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 22 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 a warmer climate or by forest type. However, carbon fluxes, including aboveground litterfall rates, as well as total soil respiration (R_s) and heterotrophic (R_h) and autotrophic soil respiration (R_a), were linearly related to temperature (cumulative degree days >5 ^∘C). The sensitivity of soil organic matter (SOM) degradation to temperature, assessed by comparing Q₁₀ (rate of change for a T increase of 10 ^∘C) of soil respiration and R_s10 (soil respiration rates corrected to 10 ^∘C), did not vary along the temperature gradient, while the proportion of bioreactive 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) and a higher R_s10 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 a balsam fir forest composition induce a more rapid SOC turnover. Contrary to common soil organic matter stabilisation hypotheses, greater litter input rates did not lead to higher total SOC stocks, and a warmer climate did not lead to the depletion of bioreactive 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 temperature gradient. While the entire study area is subject to a humid climate, a negative relationship was found between aridity and SOM stocks in the upper mineral soil layer for black spruce forests, suggesting that water balance is more critical than temperature to maintain SOM stocks.

中文翻译：

---

气候变暖和森林成分对北方潮湿地区土壤碳循环、土壤有机质稳定性和储量的影响

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，评估了 22 个封闭冠层森林中的主要土壤碳库和通量，这些森林位于海拔和纬度气候梯度扩大 4  ^∘ C 的年平均温度 (MAT) 中，两种重要的北方针叶林林分类型：香脂冷杉 ( Abies ) balsamea )，一种防火植物，和黑云杉 ( Picea mariana )，一种耐火树种。SOC 储量不受气候变暖或森林类型的影响。然而，碳通量，包括地上凋落物率，以及土壤总呼吸 ( R _s ) 和异养 ( R _h) 和自养土壤呼吸 ( R _a ) 与温度呈线性相关（累积度数天数> 5  ^∘ C）。通过比较土壤呼吸的Q ₁₀（T增加 10  ^∘ C 的变化率）和R _s10（校正为 10  ^∘ C 的土壤呼吸速率）评估土壤有机质 (SOM) 降解对温度的敏感性 ，没有随温度梯度变化，而生物活性碳和氮的比例在香脂冷杉和较温暖的地点显示出更高的值。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）和更高的R _s10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，更高的凋落物输入率不会导致更高的总 SOC 储量，更温暖的气候不会导致生物反应性土壤 C 和 N 的消耗。变暖对流入和流出土壤的通量都有积极影响土壤以及稳定的 SOC 的潜在饱和度可以解释适用于本研究背景的这些结果：寒冷潮湿的环境以及沿温度梯度的稳定植被组成。虽然整个研究区域都受制于潮湿的气候，