surfaces on palsa and peat plateau surfaces in Eurasia (Fiencke et al., 2022; Marushchak et al., 2011; Repo et al., 2009; Voigt et al., 2017), (b) mineralization of organic matter during combustion (Walker et al., 2019, 2020), and (c) increased soil mineralization in the years after wildfire due to warmer soils and a deeper active layer (Gibson et al., 2018), potentially resulting in a flush of higher nutrient supply, specifically inorganic N, from recently thawed, deeper soil layers (Ackley et al., 2021; Keuper et al., 2012; Ramm et al., 2022; Salmon et al., 2018). In addition to inorganic N, the availability of PO 4 3− supply can fuel nitrification and enhance N 2 O production (Liimatainen et al., 2018) by stimulating microbial activity (F. Wang et al., 2014).…”

“…However, our results showed the opposite as overall N 2 O uptake, and thus N 2 O consumption increased with surface soil temperatures during the peak growing season. Emissions of N 2 O are subject to high temporal (hot moments) and spatial (hot spots) variability (Fiencke et al., 2022; Marushchak et al., 2011; McClain et al., 2003). Although we did not observe high N 2 O emissions at the soil surface of our study sites, we measured increased N 2 O soil gas concentrations at depth in two out of 15 Peat Plateau plots, indicating active N 2 O production.…”

Carbon‐cycling microorganisms in permafrost and their responses to a warming climate: A review

“…Recent advances have underlined the importance of nitrogen in modulating microbial carbon turnover 36–38 . Nitrogen availability is often limited in permafrost soils, and varies with ecosystem, soil layer, or season 36,39 .…”

“…Recent advances have underlined the importance of nitrogen in modulating microbial carbon turnover. [36][37][38] Nitrogen availability is often limited in permafrost soils, and varies with ecosystem, soil layer, or season. 36,39 Meanwhile, long-term freezing in permafrost has resulted in deficient microbial nitrogen cycling, hindering biogeochemical processes.…”