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Effects of experimental warming of air, soil and permafrost on carbon balance in Alaskan tundra

机译：空气，土壤和多年冻土的实验变暖对阿拉斯加冻原的碳平衡的影响

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The carbon (C) storage capacity of northern latitude ecosystems may diminish as warming air temperatures increase permafrost thaw and stimulate decomposition of previously frozen soil organic C. However, warming may also enhance plant growth so that photosynthetic carbon dioxide (CO2) uptake may, in part, offset respiratory losses. To determine the effects of air and soil warming on CO2 exchange in tundra, we established an ecosystem warming experiment - the Carbon in Permafrost Experimental Heating Research (CiPEHR) project - in the northern foothills of the Alaska Range in Interior Alaska. We used snow fences coupled with spring snow removal to increase deep soil temperatures and thaw depth (winter warming) and open-top chambers to increase growing season air temperatures (summer warming). Winter warming increased soil temperature (integrated 5-40 cm depth) by 1.5 degrees C, which resulted in a 10% increase in growing season thaw depth. Surprisingly, the additional 2 kg of thawed soil C m-2 in the winter warming plots did not result in significant changes in cumulative growing season respiration, which may have been inhibited by soil saturation at the base of the active layer. In contrast to the limited effects on growing-season C dynamics, winter warming caused drastic changes in winter respiration and altered the annual C balance of this ecosystem by doubling the net loss of CO2 to the atmosphere. While most changes to the abiotic environment at CiPEHR were driven by winter warming, summer warming effects on plant and soil processes resulted in 20% increases in both gross primary productivity and growing season ecosystem respiration and significantly altered the age and sources of CO2 respired from this ecosystem. These results demonstrate the vulnerability of organic C stored in near surface permafrost to increasing temperatures and the strong potential for warming tundra to serve as a positive feedback to global climate change.
机译：北部纬度生态系统的碳（C）储存能力可能会随着气温的升高而增加永冻土的融化并刺激先前冻结的土壤有机C的分解。但是，变暖也可能会促进植物的生长，从而使光合二氧化碳（CO2）的吸收部分，抵消呼吸损失。为了确定空气和土壤变暖对苔原中CO2交换的影响，我们在阿拉斯加内陆阿拉斯加山脉北麓建立了一个生态系统变暖实验-多年冻土中的碳实验加热研究（CiPEHR）项目。我们使用了防雪栅栏和春季除雪技术，以提高土壤深层温度和融化深度（冬季变暖），并采用开放式隔室来提高生长季节的气温（夏季变暖）。冬季变暖使土壤温度（综合5-40厘米深度）增加了1.5摄氏度，这导致生长季节的融化深度增加了10％。出乎意料的是，冬季变暖区中增加的2 kg解冻土壤C m-2并未导致累积生长期呼吸的显着变化，这可能已被活性层底部的土壤饱和所抑制。与对生长季节C动态的有限影响相反，冬季变暖导致冬季呼吸急剧变化，并通过使大气中CO2净损失增加一倍，改变了该生态系统的年度C平衡。尽管CiPEHR非生物环境的大多数变化是由冬季变暖推动的，但夏季变暖对植物和土壤过程的影响导致初级生产力总值和生长期生态系统呼吸均增加了20％，并显着改变了从中呼吸的二氧化碳的年龄和来源生态系统。这些结果表明，存储在近地表多年冻土中的有机碳易受温度升高的影响，并且有可能使苔原变暖，以作为对全球气候变化的积极反馈。

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