Abstract. The maintenance of the large soil organic carbon (SOC) stocks of the boreal forest under climate change is a matter of concern. In this study, major soil carbon pools and fluxes were assessed in twenty-two closed-canopy forests located along an elevation and latitudinal climatic gradient expanding 4 °C in mean annual temperature (MAT) for two important boreal conifer forest stand types: balsam fir (Abies balsamea) a fire avoider and black spruce (Picea mariana) a fire-tolerant species. SOC stocks were not influenced by climate or forest type. However, carbon fluxes, including aboveground litterfall rates as well as total soil respiration (R_s), heterotrophic (R_h) and autotrophic soil respiration (R_a) were linearly related to climate (cumulative degree days >5 °C). The sensitivity of SOM degradation to temperature, assessed by comparing Q₁₀ (rate of change for a T increase of 10 °C) of soil respiration and Rs₁₀ (soil respiration rates corrected to 10 °C) did not vary across the climate gradient, while the proportion of labile carbon and nitrogen showed higher values for balsam fir and for warmer sites. Balsam fir forests showed a greater litterfall rate, a better litter quality (lower C:N ratio) as well as a higher Rs₁₀ than black spruce ones, suggesting that their soils cycle a larger amount of C and N under a similar climate regime. Altogether, these results suggest that a warmer climate and balsam fir forest composition induce a more rapid SOC turnover. Contrary to common soil organic matter stabilization hypotheses, greater SOC cycling rates did not lead to higher total SOC stocks nor to the depletion of labile soil C and N. Positive effects of warming both on fluxes to and from the soil as well as a potential saturation of stabilised SOC could explain these results which apply to the context of this study: a cold and wet environment and a stable vegetation composition along the climate gradient.

中文翻译：

---

气候和森林组成对湿润北方地区土壤碳循环、土壤有机质稳定性和储量的影响

摘要。气候变化下北方森林大量土壤有机碳 (SOC) 储量的维持是一个值得关注的问题。在这项研究中，对位于海拔和纬度气候梯度扩大 4°C 的两种重要北方针叶林林分类型的 22 个封闭冠层森林中的主要土壤碳库和通量进行了评估：香脂冷杉( Abies balsamea ) 是一种防火树种，而黑云杉 ( Picea mariana ) 是一种耐火树种。SOC 储量不受气候或森林类型的影响。然而，碳通量，包括地上枯枝落叶率以及土壤总呼吸 (R _s )、异养 (R _h ) 和自养土壤呼吸 (R _a) 与气候呈线性相关（累积度数天数 > 5 °C）。SOM 降解对温度的敏感性，通过比较土壤呼吸的 Q ₁₀（T 增加 10 °C 的变化率）和 Rs ₁₀（校正至 10 °C 的土壤呼吸率）在气候梯度上没有变化，而在香脂冷杉和较温暖的地方，不稳定的碳和氮的比例显示出更高的值。香脂冷杉林表现出更高的凋落物率、更好的凋落物质量（更低的 C:N 比）以及更高的_10卢比与黑云杉相比，这表明它们的土壤在相似的气候条件下循环了更多的碳和氮。总之，这些结果表明温暖的气候和香脂冷杉森林的组成会导致更快速的 SOC 周转。与常见的土壤有机质稳定假设相反，更高的 SOC 循环速率不会导致更高的 SOC 总储量，也不会导致不稳定土壤 C 和 N 的消耗。变暖对进出土壤的通量以及潜在饱和度的积极影响稳定的 SOC 可以解释适用于本研究背景的这些结果：寒冷和潮湿的环境以及沿气候梯度的稳定植被组成。