Spatial Distribution of Bioavailable Inorganic Nitrogen From Thawing Permafrost

Abstract

Arctic permafrost contains large amounts of nitrogen (N), which may be bioavailable upon permafrost thaw. Here, we have compiled inorganic N data from published studies on the active layer and permafrost layers combined with new data to quantify the spatial variability of bioavailable inorganic N in permafrost‐affected ecosystems across the Northern Hemisphere. Ammonium (NH4+) and nitrate (NO3−) are typically extracted from samples using different agents and strength. The results of an extraction experiment are here used to recalculate published concentrations on NH4+ and NO3− to a “water extractable fraction.” The results show that upper permafrost across all sites and samples contains significantly more NH4+ compared to the root zone and was significantly and positively correlated with an increasing water/ice content despite a surprisingly high variation within and between sites. Based on the average reported permafrost thaw rates (0.4–0.8 cm y−1) for wet and dry landscape types, the average release of inorganic N (NH4+ and NO3−) from wet tundra ecosystems was calculated to be 2.0 [1.13–2.61] kg N ha−1 decade−1 and 1.3 [0.78–1.81] kg N ha−1 decade−1 for dry ecosystems. This brings permafrost‐derived inorganic N on the same order of magnitude as biological nitrogen fixation in relatively dry tundra ecosystems but only marginally compared to nitrogen fixation in wet ecosystems. These landscape‐specific variations highlight the need for improving the understanding of N mobilization linked to permafrost thawing, but also that N transfer from well‐drained slopes to lower parts of the landscape can be important for the potential plant growth (greening) downslope from surrounding landscape types with faster permafrost thawing.

Elevation-dependent pattern of net CO2 uptake across China

“…Recent evidence suggests that the high-elevation environments of China have experienced an increasing trend of reactive N deposition, which is different from the decreasing temporal trend from cropland/city sites at lower elevations 24 . Elevation-dependent warming in high-elevation environments will also lead to a robust increase in mineralization 30 , adding nutrients for plant growth and thus increasing NEP. We therefore predict a general increase in NEP under the various climate scenarios, with a more robust change in NEP in high-elevation environments, whereas lower elevations will be affected by future limitations in the supply of nutrients, despite increases in both CO 2 concentrations and temperature 31 – 33 .…”

Microbial nitrogen and phosphorus co‐limitation across permafrost region

“…These cold areas have experienced a pronounced warming of ~2°C over the last 40 years (Ballinger et al, 2022) and are projected to release vast amounts of soil C (1.5–3.0 Pg C per decade), which could induce a strong positive feedback to global warming (Miner et al, 2022; Schuur et al, 2015). Vegetation productivity in cold regions is generally limited by low soil nutrient availabilities, and so climate warming is expected to enhance plant C assimilation by accelerating soil nutrients mineralization and releasing nutrients frozen in permafrost deposits (Hansen & Elberling, 2023; Keuper et al, 2017; Mao et al, 2020; Salmon et al, 2018). The increased plant C sequestration could partly counteract permafrost C losses and alleviate future climatic warming (Liu et al, 2022; Schuur et al, 2015).…”

Patterns and drivers of anaerobic nitrogen transformations in sediments of thermokarst lakes

“…This rapid warming is driving widespread permafrost thaw, resulting in previously ice‐locked organic matter being made available for microbial degradation: a process which will produce additional greenhouse gases, thus triggering a positive carbon‐climate feedback loop (Miner et al, 2022; Schuur et al, 2022; Turetsky et al, 2020). Importantly, large quantities of nitrogen (N) will be liberated by this permafrost thaw, which will then be able to affect vegetation productivity and gaseous N losses, exerting profound effects on the carbon‐climate feedback and also triggering a non‐carbon feedback to climate warming (Hansen & Elberling, 2023; Ramm, Liu, Ambus, et al, 2022; Voigt et al, 2020). Thermokarst lakes, formed by the collapse of ice‐rich permafrost, cover ~1.3 × 10 6 km 2 in the permafrost region and is one of the three major thermokarst landscapes (Olefeldt et al, 2016).…”

“…thaw, which will then be able to affect vegetation productivity and gaseous N losses, exerting profound effects on the carbon-climate feedback and also triggering a non-carbon feedback to climate warming (Hansen & Elberling, 2023;Ramm, Liu, Ambus, et al, 2022;Voigt et al, 2020). Thermokarst lakes, formed by the collapse of ice-rich permafrost, cover ~1.3 × 10 6 km 2 in the permafrost region and is one of the three major thermokarst landscapes (Olefeldt et al, 2016).…”