With an rise in temperature in the circumpolar region, an increase in the frequency of fires can be expected. We studied the effects of fire in larch (Lárix sibírica Lebed.) forests on the organic matter composition of topsoils of Leptosols in the Subpolar Ural Mountains (northern taiga, Komi Republic, Russian Federation). We compared topsoils before the fire (BF), during the low-intensity surface fire (DF), one (1AF) and two years (2AF) after the fire. The low intensity surface fire burnt only the upper part of the organic horizon, leading to the formation of a thin pyrogenic horizon. The soil alteration included alkalization of the solution by three pH units, threefold increase in the content of exchangeable forms of cations, a nine times increase in the specific surface area of the solid phase, increase in total carbon and nitrogen contents, and a five-fold increase in the aromaticity of the organic matter. The latter is mirrored by a strong increase in benzene polycarboxylic acids (BPCAs) as marker for pyrogenic carbon (PyC), representing 82 to 97 mg BPCA C g^-1C. Two years after the fire, arrival of fresh litter, intensified water regime and soil acidification led to a decline of the surface area of organic horizons. Thus, it was revealed that two years after a low-intensity fire, the soils differed from the initial ones in a total carbon and nitrogen contents, the organic matter aromaticity and the BPCA contents. The content of aromatic fragments in pyrogenic horizon evaluated according ¹³C NMR spectroscopy decreased after two years after fire, but at the same time, the PyC concentration, estimated on the carbon of BPCAs, remains stable. This indicates that periodically repeating low-intensity fires in boreal northern forests can contribute to the accumulation of stable forms of PyC in soils.

随着极地地区温度的升高，可以预期火灾频率会增加。我们研究了落叶松 (Lárix sibírica Lebed.) 森林中的火灾对亚极地乌拉尔山脉（俄罗斯联邦科米共和国北部针叶林）Leptosols 表土有机质组成的影响。我们比较了火灾前 (BF)、低强度地表火灾 (DF)、火灾后一年 (1AF) 和两年 (2AF) 的表土。低强度的地表火灾仅烧毁了有机层的上部，导致形成薄的热成层。土壤改变包括溶液碱化三个 pH 单位，可交换形式的阳离子含量增加三倍，固相比表面积增加九倍，总碳和氮含量增加，并且有机物的芳香度增加了五倍。后者反映为苯多羧酸 (BPCA) 作为热解碳 (PyC) 的标志物的强烈增加，代表 82 至 97 mg BPCA C g^-1 C. 火灾发生两年后，新鲜凋落物的到来、水势加剧和土壤酸化导致有机层表面积下降。因此，揭示了低强度火灾两年后，土壤的总碳和氮含量、有机质芳香性和 BPCA 含量与初始土壤不同。燃烧两年后，根据¹³ C NMR 光谱评估的热解层中芳烃碎片的含量 下降，但与此同时，根据 BPCA 的碳估计的 PyC 浓度保持稳定。这表明北方北方森林中周期性重复的低强度火灾可能有助于土壤中稳定形式的 PyC 的积累。