In recent years, wildfire frequency and severity has increased in the Arctic tundra regions due to climate change. Pyrogenic organic matter (PyOM) is a product of incomplete combustion of biomass containing nutrients such as nitrogen (N), and is expected to affect ecosystem N cycling during a post-fire recovery period. We investigated effects of fire on soil biogeochemical cycles with a focus on pyrogenic N turnover over two subsequent growing seasons, combined with and without summer warming, in an Arctic heath tundra, West Greenland. The summer warming was achieved by deployment of open top chambers (OTCs). We simulated an in situ tundra fire by removing vegetation and litter, and scorching/heating soil surface followed by the addition of ¹⁵N-labelled PyOM (derived from aboveground biomass and litter) to the soil surface in plots with and without summer warming. A darker surface after the simulated fire resulted in an increase of 1.3 °C in soil temperature at 5-cm depth over the growing seasons. The fire also caused a nine-fold increase in soil NH₄⁺-N and three-fold increase in soil NO₃⁻-N concentrations at 7-cm depth after two years. Tracing the fate of ¹⁵N-labelled PyOM, 21 days after its application, showed low ¹⁵N recovery in microbial biomass (0.4%) and total dissolved N (TDN) pools (0.01%). Microbial and root ¹⁵N recovery increased two-fold and 15-fold after one year, respectively, and TDN ¹⁵N recovery increased two-fold after two years, suggesting that relatively recalcitrant N of PyOM can be partly transformed into plant-available forms over time. Root and TDN ¹⁵N recovery was also significantly higher after two years of summer warming than under ambient temperature conditions, suggesting that summer warming can enhance availability of PyOM-N for recovering plants after the fire. Hence, we conclude that fire-induced PyOM can act as an N source for plant recovery in this Arctic tundra ecosystem for years after the fire, and this N source will become increasingly important in a future warmer climate.

近年来，由于气候变化，北极苔原地区的野火频率和严重程度有所增加。热解有机物 (PyOM) 是含有氮 (N) 等营养物质的生物质不完全燃烧的产物，预计会在火灾后恢复期间影响生态系统 N 循环。我们研究了火对土壤生物地球化学循环的影响，重点是在西格陵兰岛的北极荒地苔原中，在随后的两个生长季节，结合和不结合夏季变暖，火原氮的转换。夏季变暖是通过部署开顶室 (OTC) 实现的。我们通过去除植被和枯枝落叶、烧焦/加热土壤表面，然后添加¹⁵在有和没有夏季变暖的情况下，N 标记的 PyOM（来自地上生物量和枯枝落叶）到土壤表面。模拟火灾后较暗的表面导致生长季节 5 厘米深度的土壤温度升高 1.3°C。两年后，火灾还导致 7 厘米深度的土壤 NH ₄ ⁺ -N 浓度增加了 9 倍，土壤 NO ₃ ^{- -N 浓度增加了 3 倍。}在应用 21 天后追踪¹⁵ N 标记的 PyOM的命运，显示微生物生物量 (0.4%) 和总溶解 N (TDN) 池 (0.01%) 中的^{15 N 回收率较低。}一年后微生物和根^{15 N 回收率分别增加了两倍和 15 倍，TDN 15}两年后 N 回收率增加了两倍，这表明 PyOM 中相对顽固的 N 可以随着时间的推移部分转化为植物可利用的形式。经过两年的夏季变暖后，根和 TDN ^{15 N 的回收率也显着高于环境温度条件下，这表明夏季变暖可以提高 PyOM-N 在火灾后恢复植物的可用性。}因此，我们得出的结论是，火灾引起的 PyOM 可以作为火灾后多年在这个北极苔原生态系统中植物恢复的 N 源，并且这种 N 源在未来变暖的气候中将变得越来越重要。