Carbon Stocks and Fluxes from a Mixed Dark Conifers–Aspen Forest in the Middle Taiga of Western Siberia, Russia

Forests are undergoing significant transformation due to anthropogenic activity and climate change, which is reflected in the structure of forest stands. Mixed forests are becoming the most common community type, yet data on their total C stocks and cycling (including the coupled nitrogen (N) cycle) in the boreal zone of Russia remain scarce. We investigated above- and below-ground C and N stocks using forest taxation, soil monolith, and soil pit sampling, as well as growing season carbon dioxide fluxes using automated chamber system, in a representative middle-taiga mixed dark conifers–aspen forest at the Mukhrino field station (Western Siberia, Russia) in 2024. Our results show that this boreal mixed forest stores 21.6 ± 0.9 kg C/m2 and 593 ± 24 g N/m2. While 57% of the total C stock was contained in the tree biomass, only 36% of the total organic carbon was found in the soil, including the forest floor. In contrast, 91% of the total N was stored in the soil, specifically within the mineral horizons (84%). Total understory respiration (combined respiration of soil, tree roots, and understory vegetation) from June to September was 597 g C/m2, with soil temperature acting as the dominant control during the growing season. The relatively low soil C stock and its contribution to the total ecosystem C pool could be explained by a relatively high litter decomposition rate, the limited ability of quartz-dominated mineral particles to adsorb organic matter and protect it from decomposition, and low nitrogen availability. This explanation is supported by the relatively high values of understory respiration, as well as high microbial biomass carbon and basal respiration in the forest floor and soil compared to other middle taiga forests.