The changes in the total soil carbon storage and the pools of labile and potentially mineralizable organic matter in Entic Folic Podzols of the Khibiny Mountains (Murmansk region, NW Russia) caused by wildfires of high and moderate intensity and during the post-fire succession are discussed. Although a moderate-intensity wildfire has no statistically significant impact on the total soil carbon pool, it triggers the active erosion processes leading to the carbon losses comparable to the direct pyrogenic carbon losses in a high-intensity fire. In the postfire soil restoration, the type of organic carbon accumulation changes: the surface carbon accumulation in the form of peat is characteristic of the control site, while up to half of soil carbon is accumulated in the mineral horizons at late stages of the postpyrogenic succession. A high-intensity fire leads to almost complete destruction of labile, microbial, and potentially mineralizable carbon pools in both the organic (pyrogenic) and mineral horizons. A moderate-intensity fire does not cause any statistically significant changes in these pools as compared to the control. The restoration dynamics of the labile and potentially mineralizable pools of organic matter in the pyrogenic horizons of soil differ: the trend of a steady increase in the pools of labile and microbial carbon is observed for three years after the fire and later, while the pool of potentially mineralizable carbon reaches its maximum three years after the fire and then becomes stabilized at this level.

The dynamics of the content and microbiological transformation of carbon and nitrogen compounds in the surface horizons of mountain tundra soils are considered in the postpyrogenic succession. The...

Agriculture is the main contributor to nitrous oxide (N₂O) emission, but the emission intensity can be controlled by various factors, in particular, the activity of earthworms, one of the most common groups of soil invertebrates. We conducted an incubation experiment to evaluate N₂O emission in earthworm soil samples compared to non-earthworm ones with applications of high (200 kg ha⁻¹) and low (50 kg ha⁻¹) mineral N fertilizer doses. We assessed the cumulative N₂O emission, the dynamics of the soil dissolved organic carbon, and the soil microbial carbon and nitrogen content, as well as the number of nirK and nirS gene copies in bulk soil samples and in isolates from the earthworms’ gut. Our study showed a significant role of the earthworm activity in changing the intensity of N₂O emission after the application of mineral N fertilizers. The main factor leading to an increase in nitrous oxide emission in the presence of earthworms is the stimulation of free-living soil denitrifiers by the organic matter of the earthworms’ excretions, as well as the thorough mixing of plant residues and soil. Contrary to our expectations, earthworms did not increase the representation of nitrite reductase genes in soil, although the earthworm’s gut can be considered as a refugium for denitrifiers. Our results indicate a possible risk of increased N₂O emission from arable temperate soils with an increase in earthworm populations as the climate warms, even if application rates of mineral fertilizers are reduced.