Distributive features of soil carbon and nutrients in permafrost regions affected by forest fires in northern Da Xing'anling (Hinggan) Mountains, NE China

In permafrost regions, forest fires actively affect physical and chemical properties of soils. Many studies have been conducted on the effects of forest fires on physical and chemical properties of topsoil, while the research on the fire-induced changes in carbon and other nutrients of soils has received much less attention, particularly that of soils in the active layer and near-surface permafrost. Here, using soil samples from two representative areas (Mangui and Alongshan), we investigated the effects of fires on soil nutrients of larch forest soils in the discontinuous permafrost zone in the northern Da Xing'anling (Hinggan) Mountains, Northeast China. The results showed that soil pH increased with fire severity due to the burning of soil organic matter by more severe fires and leaching of base elements in the residual ash into the soil, and; forest fires resulted in a weakly acidic post-fire soil environment. Soil total organic carbon, total nitrogen, and total phosphorus declined with increasing fire severity. A severe burn led to a substantial reduction of soil carbon and nitrogen, which were not recovered seven years after fire. However, there was no substantial change in the C/N ratio. For the two chosen areas, soil C/N ratios decreased with depth. In the first post-fire year, total potassium content increased and were similar at the sites affected by fires of different severity in the area burned seven years ago. There was no significant change in available phosphorus and available potassium. These changes were notable in the active layer and/or organic layers, but not so in the near-surface permafrost layer. Our results suggest that, in permafrost regions, forest fires have important effects on the distribution of soil carbon and other nutrients. This study on the feedback mechanisms between forest fires and nutrients in discontinuous permafrost regions in the northern Da Xing'anling Mountains is of importance for understanding the boreal carbon pool and cycling.