Nitrogen Addition Regulates the Temperature Sensitivity of Soil Carbon Release via Microbial Properties

The temperature sensitivity (Q₁₀) of soil carbon (C) release is a key parameter for evaluating soil C stability under climate warming, with particular importance in high-latitude regions that are highly vulnerable to rising temperatures. Nevertheless, the mechanisms by which nitrogen (N) addition modulates the temperature sensitivity of soil C release remain insufficiently understood. Here, we collected soils from a long-term N addition experiment in a high-latitude boreal forest and conducted controlled incubations to assess how N addition influences soil CO₂ release and its temperature sensitivity. We found that N addition significantly suppressed soil CO₂ release across all incubation temperatures (5°C, 15°C, and 25°C), yet its effects on Q₁₀ were nonlinear. Specifically, N addition enhanced Q₁₀ between 5°C and 15°C but suppressed Q₁₀ between 15°C and 25°C. Both CO₂ release and Q₁₀ were strongly associated with bacterial and fungal diversity and biomass, as well as with the activities of key C- and N-cycling enzymes (e.g., β-glucosidase, cellobiohydrolase, and N-acetyl-glucosaminidase). However, the effects of N addition on CO₂ release and Q₁₀ were primarily mediated through both direct and indirect influences on microbial properties. Together, these findings demonstrate that N addition regulates soil CO₂ release and Q₁₀ mainly through microbial pathways, underscoring the pivotal role of microbial processes in determining high-latitude carbon dynamics and their feedbacks to climate change.