Warming of the Arctic can stimulate microbial decomposition and release of permafrost soil carbon (C) as greenhouse gases, and thus has the potential to influence climate change. At the same time, plant growth can be stimulated and offset C release. This study presents a 15-year time series comprising chamber and eddy covariance measurements of net ecosystem C exchange in a tundra ecosystem in Alaska where permafrost has been degrading due to regional warming. The site was a carbon dioxide source to the atmosphere with a cumulative total loss of 781.6 g C m⁻² over the study period. Both gross primary productivity (GPP) and ecosystem respiration (R_eco) were already likely higher than historical levels such that increases in R_eco losses overwhelmed GPP gains in most years. This shift to a net C source to the atmosphere likely started in the early 1990s when permafrost was observed to warm and thaw at the site. Shifts in the plant community occur more slowly and are likely to constrain future GPP increases as compared to more rapid shifts in the microbial community that contribute to increased R_eco. Observed rates suggest that cumulative net soil C loss of 4.18–10.00 kg C m⁻²—8%–20% of the current active layer soil C pool—could occur from 2020 to the end of the century. This amount of permafrost C loss to the atmosphere represents a significant accelerating feedback to climate change if it were to occur at a similar magnitude across the permafrost region.

中文翻译：

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在 15 年的测量中，通过融化永久冻土层将碳持续排放到大气中

北极变暖会刺激微生物分解并释放永久冻土碳（C）作为温室气体，因此有可能影响气候变化。同时，可以刺激植物生长，抵消碳释放。本研究展示了一个 15 年的时间序列，包括对阿拉斯加苔原生态系统中净生态系统 C 交换的腔室和涡流协方差测量，那里的永久冻土层因区域变暖而退化。该场地是大气中的二氧化碳源，在研究期间累计总损失为 781.6 g C m ^-2。总初级生产力 (GPP) 和生态系统呼吸 ( R _eco ) 都可能已经高于历史水平，因此R _eco在大多数年份，损失超过了 GPP 的收益。这种向大气中净碳源的转变可能始于 1990 年代初，当时观测到该地点的永久冻土变暖和解冻。与有助于增加R _eco的微生物群落的更快速变化相比，植物群落的变化发生得更慢，并且可能会限制未来 GPP 的增加。观察到的速率表明，从 2020 年到本世纪末，可能会发生4.18–10.00 kg C m ^-2 —当前活动层土壤碳库的 8%–20% 的累积净土壤碳损失。如果在整个永久冻土地区以类似的幅度发生，那么向大气中流失的永久冻土 C 的数量代表了对气候变化的显着加速反馈。