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 (NH 4 + ) and nitrate (NO 3 − ) are typically extracted from samples using different agents and strength. The results of an extraction experiment are here used to recalculate published concentrations on NH 4 + and NO 3 − to a “water extractable fraction.” The results show that upper permafrost across all sites and samples contains significantly more NH 4 + 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 (NH 4 + and NO 3 − ) 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.