Abstract <p>Subarctic soils are a substantial reservoir of organic carbon (SOC) and are among the ecosystems being the most vulnerable to the ongoing global climate warming. The SOC distribution between particulate organic matter (POM) and mineral-associated organic matter (MAOM) pools in soils of the Siberian subarctic zone is considered. In most of soil horizons studied, the POM fraction contains more carbon than the MAOM fraction. The C-POM pool exceeds the C-MAOM pool in 1.1–6.2 times, thus indicating the predominance of unstabilized organic matter in subarctic soils. The mineralization efficiency of organic matter at 12°C averages 2.1% of total SOC and increases to 3.0% when a temperature rises to 22°C. Despite a comparable mineralization efficiency of these fractions, MAOM is characterized by the highest temperature sensitivity (Q₁₀ = 2.5–2.9). These findings emphasize that POM represents a primary source of CO₂ emissions from subarctic soils, whereas MAOM is the most vulnerable to temperature increase. Hence, the risk of enhanced soil carbon losses under the permafrost degradation is suggested.</p>