Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775, USA.
Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, 47907, USA.
Ecol Appl. 2018 Jan;28(1):5-27. doi: 10.1002/eap.1641. Epub 2017 Dec 27.
It is important to understand how upland ecosystems of Alaska, which are estimated to occupy 84% of the state (i.e., 1,237,774 km ), are influencing and will influence state-wide carbon (C) dynamics in the face of ongoing climate change. We coupled fire disturbance and biogeochemical models to assess the relative effects of changing atmospheric carbon dioxide (CO ), climate, logging and fire regimes on the historical and future C balance of upland ecosystems for the four main Landscape Conservation Cooperatives (LCCs) of Alaska. At the end of the historical period (1950-2009) of our analysis, we estimate that upland ecosystems of Alaska store ~50 Pg C (with ~90% of the C in soils), and gained 3.26 Tg C/yr. Three of the LCCs had gains in total ecosystem C storage, while the Northwest Boreal LCC lost C (-6.01 Tg C/yr) because of increases in fire activity. Carbon exports from logging affected only the North Pacific LCC and represented less than 1% of the state's net primary production (NPP). The analysis for the future time period (2010-2099) consisted of six simulations driven by climate outputs from two climate models for three emission scenarios. Across the climate scenarios, total ecosystem C storage increased between 19.5 and 66.3 Tg C/yr, which represents 3.4% to 11.7% increase in Alaska upland's storage. We conducted additional simulations to attribute these responses to environmental changes. This analysis showed that atmospheric CO fertilization was the main driver of ecosystem C balance. By comparing future simulations with constant and with increasing atmospheric CO , we estimated that the sensitivity of NPP was 4.8% per 100 ppmv, but NPP becomes less sensitive to CO increase throughout the 21st century. Overall, our analyses suggest that the decreasing CO sensitivity of NPP and the increasing sensitivity of heterotrophic respiration to air temperature, in addition to the increase in C loss from wildfires weakens the C sink from upland ecosystems of Alaska and will ultimately lead to a source of CO to the atmosphere beyond 2100. Therefore, we conclude that the increasing regional C sink we estimate for the 21st century will most likely be transitional.
了解阿拉斯加旱地生态系统（估计占该州 84%的面积，即 1,237,774 平方公里）如何影响并将影响全州范围内的碳（C）动态，这一点很重要。在持续的气候变化面前，我们结合火灾干扰和生物地球化学模型，以评估不断变化的大气二氧化碳（CO ）、气候、采伐和火灾制度对阿拉斯加四个主要景观保护合作区（LCC）旱地生态系统的历史和未来 C 平衡的相对影响。在我们分析的历史时期（1950-2009 年）结束时，我们估计阿拉斯加旱地生态系统储存了约 50 Pg C（其中 90%的 C 在土壤中），并每年增加 3.26 Tg C。三个 LCC 的总生态系统 C 储存量有所增加，而西北北方森林 LCC 由于火灾活动增加而失去了 C（-6.01 Tg C/yr）。伐木造成的碳出口仅影响北太平洋 LCC，占该州净初级生产力（NPP）的不到 1%。未来时期（2010-2099 年）的分析由两种气候模型的气候输出驱动的六个模拟组成，这些模拟考虑了三种排放情景。在所有气候情景下，总生态系统 C 储存量增加了 19.5 到 66.3 Tg C/yr，这代表阿拉斯加旱地存储量增加了 3.4%到 11.7%。我们进行了额外的模拟，以将这些响应归因于环境变化。该分析表明，大气 CO 施肥是生态系统 C 平衡的主要驱动因素。通过将未来模拟与大气 CO 浓度保持不变和不断增加的情景进行比较，我们估计 NPP 的敏感性为每 100 ppmv 增加 4.8%，但在 21 世纪，NPP 对 CO 增加的敏感性会降低。总的来说，我们的分析表明，NPP 对 CO 的敏感性降低以及异养呼吸对空气温度的敏感性增加，加上野火造成的 C 损失增加，削弱了阿拉斯加旱地生态系统的碳汇，最终导致大气中 CO 的源在 2100 年之后增加。因此，我们的结论是，我们估计 21 世纪不断增加的区域碳汇很可能是过渡性的。
